[PATCH v5 00/20] MST refcounting/atomic helpers cleanup

[PATCH v5 00/20] MST refcounting/atomic helpers cleanup

[Lyude Paul]

This is the series I've been working on for a while now to get all of
the atomic DRM drivers in the tree to use the atomic MST helpers, and to
make the atomic MST helpers actually idempotent. Turns out it's a lot
more difficult to do that without also fixing how port and branch device
refcounting works so that it actually makes sense, since the current
upstream implementation requires a ton of magic in the atomic helpers to
work around properly and in many situations just plain doesn't work as
intended.

There's still more cleanup that can be done, but I think this is a good
place to start off for now :).

Also available on gitlab:

https://gitlab.freedesktop.org/lyudess/linux/commits/wip/mst-dual-kref-start-v5

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Juston Li <juston.li@intel.com>

Lyude Paul (20):
  drm/dp_mst: Fix some formatting in drm_dp_add_port()
  drm/dp_mst: Fix some formatting in drm_dp_payload_send_msg()
  drm/dp_mst: Fix some formatting in drm_dp_mst_allocate_vcpi()
  drm/dp_mst: Fix some formatting in drm_dp_mst_deallocate_vcpi()
  drm/dp_mst: Rename drm_dp_mst_get_validated_(port|mstb)_ref and
    friends
  drm/dp_mst: Introduce new refcounting scheme for mstbs and ports
  drm/dp_mst: Restart last_connected_port_and_mstb() if topology ref
    fails
  drm/dp_mst: Stop releasing VCPI when removing ports from topology
  drm/dp_mst: Fix payload deallocation on hotplugs using malloc refs
  drm/i915: Keep malloc references to MST ports
  drm/amdgpu/display: Keep malloc ref to MST port
  drm/nouveau: Remove bogus cleanup in nv50_mstm_add_connector()
  drm/nouveau: Remove unnecessary VCPI checks in nv50_msto_cleanup()
  drm/nouveau: Keep malloc references to MST ports
  drm/nouveau: Stop unsetting mstc->port, use malloc refs
  drm/nouveau: Grab payload lock in nv50_msto_payload()
  drm/dp_mst: Add some atomic state iterator macros
  drm/dp_mst: Start tracking per-port VCPI allocations
  drm/dp_mst: Check payload count in drm_dp_mst_atomic_check()
  drm/nouveau: Use atomic VCPI helpers for MST

 .../gpu/dp-mst/topology-figure-1.dot          |  52 +
 .../gpu/dp-mst/topology-figure-2.dot          |  56 +
 .../gpu/dp-mst/topology-figure-3.dot          |  59 ++
 Documentation/gpu/drm-kms-helpers.rst         |  26 +-
 .../display/amdgpu_dm/amdgpu_dm_mst_types.c   |  11 +-
 drivers/gpu/drm/drm_dp_mst_topology.c         | 955 ++++++++++++++----
 drivers/gpu/drm/i915/intel_connector.c        |   4 +
 drivers/gpu/drm/i915/intel_display.c          |   4 +
 drivers/gpu/drm/i915/intel_dp_mst.c           |  55 +-
 drivers/gpu/drm/nouveau/dispnv50/disp.c       |  96 +-
 include/drm/drm_dp_mst_helper.h               | 151 ++-
 11 files changed, 1213 insertions(+), 256 deletions(-)
 create mode 100644 Documentation/gpu/dp-mst/topology-figure-1.dot
 create mode 100644 Documentation/gpu/dp-mst/topology-figure-2.dot
 create mode 100644 Documentation/gpu/dp-mst/topology-figure-3.dot

-- 
2.20.1

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[PATCH v5 01/20] drm/dp_mst: Fix some formatting in drm_dp_add_port()

[Lyude Paul]

Reindent some stuff, and split some stuff across multiple lines so we
aren't going over the text width limit.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 2ab16c9e6243..c93bff5527fd 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1184,11 +1184,13 @@ static void drm_dp_add_port(struct drm_dp_mst_branch *mstb,
 
 	if (old_ddps != port->ddps) {
 		if (port->ddps) {
-			if (!port->input)
-				drm_dp_send_enum_path_resources(mstb->mgr, mstb, port);
+			if (!port->input) {
+				drm_dp_send_enum_path_resources(mstb->mgr,
+								mstb, port);
+			}
 		} else {
 			port->available_pbn = 0;
-			}
+		}
 	}
 
 	if (old_pdt != port->pdt && !port->input) {
@@ -1202,8 +1204,11 @@ static void drm_dp_add_port(struct drm_dp_mst_branch *mstb,
 	if (created && !port->input) {
 		char proppath[255];
 
-		build_mst_prop_path(mstb, port->port_num, proppath, sizeof(proppath));
-		port->connector = (*mstb->mgr->cbs->add_connector)(mstb->mgr, port, proppath);
+		build_mst_prop_path(mstb, port->port_num, proppath,
+				    sizeof(proppath));
+		port->connector = (*mstb->mgr->cbs->add_connector)(mstb->mgr,
+								   port,
+								   proppath);
 		if (!port->connector) {
 			/* remove it from the port list */
 			mutex_lock(&mstb->mgr->lock);
@@ -1216,7 +1221,8 @@ static void drm_dp_add_port(struct drm_dp_mst_branch *mstb,
 		if ((port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV ||
 		     port->pdt == DP_PEER_DEVICE_SST_SINK) &&
 		    port->port_num >= DP_MST_LOGICAL_PORT_0) {
-			port->cached_edid = drm_get_edid(port->connector, &port->aux.ddc);
+			port->cached_edid = drm_get_edid(port->connector,
+							 &port->aux.ddc);
 			drm_connector_set_tile_property(port->connector);
 		}
 		(*mstb->mgr->cbs->register_connector)(port->connector);
-- 
2.20.1

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[PATCH v5 02/20] drm/dp_mst: Fix some formatting in drm_dp_payload_send_msg()

[Lyude Paul]

Split some stuff across multiple lines, remove some unnecessary braces

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index c93bff5527fd..fc93a71c42b0 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1331,9 +1331,9 @@ static struct drm_dp_mst_branch *get_mst_branch_device_by_guid_helper(
 	return NULL;
 }
 
-static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device_by_guid(
-	struct drm_dp_mst_topology_mgr *mgr,
-	uint8_t *guid)
+static struct drm_dp_mst_branch *
+drm_dp_get_mst_branch_device_by_guid(struct drm_dp_mst_topology_mgr *mgr,
+				     uint8_t *guid)
 {
 	struct drm_dp_mst_branch *mstb;
 
@@ -1739,7 +1739,9 @@ static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
 	port_num = port->port_num;
 	mstb = drm_dp_get_validated_mstb_ref(mgr, port->parent);
 	if (!mstb) {
-		mstb = drm_dp_get_last_connected_port_and_mstb(mgr, port->parent, &port_num);
+		mstb = drm_dp_get_last_connected_port_and_mstb(mgr,
+							       port->parent,
+							       &port_num);
 
 		if (!mstb) {
 			drm_dp_put_port(port);
@@ -1765,9 +1767,9 @@ static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
 
 	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
 	if (ret > 0) {
-		if (txmsg->reply.reply_type == 1) {
+		if (txmsg->reply.reply_type == 1)
 			ret = -EINVAL;
-		} else
+		else
 			ret = 0;
 	}
 	kfree(txmsg);
-- 
2.20.1

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[PATCH v5 03/20] drm/dp_mst: Fix some formatting in drm_dp_mst_allocate_vcpi()

[Lyude Paul]

Fix some indenting, split some stuff across multiple lines.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index fc93a71c42b0..a63a4d32962a 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2731,7 +2731,8 @@ bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 		return false;
 
 	if (port->vcpi.vcpi > 0) {
-		DRM_DEBUG_KMS("payload: vcpi %d already allocated for pbn %d - requested pbn %d\n", port->vcpi.vcpi, port->vcpi.pbn, pbn);
+		DRM_DEBUG_KMS("payload: vcpi %d already allocated for pbn %d - requested pbn %d\n",
+			      port->vcpi.vcpi, port->vcpi.pbn, pbn);
 		if (pbn == port->vcpi.pbn) {
 			drm_dp_put_port(port);
 			return true;
@@ -2741,11 +2742,11 @@ bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 	ret = drm_dp_init_vcpi(mgr, &port->vcpi, pbn, slots);
 	if (ret) {
 		DRM_DEBUG_KMS("failed to init vcpi slots=%d max=63 ret=%d\n",
-				DIV_ROUND_UP(pbn, mgr->pbn_div), ret);
+			      DIV_ROUND_UP(pbn, mgr->pbn_div), ret);
 		goto out;
 	}
 	DRM_DEBUG_KMS("initing vcpi for pbn=%d slots=%d\n",
-			pbn, port->vcpi.num_slots);
+		      pbn, port->vcpi.num_slots);
 
 	drm_dp_put_port(port);
 	return true;
-- 
2.20.1

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[PATCH v5 04/20] drm/dp_mst: Fix some formatting in drm_dp_mst_deallocate_vcpi()

[Lyude Paul]

Split some stuff across multiple lines

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index a63a4d32962a..75cca6a843fb 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2790,7 +2790,8 @@ EXPORT_SYMBOL(drm_dp_mst_reset_vcpi_slots);
  * @mgr: manager for this port
  * @port: unverified port to deallocate vcpi for
  */
-void drm_dp_mst_deallocate_vcpi(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port)
+void drm_dp_mst_deallocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
+				struct drm_dp_mst_port *port)
 {
 	port = drm_dp_get_validated_port_ref(mgr, port);
 	if (!port)
-- 
2.20.1

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[PATCH v5 05/20] drm/dp_mst: Rename drm_dp_mst_get_validated_(port|mstb)_ref and friends

[Lyude Paul]

s/drm_dp_get_validated_port_ref/drm_dp_mst_topology_get_port_validated/
s/drm_dp_put_port/drm_dp_mst_topology_put_port/
s/drm_dp_get_validated_mstb_ref/drm_dp_mst_topology_get_mstb_validated/
s/drm_dp_put_mst_branch_device/drm_dp_mst_topology_put_mstb/

This is a much more consistent naming scheme, and will make even more
sense once we redesign how the current refcounting scheme here works.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 114 ++++++++++++++------------
 1 file changed, 62 insertions(+), 52 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 75cca6a843fb..074e985093ca 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -46,7 +46,7 @@ static bool dump_dp_payload_table(struct drm_dp_mst_topology_mgr *mgr,
 				  char *buf);
 static int test_calc_pbn_mode(void);
 
-static void drm_dp_put_port(struct drm_dp_mst_port *port);
+static void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port);
 
 static int drm_dp_dpcd_write_payload(struct drm_dp_mst_topology_mgr *mgr,
 				     int id,
@@ -888,7 +888,7 @@ static void drm_dp_destroy_mst_branch_device(struct kref *kref)
 	 */
 	list_for_each_entry_safe(port, tmp, &mstb->ports, next) {
 		list_del(&port->next);
-		drm_dp_put_port(port);
+		drm_dp_mst_topology_put_port(port);
 	}
 
 	/* drop any tx slots msg */
@@ -911,7 +911,7 @@ static void drm_dp_destroy_mst_branch_device(struct kref *kref)
 	kref_put(kref, drm_dp_free_mst_branch_device);
 }
 
-static void drm_dp_put_mst_branch_device(struct drm_dp_mst_branch *mstb)
+static void drm_dp_mst_topology_put_mstb(struct drm_dp_mst_branch *mstb)
 {
 	kref_put(&mstb->kref, drm_dp_destroy_mst_branch_device);
 }
@@ -930,7 +930,7 @@ static void drm_dp_port_teardown_pdt(struct drm_dp_mst_port *port, int old_pdt)
 	case DP_PEER_DEVICE_MST_BRANCHING:
 		mstb = port->mstb;
 		port->mstb = NULL;
-		drm_dp_put_mst_branch_device(mstb);
+		drm_dp_mst_topology_put_mstb(mstb);
 		break;
 	}
 }
@@ -970,12 +970,14 @@ static void drm_dp_destroy_port(struct kref *kref)
 	kfree(port);
 }
 
-static void drm_dp_put_port(struct drm_dp_mst_port *port)
+static void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port)
 {
 	kref_put(&port->kref, drm_dp_destroy_port);
 }
 
-static struct drm_dp_mst_branch *drm_dp_mst_get_validated_mstb_ref_locked(struct drm_dp_mst_branch *mstb, struct drm_dp_mst_branch *to_find)
+static struct drm_dp_mst_branch *
+drm_dp_mst_topology_get_mstb_validated_locked(struct drm_dp_mst_branch *mstb,
+					      struct drm_dp_mst_branch *to_find)
 {
 	struct drm_dp_mst_port *port;
 	struct drm_dp_mst_branch *rmstb;
@@ -985,7 +987,8 @@ static struct drm_dp_mst_branch *drm_dp_mst_get_validated_mstb_ref_locked(struct
 	}
 	list_for_each_entry(port, &mstb->ports, next) {
 		if (port->mstb) {
-			rmstb = drm_dp_mst_get_validated_mstb_ref_locked(port->mstb, to_find);
+			rmstb = drm_dp_mst_topology_get_mstb_validated_locked(
+			    port->mstb, to_find);
 			if (rmstb)
 				return rmstb;
 		}
@@ -993,12 +996,15 @@ static struct drm_dp_mst_branch *drm_dp_mst_get_validated_mstb_ref_locked(struct
 	return NULL;
 }
 
-static struct drm_dp_mst_branch *drm_dp_get_validated_mstb_ref(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_branch *mstb)
+static struct drm_dp_mst_branch *
+drm_dp_mst_topology_get_mstb_validated(struct drm_dp_mst_topology_mgr *mgr,
+				       struct drm_dp_mst_branch *mstb)
 {
 	struct drm_dp_mst_branch *rmstb = NULL;
 	mutex_lock(&mgr->lock);
 	if (mgr->mst_primary)
-		rmstb = drm_dp_mst_get_validated_mstb_ref_locked(mgr->mst_primary, mstb);
+		rmstb = drm_dp_mst_topology_get_mstb_validated_locked(
+		    mgr->mst_primary, mstb);
 	mutex_unlock(&mgr->lock);
 	return rmstb;
 }
@@ -1021,7 +1027,9 @@ static struct drm_dp_mst_port *drm_dp_mst_get_port_ref_locked(struct drm_dp_mst_
 	return NULL;
 }
 
-static struct drm_dp_mst_port *drm_dp_get_validated_port_ref(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port)
+static struct drm_dp_mst_port *
+drm_dp_mst_topology_get_port_validated(struct drm_dp_mst_topology_mgr *mgr,
+				       struct drm_dp_mst_port *port)
 {
 	struct drm_dp_mst_port *rport = NULL;
 	mutex_lock(&mgr->lock);
@@ -1215,7 +1223,7 @@ static void drm_dp_add_port(struct drm_dp_mst_branch *mstb,
 			list_del(&port->next);
 			mutex_unlock(&mstb->mgr->lock);
 			/* drop port list reference */
-			drm_dp_put_port(port);
+			drm_dp_mst_topology_put_port(port);
 			goto out;
 		}
 		if ((port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV ||
@@ -1230,7 +1238,7 @@ static void drm_dp_add_port(struct drm_dp_mst_branch *mstb,
 
 out:
 	/* put reference to this port */
-	drm_dp_put_port(port);
+	drm_dp_mst_topology_put_port(port);
 }
 
 static void drm_dp_update_port(struct drm_dp_mst_branch *mstb,
@@ -1265,7 +1273,7 @@ static void drm_dp_update_port(struct drm_dp_mst_branch *mstb,
 			dowork = true;
 	}
 
-	drm_dp_put_port(port);
+	drm_dp_mst_topology_put_port(port);
 	if (dowork)
 		queue_work(system_long_wq, &mstb->mgr->work);
 
@@ -1368,10 +1376,11 @@ static void drm_dp_check_and_send_link_address(struct drm_dp_mst_topology_mgr *m
 			drm_dp_send_enum_path_resources(mgr, mstb, port);
 
 		if (port->mstb) {
-			mstb_child = drm_dp_get_validated_mstb_ref(mgr, port->mstb);
+			mstb_child = drm_dp_mst_topology_get_mstb_validated(
+			    mgr, port->mstb);
 			if (mstb_child) {
 				drm_dp_check_and_send_link_address(mgr, mstb_child);
-				drm_dp_put_mst_branch_device(mstb_child);
+				drm_dp_mst_topology_put_mstb(mstb_child);
 			}
 		}
 	}
@@ -1390,7 +1399,7 @@ static void drm_dp_mst_link_probe_work(struct work_struct *work)
 	mutex_unlock(&mgr->lock);
 	if (mstb) {
 		drm_dp_check_and_send_link_address(mgr, mstb);
-		drm_dp_put_mst_branch_device(mstb);
+		drm_dp_mst_topology_put_mstb(mstb);
 	}
 }
 
@@ -1732,19 +1741,19 @@ static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
 	u8 sinks[DRM_DP_MAX_SDP_STREAMS];
 	int i;
 
-	port = drm_dp_get_validated_port_ref(mgr, port);
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
 	if (!port)
 		return -EINVAL;
 
 	port_num = port->port_num;
-	mstb = drm_dp_get_validated_mstb_ref(mgr, port->parent);
+	mstb = drm_dp_mst_topology_get_mstb_validated(mgr, port->parent);
 	if (!mstb) {
 		mstb = drm_dp_get_last_connected_port_and_mstb(mgr,
 							       port->parent,
 							       &port_num);
 
 		if (!mstb) {
-			drm_dp_put_port(port);
+			drm_dp_mst_topology_put_port(port);
 			return -EINVAL;
 		}
 	}
@@ -1774,8 +1783,8 @@ static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
 	}
 	kfree(txmsg);
 fail_put:
-	drm_dp_put_mst_branch_device(mstb);
-	drm_dp_put_port(port);
+	drm_dp_mst_topology_put_mstb(mstb);
+	drm_dp_mst_topology_put_port(port);
 	return ret;
 }
 
@@ -1785,13 +1794,13 @@ int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
 	struct drm_dp_sideband_msg_tx *txmsg;
 	int len, ret;
 
-	port = drm_dp_get_validated_port_ref(mgr, port);
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
 	if (!port)
 		return -EINVAL;
 
 	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
 	if (!txmsg) {
-		drm_dp_put_port(port);
+		drm_dp_mst_topology_put_port(port);
 		return -ENOMEM;
 	}
 
@@ -1807,7 +1816,7 @@ int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
 			ret = 0;
 	}
 	kfree(txmsg);
-	drm_dp_put_port(port);
+	drm_dp_mst_topology_put_port(port);
 
 	return ret;
 }
@@ -1896,7 +1905,8 @@ int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr)
 		if (vcpi) {
 			port = container_of(vcpi, struct drm_dp_mst_port,
 					    vcpi);
-			port = drm_dp_get_validated_port_ref(mgr, port);
+			port = drm_dp_mst_topology_get_port_validated(mgr,
+								      port);
 			if (!port) {
 				mutex_unlock(&mgr->payload_lock);
 				return -EINVAL;
@@ -1933,7 +1943,7 @@ int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr)
 		cur_slots += req_payload.num_slots;
 
 		if (port)
-			drm_dp_put_port(port);
+			drm_dp_mst_topology_put_port(port);
 	}
 
 	for (i = 0; i < mgr->max_payloads; i++) {
@@ -2032,7 +2042,7 @@ static int drm_dp_send_dpcd_write(struct drm_dp_mst_topology_mgr *mgr,
 	struct drm_dp_sideband_msg_tx *txmsg;
 	struct drm_dp_mst_branch *mstb;
 
-	mstb = drm_dp_get_validated_mstb_ref(mgr, port->parent);
+	mstb = drm_dp_mst_topology_get_mstb_validated(mgr, port->parent);
 	if (!mstb)
 		return -EINVAL;
 
@@ -2056,7 +2066,7 @@ static int drm_dp_send_dpcd_write(struct drm_dp_mst_topology_mgr *mgr,
 	}
 	kfree(txmsg);
 fail_put:
-	drm_dp_put_mst_branch_device(mstb);
+	drm_dp_mst_topology_put_mstb(mstb);
 	return ret;
 }
 
@@ -2200,7 +2210,7 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
 out_unlock:
 	mutex_unlock(&mgr->lock);
 	if (mstb)
-		drm_dp_put_mst_branch_device(mstb);
+		drm_dp_mst_topology_put_mstb(mstb);
 	return ret;
 
 }
@@ -2365,7 +2375,7 @@ static int drm_dp_mst_handle_down_rep(struct drm_dp_mst_topology_mgr *mgr)
 			       mgr->down_rep_recv.initial_hdr.lct,
 				      mgr->down_rep_recv.initial_hdr.rad[0],
 				      mgr->down_rep_recv.msg[0]);
-			drm_dp_put_mst_branch_device(mstb);
+			drm_dp_mst_topology_put_mstb(mstb);
 			memset(&mgr->down_rep_recv, 0, sizeof(struct drm_dp_sideband_msg_rx));
 			return 0;
 		}
@@ -2376,7 +2386,7 @@ static int drm_dp_mst_handle_down_rep(struct drm_dp_mst_topology_mgr *mgr)
 		}
 
 		memset(&mgr->down_rep_recv, 0, sizeof(struct drm_dp_sideband_msg_rx));
-		drm_dp_put_mst_branch_device(mstb);
+		drm_dp_mst_topology_put_mstb(mstb);
 
 		mutex_lock(&mgr->qlock);
 		txmsg->state = DRM_DP_SIDEBAND_TX_RX;
@@ -2449,7 +2459,7 @@ static int drm_dp_mst_handle_up_req(struct drm_dp_mst_topology_mgr *mgr)
 		}
 
 		if (mstb)
-			drm_dp_put_mst_branch_device(mstb);
+			drm_dp_mst_topology_put_mstb(mstb);
 
 		memset(&mgr->up_req_recv, 0, sizeof(struct drm_dp_sideband_msg_rx));
 	}
@@ -2509,7 +2519,7 @@ enum drm_connector_status drm_dp_mst_detect_port(struct drm_connector *connector
 	enum drm_connector_status status = connector_status_disconnected;
 
 	/* we need to search for the port in the mgr in case its gone */
-	port = drm_dp_get_validated_port_ref(mgr, port);
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
 	if (!port)
 		return connector_status_disconnected;
 
@@ -2534,7 +2544,7 @@ enum drm_connector_status drm_dp_mst_detect_port(struct drm_connector *connector
 		break;
 	}
 out:
-	drm_dp_put_port(port);
+	drm_dp_mst_topology_put_port(port);
 	return status;
 }
 EXPORT_SYMBOL(drm_dp_mst_detect_port);
@@ -2551,11 +2561,11 @@ bool drm_dp_mst_port_has_audio(struct drm_dp_mst_topology_mgr *mgr,
 {
 	bool ret = false;
 
-	port = drm_dp_get_validated_port_ref(mgr, port);
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
 	if (!port)
 		return ret;
 	ret = port->has_audio;
-	drm_dp_put_port(port);
+	drm_dp_mst_topology_put_port(port);
 	return ret;
 }
 EXPORT_SYMBOL(drm_dp_mst_port_has_audio);
@@ -2575,7 +2585,7 @@ struct edid *drm_dp_mst_get_edid(struct drm_connector *connector, struct drm_dp_
 	struct edid *edid = NULL;
 
 	/* we need to search for the port in the mgr in case its gone */
-	port = drm_dp_get_validated_port_ref(mgr, port);
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
 	if (!port)
 		return NULL;
 
@@ -2586,7 +2596,7 @@ struct edid *drm_dp_mst_get_edid(struct drm_connector *connector, struct drm_dp_
 		drm_connector_set_tile_property(connector);
 	}
 	port->has_audio = drm_detect_monitor_audio(edid);
-	drm_dp_put_port(port);
+	drm_dp_mst_topology_put_port(port);
 	return edid;
 }
 EXPORT_SYMBOL(drm_dp_mst_get_edid);
@@ -2657,7 +2667,7 @@ int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
 	if (IS_ERR(topology_state))
 		return PTR_ERR(topology_state);
 
-	port = drm_dp_get_validated_port_ref(mgr, port);
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
 	if (port == NULL)
 		return -EINVAL;
 	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
@@ -2665,14 +2675,14 @@ int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
 			req_slots, topology_state->avail_slots);
 
 	if (req_slots > topology_state->avail_slots) {
-		drm_dp_put_port(port);
+		drm_dp_mst_topology_put_port(port);
 		return -ENOSPC;
 	}
 
 	topology_state->avail_slots -= req_slots;
 	DRM_DEBUG_KMS("vcpi slots avail=%d", topology_state->avail_slots);
 
-	drm_dp_put_port(port);
+	drm_dp_mst_topology_put_port(port);
 	return req_slots;
 }
 EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
@@ -2723,7 +2733,7 @@ bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 {
 	int ret;
 
-	port = drm_dp_get_validated_port_ref(mgr, port);
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
 	if (!port)
 		return false;
 
@@ -2734,7 +2744,7 @@ bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 		DRM_DEBUG_KMS("payload: vcpi %d already allocated for pbn %d - requested pbn %d\n",
 			      port->vcpi.vcpi, port->vcpi.pbn, pbn);
 		if (pbn == port->vcpi.pbn) {
-			drm_dp_put_port(port);
+			drm_dp_mst_topology_put_port(port);
 			return true;
 		}
 	}
@@ -2748,7 +2758,7 @@ bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 	DRM_DEBUG_KMS("initing vcpi for pbn=%d slots=%d\n",
 		      pbn, port->vcpi.num_slots);
 
-	drm_dp_put_port(port);
+	drm_dp_mst_topology_put_port(port);
 	return true;
 out:
 	return false;
@@ -2758,12 +2768,12 @@ EXPORT_SYMBOL(drm_dp_mst_allocate_vcpi);
 int drm_dp_mst_get_vcpi_slots(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port)
 {
 	int slots = 0;
-	port = drm_dp_get_validated_port_ref(mgr, port);
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
 	if (!port)
 		return slots;
 
 	slots = port->vcpi.num_slots;
-	drm_dp_put_port(port);
+	drm_dp_mst_topology_put_port(port);
 	return slots;
 }
 EXPORT_SYMBOL(drm_dp_mst_get_vcpi_slots);
@@ -2777,11 +2787,11 @@ EXPORT_SYMBOL(drm_dp_mst_get_vcpi_slots);
  */
 void drm_dp_mst_reset_vcpi_slots(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port)
 {
-	port = drm_dp_get_validated_port_ref(mgr, port);
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
 	if (!port)
 		return;
 	port->vcpi.num_slots = 0;
-	drm_dp_put_port(port);
+	drm_dp_mst_topology_put_port(port);
 }
 EXPORT_SYMBOL(drm_dp_mst_reset_vcpi_slots);
 
@@ -2793,7 +2803,7 @@ EXPORT_SYMBOL(drm_dp_mst_reset_vcpi_slots);
 void drm_dp_mst_deallocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 				struct drm_dp_mst_port *port)
 {
-	port = drm_dp_get_validated_port_ref(mgr, port);
+	port = drm_dp_mst_topology_get_port_validated(mgr, port);
 	if (!port)
 		return;
 
@@ -2802,7 +2812,7 @@ void drm_dp_mst_deallocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 	port->vcpi.pbn = 0;
 	port->vcpi.aligned_pbn = 0;
 	port->vcpi.vcpi = 0;
-	drm_dp_put_port(port);
+	drm_dp_mst_topology_put_port(port);
 }
 EXPORT_SYMBOL(drm_dp_mst_deallocate_vcpi);
 
@@ -3302,7 +3312,7 @@ static int drm_dp_mst_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs
 	struct drm_dp_sideband_msg_tx *txmsg = NULL;
 	int ret;
 
-	mstb = drm_dp_get_validated_mstb_ref(mgr, port->parent);
+	mstb = drm_dp_mst_topology_get_mstb_validated(mgr, port->parent);
 	if (!mstb)
 		return -EREMOTEIO;
 
@@ -3352,7 +3362,7 @@ static int drm_dp_mst_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs
 	}
 out:
 	kfree(txmsg);
-	drm_dp_put_mst_branch_device(mstb);
+	drm_dp_mst_topology_put_mstb(mstb);
 	return ret;
 }
 
-- 
2.20.1

_______________________________________________
Nouveau mailing list
Nouveau@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/nouveau

[PATCH v5 06/20] drm/dp_mst: Introduce new refcounting scheme for mstbs and ports

[Lyude Paul]

The current way of handling refcounting in the DP MST helpers is really
confusing and probably just plain wrong because it's been hacked up many
times over the years without anyone actually going over the code and
seeing if things could be simplified.

To the best of my understanding, the current scheme works like this:
drm_dp_mst_port and drm_dp_mst_branch both have a single refcount. When
this refcount hits 0 for either of the two, they're removed from the
topology state, but not immediately freed. Both ports and branch devices
will reinitialize their kref once it's hit 0 before actually destroying
themselves. The intended purpose behind this is so that we can avoid
problems like not being able to free a remote payload that might still
be active, due to us having removed all of the port/branch device
structures in memory, as per:

commit 91a25e463130 ("drm/dp/mst: deallocate payload on port destruction")

Which may have worked, but then it caused use-after-free errors. Being
new to MST at the time, I tried fixing it;

commit 263efde31f97 ("drm/dp/mst: Get validated port ref in drm_dp_update_payload_part1()")

But, that was broken: both drm_dp_mst_port and drm_dp_mst_branch structs
are validated in almost every DP MST helper function. Simply put, this
means we go through the topology and try to see if the given
drm_dp_mst_branch or drm_dp_mst_port is still attached to something
before trying to use it in order to avoid dereferencing freed memory
(something that has happened a LOT in the past with this library).
Because of this it doesn't actually matter whether or not we keep keep
the ports and branches around in memory as that's not enough, because
any function that validates the branches and ports passed to it will
still reject them anyway since they're no longer in the topology
structure. So, use-after-free errors were fixed but payload deallocation
was completely broken.

Two years later, AMD informed me about this issue and I attempted to
come up with a temporary fix, pending a long-overdue cleanup of this
library:

commit c54c7374ff44 ("drm/dp_mst: Skip validating ports during destruction, just ref")

But then that introduced use-after-free errors, so I quickly reverted
it:

commit 9765635b3075 ("Revert "drm/dp_mst: Skip validating ports during destruction, just ref"")

And in the process, learned that there is just no simple fix for this:
the design is just broken. Unfortunately, the usage of these helpers are
quite broken as well. Some drivers like i915 have been smart enough to
avoid accessing any kind of information from MST port structures, but
others like nouveau have assumed, understandably so, that
drm_dp_mst_port structures are normal and can just be accessed at any
time without worrying about use-after-free errors.

After a lot of discussion, me and Daniel Vetter came up with a better
idea to replace all of this.

To summarize, since this is documented far more indepth in the
documentation this patch introduces, we make it so that drm_dp_mst_port
and drm_dp_mst_branch structures have two different classes of
refcounts: topology_kref, and malloc_kref. topology_kref corresponds to
the lifetime of the given drm_dp_mst_port or drm_dp_mst_branch in it's
given topology. Once it hits zero, any associated connectors are removed
and the branch or port can no longer be validated. malloc_kref
corresponds to the lifetime of the memory allocation for the actual
structure, and will always be non-zero so long as the topology_kref is
non-zero. This gives us a way to allow callers to hold onto port and
branch device structures past their topology lifetime, and dramatically
simplifies the lifetimes of both structures. This also finally fixes the
port deallocation problem, properly.

Additionally: since this now means that we can keep ports and branch
devices allocated in memory for however long we need, we no longer need
a significant amount of the port validation that we currently do.

Additionally, there is one last scenario that this fixes, which couldn't
have been fixed properly beforehand:

- CPU1 unrefs port from topology (refcount 1->0)
- CPU2 refs port in topology(refcount 0->1)

Since we now can guarantee memory safety for ports and branches
as-needed, we also can make our main reference counting functions fix
this problem by using kref_get_unless_zero() internally so that topology
refcounts can only ever reach 0 once.

Changes since v3:
* Remove rebase detritus - danvet
* Split out purely style changes into separate patches - hwentlan

Changes since v2:
* Fix commit message - checkpatch
* s/)-1/) - 1/g - checkpatch

Changes since v1:
* Remove forward declarations - danvet
* Move "Branch device and port refcounting" section from documentation
  into kernel-doc comments - danvet
* Export internal topology lifetime functions into their own section in
  the kernel-docs - danvet
* s/@/&/g for struct references in kernel-docs - danvet
* Drop the "when they are no longer being used" bits from the kernel
  docs - danvet
* Modify diagrams to show how the DRM driver interacts with the topology
  and payloads - danvet
* Make suggested documentation changes for
  drm_dp_mst_topology_get_mstb() and drm_dp_mst_topology_get_port() -
  danvet
* Better explain the relationship between malloc refs and topology krefs
  in the documentation for drm_dp_mst_topology_get_port() and
  drm_dp_mst_topology_get_mstb() - danvet
* Fix "See also" in drm_dp_mst_topology_get_mstb() - danvet
* Rename drm_dp_mst_topology_get_(port|mstb)() ->
  drm_dp_mst_topology_try_get_(port|mstb)() and
  drm_dp_mst_topology_ref_(port|mstb)() ->
  drm_dp_mst_topology_get_(port|mstb)() - danvet
* s/should/must in docs - danvet
* WARN_ON(refcount == 0) in topology_get_(mstb|port) - danvet
* Move kdocs for mstb/port structs inline - danvet
* Split drm_dp_get_last_connected_port_and_mstb() changes into their own
  commit - danvet

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 .../gpu/dp-mst/topology-figure-1.dot          |  52 ++
 .../gpu/dp-mst/topology-figure-2.dot          |  56 +++
 .../gpu/dp-mst/topology-figure-3.dot          |  59 +++
 Documentation/gpu/drm-kms-helpers.rst         |  26 +-
 drivers/gpu/drm/drm_dp_mst_topology.c         | 457 +++++++++++++++---
 include/drm/drm_dp_mst_helper.h               |  32 +-
 6 files changed, 613 insertions(+), 69 deletions(-)
 create mode 100644 Documentation/gpu/dp-mst/topology-figure-1.dot
 create mode 100644 Documentation/gpu/dp-mst/topology-figure-2.dot
 create mode 100644 Documentation/gpu/dp-mst/topology-figure-3.dot

diff --git a/Documentation/gpu/dp-mst/topology-figure-1.dot b/Documentation/gpu/dp-mst/topology-figure-1.dot
new file mode 100644
index 000000000000..157e17c7e0b0
--- /dev/null
+++ b/Documentation/gpu/dp-mst/topology-figure-1.dot
@@ -0,0 +1,52 @@
+digraph T {
+    /* Make sure our payloads are always drawn below the driver node */
+    subgraph cluster_driver {
+        fillcolor = grey;
+        style = filled;
+        driver -> {payload1, payload2} [dir=none];
+    }
+
+    /* Driver malloc references */
+    edge [style=dashed];
+    driver -> port1;
+    driver -> port2;
+    driver -> port3:e;
+    driver -> port4;
+
+    payload1:s -> port1:e;
+    payload2:s -> port3:e;
+    edge [style=""];
+
+    subgraph cluster_topology {
+        label="Topology Manager";
+        labelloc=bottom;
+
+        /* Topology references */
+        mstb1 -> {port1, port2};
+        port1 -> mstb2;
+        port2 -> mstb3 -> {port3, port4};
+        port3 -> mstb4;
+
+        /* Malloc references */
+        edge [style=dashed;dir=back];
+        mstb1 -> {port1, port2};
+        port1 -> mstb2;
+        port2 -> mstb3 -> {port3, port4};
+        port3 -> mstb4;
+    }
+
+    driver [label="DRM driver";style=filled;shape=box;fillcolor=lightblue];
+
+    payload1 [label="Payload #1";style=filled;shape=box;fillcolor=lightblue];
+    payload2 [label="Payload #2";style=filled;shape=box;fillcolor=lightblue];
+
+    mstb1 [label="MSTB #1";style=filled;fillcolor=palegreen;shape=oval];
+    mstb2 [label="MSTB #2";style=filled;fillcolor=palegreen;shape=oval];
+    mstb3 [label="MSTB #3";style=filled;fillcolor=palegreen;shape=oval];
+    mstb4 [label="MSTB #4";style=filled;fillcolor=palegreen;shape=oval];
+
+    port1 [label="Port #1";shape=oval];
+    port2 [label="Port #2";shape=oval];
+    port3 [label="Port #3";shape=oval];
+    port4 [label="Port #4";shape=oval];
+}
diff --git a/Documentation/gpu/dp-mst/topology-figure-2.dot b/Documentation/gpu/dp-mst/topology-figure-2.dot
new file mode 100644
index 000000000000..4243dd1737cb
--- /dev/null
+++ b/Documentation/gpu/dp-mst/topology-figure-2.dot
@@ -0,0 +1,56 @@
+digraph T {
+    /* Make sure our payloads are always drawn below the driver node */
+    subgraph cluster_driver {
+        fillcolor = grey;
+        style = filled;
+        driver -> {payload1, payload2} [dir=none];
+    }
+
+    /* Driver malloc references */
+    edge [style=dashed];
+    driver -> port1;
+    driver -> port2;
+    driver -> port3:e;
+    driver -> port4 [color=red];
+
+    payload1:s -> port1:e;
+    payload2:s -> port3:e;
+    edge [style=""];
+
+    subgraph cluster_topology {
+        label="Topology Manager";
+        labelloc=bottom;
+
+        /* Topology references */
+        mstb1 -> {port1, port2};
+        port1 -> mstb2;
+        edge [color=red];
+        port2 -> mstb3 -> {port3, port4};
+        port3 -> mstb4;
+        edge [color=""];
+
+        /* Malloc references */
+        edge [style=dashed;dir=back];
+        mstb1 -> {port1, port2};
+        port1 -> mstb2;
+        port2 -> mstb3 -> port3;
+        edge [color=red];
+        mstb3 -> port4;
+        port3 -> mstb4;
+    }
+
+    mstb1 [label="MSTB #1";style=filled;fillcolor=palegreen];
+    mstb2 [label="MSTB #2";style=filled;fillcolor=palegreen];
+    mstb3 [label="MSTB #3";style=filled;fillcolor=palegreen];
+    mstb4 [label="MSTB #4";style=filled;fillcolor=grey];
+
+    port1 [label="Port #1"];
+    port2 [label="Port #2"];
+    port3 [label="Port #3"];
+    port4 [label="Port #4";style=filled;fillcolor=grey];
+
+    driver [label="DRM driver";style=filled;shape=box;fillcolor=lightblue];
+
+    payload1 [label="Payload #1";style=filled;shape=box;fillcolor=lightblue];
+    payload2 [label="Payload #2";style=filled;shape=box;fillcolor=lightblue];
+}
diff --git a/Documentation/gpu/dp-mst/topology-figure-3.dot b/Documentation/gpu/dp-mst/topology-figure-3.dot
new file mode 100644
index 000000000000..6cd78d06778b
--- /dev/null
+++ b/Documentation/gpu/dp-mst/topology-figure-3.dot
@@ -0,0 +1,59 @@
+digraph T {
+    /* Make sure our payloads are always drawn below the driver node */
+    subgraph cluster_driver {
+        fillcolor = grey;
+        style = filled;
+        edge [dir=none];
+        driver -> payload1;
+        driver -> payload2 [penwidth=3];
+        edge [dir=""];
+    }
+
+    /* Driver malloc references */
+    edge [style=dashed];
+    driver -> port1;
+    driver -> port2;
+    driver -> port3:e;
+    driver -> port4 [color=grey];
+    payload1:s -> port1:e;
+    payload2:s -> port3:e [penwidth=3];
+    edge [style=""];
+
+    subgraph cluster_topology {
+        label="Topology Manager";
+        labelloc=bottom;
+
+        /* Topology references */
+        mstb1 -> {port1, port2};
+        port1 -> mstb2;
+        edge [color=grey];
+        port2 -> mstb3 -> {port3, port4};
+        port3 -> mstb4;
+        edge [color=""];
+
+        /* Malloc references */
+        edge [style=dashed;dir=back];
+        mstb1 -> {port1, port2};
+        port1 -> mstb2;
+        port2 -> mstb3 [penwidth=3];
+        mstb3 -> port3 [penwidth=3];
+        edge [color=grey];
+        mstb3 -> port4;
+        port3 -> mstb4;
+    }
+
+    mstb1 [label="MSTB #1";style=filled;fillcolor=palegreen];
+    mstb2 [label="MSTB #2";style=filled;fillcolor=palegreen];
+    mstb3 [label="MSTB #3";style=filled;fillcolor=palegreen;penwidth=3];
+    mstb4 [label="MSTB #4";style=filled;fillcolor=grey];
+
+    port1 [label="Port #1"];
+    port2 [label="Port #2";penwidth=5];
+    port3 [label="Port #3";penwidth=3];
+    port4 [label="Port #4";style=filled;fillcolor=grey];
+
+    driver [label="DRM driver";style=filled;shape=box;fillcolor=lightblue];
+
+    payload1 [label="Payload #1";style=filled;shape=box;fillcolor=lightblue];
+    payload2 [label="Payload #2";style=filled;shape=box;fillcolor=lightblue;penwidth=3];
+}
diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst
index b422eb8edf16..7a3fc569bc68 100644
--- a/Documentation/gpu/drm-kms-helpers.rst
+++ b/Documentation/gpu/drm-kms-helpers.rst
@@ -208,18 +208,40 @@ Display Port Dual Mode Adaptor Helper Functions Reference
 .. kernel-doc:: drivers/gpu/drm/drm_dp_dual_mode_helper.c
    :export:
 
-Display Port MST Helper Functions Reference
-===========================================
+Display Port MST Helpers
+========================
+
+Overview
+--------
 
 .. kernel-doc:: drivers/gpu/drm/drm_dp_mst_topology.c
    :doc: dp mst helper
 
+.. kernel-doc:: drivers/gpu/drm/drm_dp_mst_topology.c
+   :doc: Branch device and port refcounting
+
+Functions Reference
+-------------------
+
 .. kernel-doc:: include/drm/drm_dp_mst_helper.h
    :internal:
 
 .. kernel-doc:: drivers/gpu/drm/drm_dp_mst_topology.c
    :export:
 
+Topology Lifetime Internals
+---------------------------
+
+These functions aren't exported to drivers, but are documented here to help make
+the MST topology helpers easier to understand
+
+.. kernel-doc:: drivers/gpu/drm/drm_dp_mst_topology.c
+   :functions: drm_dp_mst_topology_try_get_mstb drm_dp_mst_topology_get_mstb
+               drm_dp_mst_topology_put_mstb
+               drm_dp_mst_topology_try_get_port drm_dp_mst_topology_get_port
+               drm_dp_mst_topology_put_port
+               drm_dp_mst_get_mstb_malloc drm_dp_mst_put_mstb_malloc
+
 MIPI DSI Helper Functions Reference
 ===================================
 
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 074e985093ca..c53cf7eb1dbc 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -850,46 +850,211 @@ static struct drm_dp_mst_branch *drm_dp_add_mst_branch_device(u8 lct, u8 *rad)
 	if (lct > 1)
 		memcpy(mstb->rad, rad, lct / 2);
 	INIT_LIST_HEAD(&mstb->ports);
-	kref_init(&mstb->kref);
+	kref_init(&mstb->topology_kref);
+	kref_init(&mstb->malloc_kref);
 	return mstb;
 }
 
-static void drm_dp_free_mst_port(struct kref *kref);
-
 static void drm_dp_free_mst_branch_device(struct kref *kref)
 {
-	struct drm_dp_mst_branch *mstb = container_of(kref, struct drm_dp_mst_branch, kref);
-	if (mstb->port_parent) {
-		if (list_empty(&mstb->port_parent->next))
-			kref_put(&mstb->port_parent->kref, drm_dp_free_mst_port);
-	}
+	struct drm_dp_mst_branch *mstb =
+		container_of(kref, struct drm_dp_mst_branch, malloc_kref);
+
+	if (mstb->port_parent)
+		drm_dp_mst_put_port_malloc(mstb->port_parent);
+
 	kfree(mstb);
 }
 
+/**
+ * DOC: Branch device and port refcounting
+ *
+ * Topology refcount overview
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * The refcounting schemes for &struct drm_dp_mst_branch and &struct
+ * drm_dp_mst_port are somewhat unusual. Both ports and branch devices have
+ * two different kinds of refcounts: topology refcounts, and malloc refcounts.
+ *
+ * Topology refcounts are not exposed to drivers, and are handled internally
+ * by the DP MST helpers. The helpers use them in order to prevent the
+ * in-memory topology state from being changed in the middle of critical
+ * operations like changing the internal state of payload allocations. This
+ * means each branch and port will be considered to be connected to the rest
+ * of the topology until it's topology refcount reaches zero. Additionally,
+ * for ports this means that their associated &struct drm_connector will stay
+ * registered with userspace until the port's refcount reaches 0.
+ *
+ * Malloc refcount overview
+ * ~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * Malloc references are used to keep a &struct drm_dp_mst_port or &struct
+ * drm_dp_mst_branch allocated even after all of its topology references have
+ * been dropped, so that the driver or MST helpers can safely access each
+ * branch's last known state before it was disconnected from the topology.
+ * When the malloc refcount of a port or branch reaches 0, the memory
+ * allocation containing the &struct drm_dp_mst_branch or &struct
+ * drm_dp_mst_port respectively will be freed.
+ *
+ * For &struct drm_dp_mst_branch, malloc refcounts are not currently exposed
+ * to drivers. As of writing this documentation, there are no drivers that
+ * have a usecase for accessing &struct drm_dp_mst_branch outside of the MST
+ * helpers. Exposing this API to drivers in a race-free manner would take more
+ * tweaking of the refcounting scheme, however patches are welcome provided
+ * there is a legitimate driver usecase for this.
+ *
+ * Refcount relationships in a topology
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * Let's take a look at why the relationship between topology and malloc
+ * refcounts is designed the way it is.
+ *
+ * .. kernel-figure:: dp-mst/topology-figure-1.dot
+ *
+ *    An example of topology and malloc refs in a DP MST topology with two
+ *    active payloads. Topology refcount increments are indicated by solid
+ *    lines, and malloc refcount increments are indicated by dashed lines.
+ *    Each starts from the branch which incremented the refcount, and ends at
+ *    the branch to which the refcount belongs to.
+ *
+ * As you can see in figure 1, every branch increments the topology refcount
+ * of it's children, and increments the malloc refcount of it's parent.
+ * Additionally, every payload increments the malloc refcount of it's assigned
+ * port by 1.
+ *
+ * So, what would happen if MSTB #3 from the above figure was unplugged from
+ * the system, but the driver hadn't yet removed payload #2 from port #3? The
+ * topology would start to look like figure 2.
+ *
+ * .. kernel-figure:: dp-mst/topology-figure-2.dot
+ *
+ *    Ports and branch devices which have been released from memory are
+ *    colored grey, and references which have been removed are colored red.
+ *
+ * Whenever a port or branch device's topology refcount reaches zero, it will
+ * decrement the topology refcounts of all its children, the malloc refcount
+ * of its parent, and finally its own malloc refcount. For MSTB #4 and port
+ * #4, this means they both have been disconnected from the topology and freed
+ * from memory. But, because payload #2 is still holding a reference to port
+ * #3, port #3 is removed from the topology but it's &struct drm_dp_mst_port
+ * is still accessible from memory. This also means port #3 has not yet
+ * decremented the malloc refcount of MSTB #3, so it's &struct
+ * drm_dp_mst_branch will also stay allocated in memory until port #3's
+ * malloc refcount reaches 0.
+ *
+ * This relationship is necessary because in order to release payload #2, we
+ * need to be able to figure out the last relative of port #3 that's still
+ * connected to the topology. In this case, we would travel up the topology as
+ * shown in figure 3.
+ *
+ * .. kernel-figure:: dp-mst/topology-figure-3.dot
+ *
+ * And finally, remove payload #2 by communicating with port #2 through
+ * sideband transactions.
+ */
+
+/**
+ * drm_dp_mst_get_mstb_malloc() - Increment the malloc refcount of a branch
+ * device
+ * @mstb: The &struct drm_dp_mst_branch to increment the malloc refcount of
+ *
+ * Increments &drm_dp_mst_branch.malloc_kref. When
+ * &drm_dp_mst_branch.malloc_kref reaches 0, the memory allocation for @mstb
+ * will be released and @mstb may no longer be used.
+ *
+ * See also: drm_dp_mst_put_mstb_malloc()
+ */
+static void
+drm_dp_mst_get_mstb_malloc(struct drm_dp_mst_branch *mstb)
+{
+	kref_get(&mstb->malloc_kref);
+	DRM_DEBUG("mstb %p (%d)\n", mstb, kref_read(&mstb->malloc_kref));
+}
+
+/**
+ * drm_dp_mst_put_mstb_malloc() - Decrement the malloc refcount of a branch
+ * device
+ * @mstb: The &struct drm_dp_mst_branch to decrement the malloc refcount of
+ *
+ * Decrements &drm_dp_mst_branch.malloc_kref. When
+ * &drm_dp_mst_branch.malloc_kref reaches 0, the memory allocation for @mstb
+ * will be released and @mstb may no longer be used.
+ *
+ * See also: drm_dp_mst_get_mstb_malloc()
+ */
+static void
+drm_dp_mst_put_mstb_malloc(struct drm_dp_mst_branch *mstb)
+{
+	DRM_DEBUG("mstb %p (%d)\n", mstb, kref_read(&mstb->malloc_kref) - 1);
+	kref_put(&mstb->malloc_kref, drm_dp_free_mst_branch_device);
+}
+
+static void drm_dp_free_mst_port(struct kref *kref)
+{
+	struct drm_dp_mst_port *port =
+		container_of(kref, struct drm_dp_mst_port, malloc_kref);
+
+	drm_dp_mst_put_mstb_malloc(port->parent);
+	kfree(port);
+}
+
+/**
+ * drm_dp_mst_get_port_malloc() - Increment the malloc refcount of an MST port
+ * @port: The &struct drm_dp_mst_port to increment the malloc refcount of
+ *
+ * Increments &drm_dp_mst_port.malloc_kref. When &drm_dp_mst_port.malloc_kref
+ * reaches 0, the memory allocation for @port will be released and @port may
+ * no longer be used.
+ *
+ * Because @port could potentially be freed at any time by the DP MST helpers
+ * if &drm_dp_mst_port.malloc_kref reaches 0, including during a call to this
+ * function, drivers that which to make use of &struct drm_dp_mst_port should
+ * ensure that they grab at least one main malloc reference to their MST ports
+ * in &drm_dp_mst_topology_cbs.add_connector. This callback is called before
+ * there is any chance for &drm_dp_mst_port.malloc_kref to reach 0.
+ *
+ * See also: drm_dp_mst_put_port_malloc()
+ */
+void
+drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port)
+{
+	kref_get(&port->malloc_kref);
+	DRM_DEBUG("port %p (%d)\n", port, kref_read(&port->malloc_kref));
+}
+EXPORT_SYMBOL(drm_dp_mst_get_port_malloc);
+
+/**
+ * drm_dp_mst_put_port_malloc() - Decrement the malloc refcount of an MST port
+ * @port: The &struct drm_dp_mst_port to decrement the malloc refcount of
+ *
+ * Decrements &drm_dp_mst_port.malloc_kref. When &drm_dp_mst_port.malloc_kref
+ * reaches 0, the memory allocation for @port will be released and @port may
+ * no longer be used.
+ *
+ * See also: drm_dp_mst_get_port_malloc()
+ */
+void
+drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port)
+{
+	DRM_DEBUG("port %p (%d)\n", port, kref_read(&port->malloc_kref) - 1);
+	kref_put(&port->malloc_kref, drm_dp_free_mst_port);
+}
+EXPORT_SYMBOL(drm_dp_mst_put_port_malloc);
+
 static void drm_dp_destroy_mst_branch_device(struct kref *kref)
 {
-	struct drm_dp_mst_branch *mstb = container_of(kref, struct drm_dp_mst_branch, kref);
+	struct drm_dp_mst_branch *mstb =
+		container_of(kref, struct drm_dp_mst_branch, topology_kref);
+	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
 	struct drm_dp_mst_port *port, *tmp;
 	bool wake_tx = false;
 
-	/*
-	 * init kref again to be used by ports to remove mst branch when it is
-	 * not needed anymore
-	 */
-	kref_init(kref);
-
-	if (mstb->port_parent && list_empty(&mstb->port_parent->next))
-		kref_get(&mstb->port_parent->kref);
-
-	/*
-	 * destroy all ports - don't need lock
-	 * as there are no more references to the mst branch
-	 * device at this point.
-	 */
+	mutex_lock(&mgr->lock);
 	list_for_each_entry_safe(port, tmp, &mstb->ports, next) {
 		list_del(&port->next);
 		drm_dp_mst_topology_put_port(port);
 	}
+	mutex_unlock(&mgr->lock);
 
 	/* drop any tx slots msg */
 	mutex_lock(&mstb->mgr->qlock);
@@ -908,14 +1073,83 @@ static void drm_dp_destroy_mst_branch_device(struct kref *kref)
 	if (wake_tx)
 		wake_up_all(&mstb->mgr->tx_waitq);
 
-	kref_put(kref, drm_dp_free_mst_branch_device);
+	drm_dp_mst_put_mstb_malloc(mstb);
 }
 
-static void drm_dp_mst_topology_put_mstb(struct drm_dp_mst_branch *mstb)
+/**
+ * drm_dp_mst_topology_try_get_mstb() - Increment the topology refcount of a
+ * branch device unless its zero
+ * @mstb: &struct drm_dp_mst_branch to increment the topology refcount of
+ *
+ * Attempts to grab a topology reference to @mstb, if it hasn't yet been
+ * removed from the topology (e.g. &drm_dp_mst_branch.topology_kref has
+ * reached 0). Holding a topology reference implies that a malloc reference
+ * will be held to @mstb as long as the user holds the topology reference.
+ *
+ * Care should be taken to ensure that the user has at least one malloc
+ * reference to @mstb. If you already have a topology reference to @mstb, you
+ * should use drm_dp_mst_topology_get_mstb() instead.
+ *
+ * See also:
+ * drm_dp_mst_topology_get_mstb()
+ * drm_dp_mst_topology_put_mstb()
+ *
+ * Returns:
+ * * 1: A topology reference was grabbed successfully
+ * * 0: @port is no longer in the topology, no reference was grabbed
+ */
+static int __must_check
+drm_dp_mst_topology_try_get_mstb(struct drm_dp_mst_branch *mstb)
 {
-	kref_put(&mstb->kref, drm_dp_destroy_mst_branch_device);
+	int ret = kref_get_unless_zero(&mstb->topology_kref);
+
+	if (ret)
+		DRM_DEBUG("mstb %p (%d)\n", mstb,
+			  kref_read(&mstb->topology_kref));
+
+	return ret;
 }
 
+/**
+ * drm_dp_mst_topology_get_mstb() - Increment the topology refcount of a
+ * branch device
+ * @mstb: The &struct drm_dp_mst_branch to increment the topology refcount of
+ *
+ * Increments &drm_dp_mst_branch.topology_refcount without checking whether or
+ * not it's already reached 0. This is only valid to use in scenarios where
+ * you are already guaranteed to have at least one active topology reference
+ * to @mstb. Otherwise, drm_dp_mst_topology_try_get_mstb() must be used.
+ *
+ * See also:
+ * drm_dp_mst_topology_try_get_mstb()
+ * drm_dp_mst_topology_put_mstb()
+ */
+static void drm_dp_mst_topology_get_mstb(struct drm_dp_mst_branch *mstb)
+{
+	WARN_ON(kref_read(&mstb->topology_kref) == 0);
+	kref_get(&mstb->topology_kref);
+	DRM_DEBUG("mstb %p (%d)\n", mstb, kref_read(&mstb->topology_kref));
+}
+
+/**
+ * drm_dp_mst_topology_put_mstb() - release a topology reference to a branch
+ * device
+ * @mstb: The &struct drm_dp_mst_branch to release the topology reference from
+ *
+ * Releases a topology reference from @mstb by decrementing
+ * &drm_dp_mst_branch.topology_kref.
+ *
+ * See also:
+ * drm_dp_mst_topology_try_get_mstb()
+ * drm_dp_mst_topology_get_mstb()
+ */
+static void
+drm_dp_mst_topology_put_mstb(struct drm_dp_mst_branch *mstb)
+{
+	DRM_DEBUG("mstb %p (%d)\n",
+		  mstb, kref_read(&mstb->topology_kref) - 1);
+	kref_put(&mstb->topology_kref, drm_dp_destroy_mst_branch_device);
+}
 
 static void drm_dp_port_teardown_pdt(struct drm_dp_mst_port *port, int old_pdt)
 {
@@ -937,7 +1171,8 @@ static void drm_dp_port_teardown_pdt(struct drm_dp_mst_port *port, int old_pdt)
 
 static void drm_dp_destroy_port(struct kref *kref)
 {
-	struct drm_dp_mst_port *port = container_of(kref, struct drm_dp_mst_port, kref);
+	struct drm_dp_mst_port *port =
+		container_of(kref, struct drm_dp_mst_port, topology_kref);
 	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
 
 	if (!port->input) {
@@ -956,7 +1191,6 @@ static void drm_dp_destroy_port(struct kref *kref)
 			 * from an EDID retrieval */
 
 			mutex_lock(&mgr->destroy_connector_lock);
-			kref_get(&port->parent->kref);
 			list_add(&port->next, &mgr->destroy_connector_list);
 			mutex_unlock(&mgr->destroy_connector_lock);
 			schedule_work(&mgr->destroy_connector_work);
@@ -967,12 +1201,79 @@ static void drm_dp_destroy_port(struct kref *kref)
 		drm_dp_port_teardown_pdt(port, port->pdt);
 		port->pdt = DP_PEER_DEVICE_NONE;
 	}
-	kfree(port);
+	drm_dp_mst_put_port_malloc(port);
+}
+
+/**
+ * drm_dp_mst_topology_try_get_port() - Increment the topology refcount of a
+ * port unless its zero
+ * @port: &struct drm_dp_mst_port to increment the topology refcount of
+ *
+ * Attempts to grab a topology reference to @port, if it hasn't yet been
+ * removed from the topology (e.g. &drm_dp_mst_port.topology_kref has reached
+ * 0). Holding a topology reference implies that a malloc reference will be
+ * held to @port as long as the user holds the topology reference.
+ *
+ * Care should be taken to ensure that the user has at least one malloc
+ * reference to @port. If you already have a topology reference to @port, you
+ * should use drm_dp_mst_topology_get_port() instead.
+ *
+ * See also:
+ * drm_dp_mst_topology_get_port()
+ * drm_dp_mst_topology_put_port()
+ *
+ * Returns:
+ * * 1: A topology reference was grabbed successfully
+ * * 0: @port is no longer in the topology, no reference was grabbed
+ */
+static int __must_check
+drm_dp_mst_topology_try_get_port(struct drm_dp_mst_port *port)
+{
+	int ret = kref_get_unless_zero(&port->topology_kref);
+
+	if (ret)
+		DRM_DEBUG("port %p (%d)\n", port,
+			  kref_read(&port->topology_kref));
+
+	return ret;
 }
 
+/**
+ * drm_dp_mst_topology_get_port() - Increment the topology refcount of a port
+ * @port: The &struct drm_dp_mst_port to increment the topology refcount of
+ *
+ * Increments &drm_dp_mst_port.topology_refcount without checking whether or
+ * not it's already reached 0. This is only valid to use in scenarios where
+ * you are already guaranteed to have at least one active topology reference
+ * to @port. Otherwise, drm_dp_mst_topology_try_get_port() must be used.
+ *
+ * See also:
+ * drm_dp_mst_topology_try_get_port()
+ * drm_dp_mst_topology_put_port()
+ */
+static void drm_dp_mst_topology_get_port(struct drm_dp_mst_port *port)
+{
+	WARN_ON(kref_read(&port->topology_kref) == 0);
+	kref_get(&port->topology_kref);
+	DRM_DEBUG("port %p (%d)\n", port, kref_read(&port->topology_kref));
+}
+
+/**
+ * drm_dp_mst_topology_put_port() - release a topology reference to a port
+ * @port: The &struct drm_dp_mst_port to release the topology reference from
+ *
+ * Releases a topology reference from @port by decrementing
+ * &drm_dp_mst_port.topology_kref.
+ *
+ * See also:
+ * drm_dp_mst_topology_try_get_port()
+ * drm_dp_mst_topology_get_port()
+ */
 static void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port)
 {
-	kref_put(&port->kref, drm_dp_destroy_port);
+	DRM_DEBUG("port %p (%d)\n",
+		  port, kref_read(&port->topology_kref) - 1);
+	kref_put(&port->topology_kref, drm_dp_destroy_port);
 }
 
 static struct drm_dp_mst_branch *
@@ -981,10 +1282,10 @@ drm_dp_mst_topology_get_mstb_validated_locked(struct drm_dp_mst_branch *mstb,
 {
 	struct drm_dp_mst_port *port;
 	struct drm_dp_mst_branch *rmstb;
-	if (to_find == mstb) {
-		kref_get(&mstb->kref);
+
+	if (to_find == mstb)
 		return mstb;
-	}
+
 	list_for_each_entry(port, &mstb->ports, next) {
 		if (port->mstb) {
 			rmstb = drm_dp_mst_topology_get_mstb_validated_locked(
@@ -1001,25 +1302,32 @@ drm_dp_mst_topology_get_mstb_validated(struct drm_dp_mst_topology_mgr *mgr,
 				       struct drm_dp_mst_branch *mstb)
 {
 	struct drm_dp_mst_branch *rmstb = NULL;
+
 	mutex_lock(&mgr->lock);
-	if (mgr->mst_primary)
+	if (mgr->mst_primary) {
 		rmstb = drm_dp_mst_topology_get_mstb_validated_locked(
 		    mgr->mst_primary, mstb);
+
+		if (rmstb && !drm_dp_mst_topology_try_get_mstb(rmstb))
+			rmstb = NULL;
+	}
 	mutex_unlock(&mgr->lock);
 	return rmstb;
 }
 
-static struct drm_dp_mst_port *drm_dp_mst_get_port_ref_locked(struct drm_dp_mst_branch *mstb, struct drm_dp_mst_port *to_find)
+static struct drm_dp_mst_port *
+drm_dp_mst_topology_get_port_validated_locked(struct drm_dp_mst_branch *mstb,
+					      struct drm_dp_mst_port *to_find)
 {
 	struct drm_dp_mst_port *port, *mport;
 
 	list_for_each_entry(port, &mstb->ports, next) {
-		if (port == to_find) {
-			kref_get(&port->kref);
+		if (port == to_find)
 			return port;
-		}
+
 		if (port->mstb) {
-			mport = drm_dp_mst_get_port_ref_locked(port->mstb, to_find);
+			mport = drm_dp_mst_topology_get_port_validated_locked(
+			    port->mstb, to_find);
 			if (mport)
 				return mport;
 		}
@@ -1032,9 +1340,15 @@ drm_dp_mst_topology_get_port_validated(struct drm_dp_mst_topology_mgr *mgr,
 				       struct drm_dp_mst_port *port)
 {
 	struct drm_dp_mst_port *rport = NULL;
+
 	mutex_lock(&mgr->lock);
-	if (mgr->mst_primary)
-		rport = drm_dp_mst_get_port_ref_locked(mgr->mst_primary, port);
+	if (mgr->mst_primary) {
+		rport = drm_dp_mst_topology_get_port_validated_locked(
+		    mgr->mst_primary, port);
+
+		if (rport && !drm_dp_mst_topology_try_get_port(rport))
+			rport = NULL;
+	}
 	mutex_unlock(&mgr->lock);
 	return rport;
 }
@@ -1042,11 +1356,12 @@ drm_dp_mst_topology_get_port_validated(struct drm_dp_mst_topology_mgr *mgr,
 static struct drm_dp_mst_port *drm_dp_get_port(struct drm_dp_mst_branch *mstb, u8 port_num)
 {
 	struct drm_dp_mst_port *port;
+	int ret;
 
 	list_for_each_entry(port, &mstb->ports, next) {
 		if (port->port_num == port_num) {
-			kref_get(&port->kref);
-			return port;
+			ret = drm_dp_mst_topology_try_get_port(port);
+			return ret ? port : NULL;
 		}
 	}
 
@@ -1095,6 +1410,11 @@ static bool drm_dp_port_setup_pdt(struct drm_dp_mst_port *port)
 		if (port->mstb) {
 			port->mstb->mgr = port->mgr;
 			port->mstb->port_parent = port;
+			/*
+			 * Make sure this port's memory allocation stays
+			 * around until it's child MSTB releases it
+			 */
+			drm_dp_mst_get_port_malloc(port);
 
 			send_link = true;
 		}
@@ -1155,17 +1475,26 @@ static void drm_dp_add_port(struct drm_dp_mst_branch *mstb,
 	bool created = false;
 	int old_pdt = 0;
 	int old_ddps = 0;
+
 	port = drm_dp_get_port(mstb, port_msg->port_number);
 	if (!port) {
 		port = kzalloc(sizeof(*port), GFP_KERNEL);
 		if (!port)
 			return;
-		kref_init(&port->kref);
+		kref_init(&port->topology_kref);
+		kref_init(&port->malloc_kref);
 		port->parent = mstb;
 		port->port_num = port_msg->port_number;
 		port->mgr = mstb->mgr;
 		port->aux.name = "DPMST";
 		port->aux.dev = dev->dev;
+
+		/*
+		 * Make sure the memory allocation for our parent branch stays
+		 * around until our own memory allocation is released
+		 */
+		drm_dp_mst_get_mstb_malloc(mstb);
+
 		created = true;
 	} else {
 		old_pdt = port->pdt;
@@ -1185,7 +1514,7 @@ static void drm_dp_add_port(struct drm_dp_mst_branch *mstb,
 	   for this list */
 	if (created) {
 		mutex_lock(&mstb->mgr->lock);
-		kref_get(&port->kref);
+		drm_dp_mst_topology_get_port(port);
 		list_add(&port->next, &mstb->ports);
 		mutex_unlock(&mstb->mgr->lock);
 	}
@@ -1284,7 +1613,7 @@ static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_
 {
 	struct drm_dp_mst_branch *mstb;
 	struct drm_dp_mst_port *port;
-	int i;
+	int i, ret;
 	/* find the port by iterating down */
 
 	mutex_lock(&mgr->lock);
@@ -1309,7 +1638,9 @@ static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_
 			}
 		}
 	}
-	kref_get(&mstb->kref);
+	ret = drm_dp_mst_topology_try_get_mstb(mstb);
+	if (!ret)
+		mstb = NULL;
 out:
 	mutex_unlock(&mgr->lock);
 	return mstb;
@@ -1344,14 +1675,17 @@ drm_dp_get_mst_branch_device_by_guid(struct drm_dp_mst_topology_mgr *mgr,
 				     uint8_t *guid)
 {
 	struct drm_dp_mst_branch *mstb;
+	int ret;
 
 	/* find the port by iterating down */
 	mutex_lock(&mgr->lock);
 
 	mstb = get_mst_branch_device_by_guid_helper(mgr->mst_primary, guid);
-
-	if (mstb)
-		kref_get(&mstb->kref);
+	if (mstb) {
+		ret = drm_dp_mst_topology_try_get_mstb(mstb);
+		if (!ret)
+			mstb = NULL;
+	}
 
 	mutex_unlock(&mgr->lock);
 	return mstb;
@@ -1390,11 +1724,14 @@ static void drm_dp_mst_link_probe_work(struct work_struct *work)
 {
 	struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct drm_dp_mst_topology_mgr, work);
 	struct drm_dp_mst_branch *mstb;
+	int ret;
 
 	mutex_lock(&mgr->lock);
 	mstb = mgr->mst_primary;
 	if (mstb) {
-		kref_get(&mstb->kref);
+		ret = drm_dp_mst_topology_try_get_mstb(mstb);
+		if (!ret)
+			mstb = NULL;
 	}
 	mutex_unlock(&mgr->lock);
 	if (mstb) {
@@ -1722,8 +2059,10 @@ static struct drm_dp_mst_branch *drm_dp_get_last_connected_port_and_mstb(struct
 
 		if (found_port) {
 			rmstb = found_port->parent;
-			kref_get(&rmstb->kref);
-			*port_num = found_port->port_num;
+			if (drm_dp_mst_topology_try_get_mstb(rmstb))
+				*port_num = found_port->port_num;
+			else
+				rmstb = NULL;
 		}
 	}
 	mutex_unlock(&mgr->lock);
@@ -2176,7 +2515,7 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
 
 		/* give this the main reference */
 		mgr->mst_primary = mstb;
-		kref_get(&mgr->mst_primary->kref);
+		drm_dp_mst_topology_get_mstb(mgr->mst_primary);
 
 		ret = drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
 							 DP_MST_EN | DP_UP_REQ_EN | DP_UPSTREAM_IS_SRC);
@@ -3096,13 +3435,6 @@ static void drm_dp_tx_work(struct work_struct *work)
 	mutex_unlock(&mgr->qlock);
 }
 
-static void drm_dp_free_mst_port(struct kref *kref)
-{
-	struct drm_dp_mst_port *port = container_of(kref, struct drm_dp_mst_port, kref);
-	kref_put(&port->parent->kref, drm_dp_free_mst_branch_device);
-	kfree(port);
-}
-
 static void drm_dp_destroy_connector_work(struct work_struct *work)
 {
 	struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct drm_dp_mst_topology_mgr, destroy_connector_work);
@@ -3123,7 +3455,6 @@ static void drm_dp_destroy_connector_work(struct work_struct *work)
 		list_del(&port->next);
 		mutex_unlock(&mgr->destroy_connector_lock);
 
-		kref_init(&port->kref);
 		INIT_LIST_HEAD(&port->next);
 
 		mgr->cbs->destroy_connector(mgr, port->connector);
@@ -3137,7 +3468,7 @@ static void drm_dp_destroy_connector_work(struct work_struct *work)
 			drm_dp_mst_put_payload_id(mgr, port->vcpi.vcpi);
 		}
 
-		kref_put(&port->kref, drm_dp_free_mst_port);
+		drm_dp_mst_put_port_malloc(port);
 		send_hotplug = true;
 	}
 	if (send_hotplug)
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 371cc2816477..8eca5f29242c 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -44,7 +44,6 @@ struct drm_dp_vcpi {
 
 /**
  * struct drm_dp_mst_port - MST port
- * @kref: reference count for this port.
  * @port_num: port number
  * @input: if this port is an input port.
  * @mcs: message capability status - DP 1.2 spec.
@@ -67,7 +66,18 @@ struct drm_dp_vcpi {
  * in the MST topology.
  */
 struct drm_dp_mst_port {
-	struct kref kref;
+	/**
+	 * @topology_kref: refcount for this port's lifetime in the topology,
+	 * only the DP MST helpers should need to touch this
+	 */
+	struct kref topology_kref;
+
+	/**
+	 * @malloc_kref: refcount for the memory allocation containing this
+	 * structure. See drm_dp_mst_get_port_malloc() and
+	 * drm_dp_mst_put_port_malloc().
+	 */
+	struct kref malloc_kref;
 
 	u8 port_num;
 	bool input;
@@ -102,7 +112,6 @@ struct drm_dp_mst_port {
 
 /**
  * struct drm_dp_mst_branch - MST branch device.
- * @kref: reference count for this port.
  * @rad: Relative Address to talk to this branch device.
  * @lct: Link count total to talk to this branch device.
  * @num_ports: number of ports on the branch.
@@ -121,7 +130,19 @@ struct drm_dp_mst_port {
  * to downstream port of parent branches.
  */
 struct drm_dp_mst_branch {
-	struct kref kref;
+	/**
+	 * @topology_kref: refcount for this branch device's lifetime in the
+	 * topology, only the DP MST helpers should need to touch this
+	 */
+	struct kref topology_kref;
+
+	/**
+	 * @malloc_kref: refcount for the memory allocation containing this
+	 * structure. See drm_dp_mst_get_mstb_malloc() and
+	 * drm_dp_mst_put_mstb_malloc().
+	 */
+	struct kref malloc_kref;
+
 	u8 rad[8];
 	u8 lct;
 	int num_ports;
@@ -626,4 +647,7 @@ int drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
 int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
 				 struct drm_dp_mst_port *port, bool power_up);
 
+void drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port);
+void drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port);
+
 #endif
-- 
2.20.1

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[PATCH v5 07/20] drm/dp_mst: Restart last_connected_port_and_mstb() if topology ref fails

[Lyude Paul]

While this isn't a complete fix, this will improve the reliability of
drm_dp_get_last_connected_port_and_mstb() pretty significantly during
hotplug events, since there's a chance that the in-memory topology tree
may not be fully updated when drm_dp_get_last_connected_port_and_mstb()
is called and thus might end up causing our search to fail on an mstb
whose topology refcount has reached 0, but has not yet been removed from
it's parent.

Ideally, we should further fix this problem by ensuring that we deal
with the potential for racing with a hotplug event, which would look
like this:

* drm_dp_payload_send_msg() retrieves the last living relative of mstb
  with drm_dp_get_last_connected_port_and_mstb()
* drm_dp_payload_send_msg() starts building payload message
  At the same time, mstb gets unplugged from the topology and is no
  longer the actual last living relative of the original mstb
* drm_dp_payload_send_msg() tries sending the payload message, hub times
  out
* Hub timed out, we give up and run away-resulting in the payload being
  leaked

This could be fixed by restarting the
drm_dp_get_last_connected_port_and_mstb() search whenever we get a
timeout, sending the payload to the new mstb, then repeating until
either the entire topology is removed from the system or
drm_dp_get_last_connected_port_and_mstb() fails. But since the above
race condition is not terribly likely, we'll address that in a later
patch series once we've improved the recovery handling for VCPI
allocations in the rest of the DP MST helpers.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 54 ++++++++++++++++++++++-----
 1 file changed, 44 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index c53cf7eb1dbc..bafc85f08606 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2047,24 +2047,50 @@ static struct drm_dp_mst_port *drm_dp_get_last_connected_port_to_mstb(struct drm
 	return drm_dp_get_last_connected_port_to_mstb(mstb->port_parent->parent);
 }
 
-static struct drm_dp_mst_branch *drm_dp_get_last_connected_port_and_mstb(struct drm_dp_mst_topology_mgr *mgr,
-									 struct drm_dp_mst_branch *mstb,
-									 int *port_num)
+/**
+ * drm_dp_get_last_connected_port_and_mstb() - Find the last living relatives
+ * in a topology of a given branch device
+ * @mgr: The topology manager to use
+ * @mstb: The disconnected branch device
+ * @port_num: Where to store the number of the last connected port
+ *
+ * Searches upwards in the topology starting from @mstb to try to find the
+ * closest available parent of @mstb that's still connected to the rest of the
+ * topology. This can be used in order to perform operations like releasing
+ * payloads, where the branch device which owned the payload may no longer be
+ * around and thus would require that the payload on the last living relative
+ * be freed instead.
+ *
+ * Returns:
+ * The last connected &drm_dp_mst_branch in the topology that was a parent of
+ * @mstb, if there is one.
+ */
+static struct drm_dp_mst_branch *
+drm_dp_get_last_connected_port_and_mstb(struct drm_dp_mst_topology_mgr *mgr,
+					struct drm_dp_mst_branch *mstb,
+					int *port_num)
 {
 	struct drm_dp_mst_branch *rmstb = NULL;
 	struct drm_dp_mst_port *found_port;
+
 	mutex_lock(&mgr->lock);
-	if (mgr->mst_primary) {
+	if (!mgr->mst_primary)
+		goto out;
+
+	do {
 		found_port = drm_dp_get_last_connected_port_to_mstb(mstb);
+		if (!found_port)
+			break;
 
-		if (found_port) {
+		if (drm_dp_mst_topology_try_get_mstb(found_port->parent)) {
 			rmstb = found_port->parent;
-			if (drm_dp_mst_topology_try_get_mstb(rmstb))
-				*port_num = found_port->port_num;
-			else
-				rmstb = NULL;
+			*port_num = found_port->port_num;
+		} else {
+			/* Search again, starting from this parent */
+			mstb = found_port->parent;
 		}
-	}
+	} while (!rmstb);
+out:
 	mutex_unlock(&mgr->lock);
 	return rmstb;
 }
@@ -2113,6 +2139,14 @@ static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
 
 	drm_dp_queue_down_tx(mgr, txmsg);
 
+	/*
+	 * FIXME: there is a small chance that between getting the last
+	 * connected mstb and sending the payload message, the last connected
+	 * mstb could also be removed from the topology. In the future, this
+	 * needs to be fixed by restarting the
+	 * drm_dp_get_last_connected_port_and_mstb() search in the event of a
+	 * timeout if the topology is still connected to the system.
+	 */
 	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
 	if (ret > 0) {
 		if (txmsg->reply.reply_type == 1)
-- 
2.20.1

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[PATCH v5 08/20] drm/dp_mst: Stop releasing VCPI when removing ports from topology

[Lyude Paul]

This has never actually worked, and isn't needed anyway: the driver's
always going to try to deallocate VCPI when it tears down the display
that the VCPI belongs to.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index bafc85f08606..8088527a7aea 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1176,8 +1176,6 @@ static void drm_dp_destroy_port(struct kref *kref)
 	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
 
 	if (!port->input) {
-		port->vcpi.num_slots = 0;
-
 		kfree(port->cached_edid);
 
 		/*
@@ -3496,12 +3494,6 @@ static void drm_dp_destroy_connector_work(struct work_struct *work)
 		drm_dp_port_teardown_pdt(port, port->pdt);
 		port->pdt = DP_PEER_DEVICE_NONE;
 
-		if (!port->input && port->vcpi.vcpi > 0) {
-			drm_dp_mst_reset_vcpi_slots(mgr, port);
-			drm_dp_update_payload_part1(mgr);
-			drm_dp_mst_put_payload_id(mgr, port->vcpi.vcpi);
-		}
-
 		drm_dp_mst_put_port_malloc(port);
 		send_hotplug = true;
 	}
-- 
2.20.1

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[PATCH v5 09/20] drm/dp_mst: Fix payload deallocation on hotplugs using malloc refs

[Lyude Paul]

Up until now, freeing payloads on remote MST hubs that just had ports
removed has almost never worked because we've been relying on port
validation in order to stop us from accessing ports that have already
been freed from memory, but ports which need their payloads released due
to being removed will never be a valid part of the topology after
they've been removed.

Since we've introduced malloc refs, we can replace all of the validation
logic in payload helpers which are used for deallocation with some
well-placed malloc krefs. This ensures that regardless of whether or not
the ports are still valid and in the topology, any port which has an
allocated payload will remain allocated in memory until it's payloads
have been removed - finally allowing us to actually release said
payloads correctly.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 54 +++++++++++++++------------
 1 file changed, 30 insertions(+), 24 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 8088527a7aea..efd8fa29fff6 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2104,10 +2104,6 @@ static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
 	u8 sinks[DRM_DP_MAX_SDP_STREAMS];
 	int i;
 
-	port = drm_dp_mst_topology_get_port_validated(mgr, port);
-	if (!port)
-		return -EINVAL;
-
 	port_num = port->port_num;
 	mstb = drm_dp_mst_topology_get_mstb_validated(mgr, port->parent);
 	if (!mstb) {
@@ -2115,10 +2111,8 @@ static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
 							       port->parent,
 							       &port_num);
 
-		if (!mstb) {
-			drm_dp_mst_topology_put_port(port);
+		if (!mstb)
 			return -EINVAL;
-		}
 	}
 
 	txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
@@ -2155,7 +2149,6 @@ static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
 	kfree(txmsg);
 fail_put:
 	drm_dp_mst_topology_put_mstb(mstb);
-	drm_dp_mst_topology_put_port(port);
 	return ret;
 }
 
@@ -2260,15 +2253,16 @@ static int drm_dp_destroy_payload_step2(struct drm_dp_mst_topology_mgr *mgr,
  */
 int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr)
 {
-	int i, j;
-	int cur_slots = 1;
 	struct drm_dp_payload req_payload;
 	struct drm_dp_mst_port *port;
+	int i, j;
+	int cur_slots = 1;
 
 	mutex_lock(&mgr->payload_lock);
 	for (i = 0; i < mgr->max_payloads; i++) {
 		struct drm_dp_vcpi *vcpi = mgr->proposed_vcpis[i];
 		struct drm_dp_payload *payload = &mgr->payloads[i];
+		bool put_port = false;
 
 		/* solve the current payloads - compare to the hw ones
 		   - update the hw view */
@@ -2276,12 +2270,20 @@ int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr)
 		if (vcpi) {
 			port = container_of(vcpi, struct drm_dp_mst_port,
 					    vcpi);
-			port = drm_dp_mst_topology_get_port_validated(mgr,
-								      port);
-			if (!port) {
-				mutex_unlock(&mgr->payload_lock);
-				return -EINVAL;
+
+			/* Validated ports don't matter if we're releasing
+			 * VCPI
+			 */
+			if (vcpi->num_slots) {
+				port = drm_dp_mst_topology_get_port_validated(
+				    mgr, port);
+				if (!port) {
+					mutex_unlock(&mgr->payload_lock);
+					return -EINVAL;
+				}
+				put_port = true;
 			}
+
 			req_payload.num_slots = vcpi->num_slots;
 			req_payload.vcpi = vcpi->vcpi;
 		} else {
@@ -2313,7 +2315,7 @@ int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr)
 		}
 		cur_slots += req_payload.num_slots;
 
-		if (port)
+		if (put_port)
 			drm_dp_mst_topology_put_port(port);
 	}
 
@@ -3129,6 +3131,8 @@ bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 	DRM_DEBUG_KMS("initing vcpi for pbn=%d slots=%d\n",
 		      pbn, port->vcpi.num_slots);
 
+	/* Keep port allocated until it's payload has been removed */
+	drm_dp_mst_get_port_malloc(port);
 	drm_dp_mst_topology_put_port(port);
 	return true;
 out:
@@ -3158,11 +3162,12 @@ EXPORT_SYMBOL(drm_dp_mst_get_vcpi_slots);
  */
 void drm_dp_mst_reset_vcpi_slots(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port)
 {
-	port = drm_dp_mst_topology_get_port_validated(mgr, port);
-	if (!port)
-		return;
+	/*
+	 * A port with VCPI will remain allocated until it's VCPI is
+	 * released, no verified ref needed
+	 */
+
 	port->vcpi.num_slots = 0;
-	drm_dp_mst_topology_put_port(port);
 }
 EXPORT_SYMBOL(drm_dp_mst_reset_vcpi_slots);
 
@@ -3174,16 +3179,17 @@ EXPORT_SYMBOL(drm_dp_mst_reset_vcpi_slots);
 void drm_dp_mst_deallocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 				struct drm_dp_mst_port *port)
 {
-	port = drm_dp_mst_topology_get_port_validated(mgr, port);
-	if (!port)
-		return;
+	/*
+	 * A port with VCPI will remain allocated until it's VCPI is
+	 * released, no verified ref needed
+	 */
 
 	drm_dp_mst_put_payload_id(mgr, port->vcpi.vcpi);
 	port->vcpi.num_slots = 0;
 	port->vcpi.pbn = 0;
 	port->vcpi.aligned_pbn = 0;
 	port->vcpi.vcpi = 0;
-	drm_dp_mst_topology_put_port(port);
+	drm_dp_mst_put_port_malloc(port);
 }
 EXPORT_SYMBOL(drm_dp_mst_deallocate_vcpi);
 
-- 
2.20.1

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[PATCH v5 10/20] drm/i915: Keep malloc references to MST ports

[Lyude Paul]

So that the ports stay around until we've destroyed the connectors, in
order to ensure that we don't pass an invalid pointer to any MST helpers
once we introduce the new MST VCPI helpers.

Changes since v1:
* Move drm_dp_mst_get_port_malloc() to where we assign
  intel_connector->port - danvet

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/i915/intel_connector.c | 4 ++++
 drivers/gpu/drm/i915/intel_dp_mst.c    | 1 +
 2 files changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_connector.c b/drivers/gpu/drm/i915/intel_connector.c
index 18e370f607bc..37d2c644f4b8 100644
--- a/drivers/gpu/drm/i915/intel_connector.c
+++ b/drivers/gpu/drm/i915/intel_connector.c
@@ -95,6 +95,10 @@ void intel_connector_destroy(struct drm_connector *connector)
 	intel_panel_fini(&intel_connector->panel);
 
 	drm_connector_cleanup(connector);
+
+	if (intel_connector->port)
+		drm_dp_mst_put_port_malloc(intel_connector->port);
+
 	kfree(connector);
 }
 
diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
index f05427b74e34..631fd1537252 100644
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -457,6 +457,7 @@ static struct drm_connector *intel_dp_add_mst_connector(struct drm_dp_mst_topolo
 	intel_connector->get_hw_state = intel_dp_mst_get_hw_state;
 	intel_connector->mst_port = intel_dp;
 	intel_connector->port = port;
+	drm_dp_mst_get_port_malloc(port);
 
 	connector = &intel_connector->base;
 	ret = drm_connector_init(dev, connector, &intel_dp_mst_connector_funcs,
-- 
2.20.1

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[PATCH v5 11/20] drm/amdgpu/display: Keep malloc ref to MST port

[Lyude Paul]

Just like i915 and nouveau, it's a good idea for us to hold a malloc
reference to the port here so that we never pass a freed pointer to any
of the DP MST helper functions.

Also, we stop unsetting aconnector->port in
dm_dp_destroy_mst_connector(). There's literally no point to that
assignment that I can see anyway.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 .../drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c   | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
index 5e7ca1f3a8d1..24632727e127 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
@@ -191,6 +191,7 @@ dm_dp_mst_connector_destroy(struct drm_connector *connector)
 	drm_encoder_cleanup(&amdgpu_encoder->base);
 	kfree(amdgpu_encoder);
 	drm_connector_cleanup(connector);
+	drm_dp_mst_put_port_malloc(amdgpu_dm_connector->port);
 	kfree(amdgpu_dm_connector);
 }
 
@@ -363,7 +364,9 @@ dm_dp_add_mst_connector(struct drm_dp_mst_topology_mgr *mgr,
 	amdgpu_dm_connector_funcs_reset(connector);
 
 	DRM_INFO("DM_MST: added connector: %p [id: %d] [master: %p]\n",
-			aconnector, connector->base.id, aconnector->mst_port);
+		 aconnector, connector->base.id, aconnector->mst_port);
+
+	drm_dp_mst_get_port_malloc(port);
 
 	DRM_DEBUG_KMS(":%d\n", connector->base.id);
 
@@ -379,12 +382,12 @@ static void dm_dp_destroy_mst_connector(struct drm_dp_mst_topology_mgr *mgr,
 	struct amdgpu_dm_connector *aconnector = to_amdgpu_dm_connector(connector);
 
 	DRM_INFO("DM_MST: Disabling connector: %p [id: %d] [master: %p]\n",
-				aconnector, connector->base.id, aconnector->mst_port);
+		 aconnector, connector->base.id, aconnector->mst_port);
 
-	aconnector->port = NULL;
 	if (aconnector->dc_sink) {
 		amdgpu_dm_update_freesync_caps(connector, NULL);
-		dc_link_remove_remote_sink(aconnector->dc_link, aconnector->dc_sink);
+		dc_link_remove_remote_sink(aconnector->dc_link,
+					   aconnector->dc_sink);
 		dc_sink_release(aconnector->dc_sink);
 		aconnector->dc_sink = NULL;
 	}
-- 
2.20.1

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[PATCH v5 12/20] drm/nouveau: Remove bogus cleanup in nv50_mstm_add_connector()

[Lyude Paul]

Trying to destroy the connector using mstc->connector.funcs->destroy()
if connector initialization fails is wrong: there is no possible
codepath in nv50_mstc_new where nv50_mstm_add_connector() would return
<0 and mstc would be non-NULL.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 26af45785939..641252208e67 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -1099,11 +1099,8 @@ nv50_mstm_add_connector(struct drm_dp_mst_topology_mgr *mgr,
 	int ret;
 
 	ret = nv50_mstc_new(mstm, port, path, &mstc);
-	if (ret) {
-		if (mstc)
-			mstc->connector.funcs->destroy(&mstc->connector);
+	if (ret)
 		return NULL;
-	}
 
 	return &mstc->connector;
 }
-- 
2.20.1

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[PATCH v5 13/20] drm/nouveau: Remove unnecessary VCPI checks in nv50_msto_cleanup()

[Lyude Paul]

There is no need to look at the port's VCPI allocation before calling
drm_dp_mst_deallocate_vcpi(), as we already have msto->disabled to let
us avoid cleaning up an msto more then once. The DP MST core will never
call drm_dp_mst_deallocate_vcpi() on it's own, which is presumably what
these checks are meant to protect against.

More importantly though, we're about to stop clearing mstc->port in the
next commit, which means if we could potentially hit a use-after-free
error if we tried to check mstc->port->vcpi here. So to make life easier
for anyone who bisects this code in the future, use msto->disabled
instead to check whether or not we need to deallocate VCPI instead.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 641252208e67..0f7d72518604 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -704,14 +704,17 @@ nv50_msto_cleanup(struct nv50_msto *msto)
 	struct nv50_mstc *mstc = msto->mstc;
 	struct nv50_mstm *mstm = mstc->mstm;
 
+	if (!msto->disabled)
+		return;
+
 	NV_ATOMIC(drm, "%s: msto cleanup\n", msto->encoder.name);
-	if (mstc->port && mstc->port->vcpi.vcpi > 0 && !nv50_msto_payload(msto))
+
+	if (mstc->port)
 		drm_dp_mst_deallocate_vcpi(&mstm->mgr, mstc->port);
-	if (msto->disabled) {
-		msto->mstc = NULL;
-		msto->head = NULL;
-		msto->disabled = false;
-	}
+
+	msto->mstc = NULL;
+	msto->head = NULL;
+	msto->disabled = false;
 }
 
 static void
-- 
2.20.1

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[PATCH v5 14/20] drm/nouveau: Keep malloc references to MST ports

[Lyude Paul]

Now that we finally have a sane way to keep port allocations around, use
it to fix the potential unchecked ->port accesses that nouveau makes by
making sure we keep the mst port allocated for as long as it's
drm_connector is accessible.

Additionally, now that we've guaranteed that mstc->port is allocated for
as long as we keep mstc around we can remove the connector registration
checks for codepaths which release payloads, allowing us to release
payloads on active topologies properly. These registration checks were
only required before in order to avoid situations where mstc->port could
technically be pointing at freed memory.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 0f7d72518604..982054bbcc8b 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -964,7 +964,11 @@ static void
 nv50_mstc_destroy(struct drm_connector *connector)
 {
 	struct nv50_mstc *mstc = nv50_mstc(connector);
+
 	drm_connector_cleanup(&mstc->connector);
+	if (mstc->port)
+		drm_dp_mst_put_port_malloc(mstc->port);
+
 	kfree(mstc);
 }
 
@@ -1012,6 +1016,7 @@ nv50_mstc_new(struct nv50_mstm *mstm, struct drm_dp_mst_port *port,
 	drm_object_attach_property(&mstc->connector.base, dev->mode_config.path_property, 0);
 	drm_object_attach_property(&mstc->connector.base, dev->mode_config.tile_property, 0);
 	drm_connector_set_path_property(&mstc->connector, path);
+	drm_dp_mst_get_port_malloc(port);
 	return 0;
 }
 
@@ -1077,6 +1082,7 @@ nv50_mstm_destroy_connector(struct drm_dp_mst_topology_mgr *mgr,
 	drm_fb_helper_remove_one_connector(&drm->fbcon->helper, &mstc->connector);
 
 	drm_modeset_lock(&drm->dev->mode_config.connection_mutex, NULL);
+	drm_dp_mst_put_port_malloc(mstc->port);
 	mstc->port = NULL;
 	drm_modeset_unlock(&drm->dev->mode_config.connection_mutex);
 
-- 
2.20.1

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[PATCH v5 15/20] drm/nouveau: Stop unsetting mstc->port, use malloc refs

[Lyude Paul]

Same as we did for i915, but for nouveau this time. Additionally, we
grab a malloc reference to the port that lasts for the entire lifetime
of nv50_mstc, which gives us the guarantee that mstc->port will always
point to valid memory for as long as the mstc stays around.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c | 18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 982054bbcc8b..157d208d37b5 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -709,8 +709,7 @@ nv50_msto_cleanup(struct nv50_msto *msto)
 
 	NV_ATOMIC(drm, "%s: msto cleanup\n", msto->encoder.name);
 
-	if (mstc->port)
-		drm_dp_mst_deallocate_vcpi(&mstm->mgr, mstc->port);
+	drm_dp_mst_deallocate_vcpi(&mstm->mgr, mstc->port);
 
 	msto->mstc = NULL;
 	msto->head = NULL;
@@ -735,7 +734,7 @@ nv50_msto_prepare(struct nv50_msto *msto)
 	};
 
 	NV_ATOMIC(drm, "%s: msto prepare\n", msto->encoder.name);
-	if (mstc->port && mstc->port->vcpi.vcpi > 0) {
+	if (mstc->port->vcpi.vcpi > 0) {
 		struct drm_dp_payload *payload = nv50_msto_payload(msto);
 		if (payload) {
 			args.vcpi.start_slot = payload->start_slot;
@@ -832,8 +831,7 @@ nv50_msto_disable(struct drm_encoder *encoder)
 	struct nv50_mstc *mstc = msto->mstc;
 	struct nv50_mstm *mstm = mstc->mstm;
 
-	if (mstc->port)
-		drm_dp_mst_reset_vcpi_slots(&mstm->mgr, mstc->port);
+	drm_dp_mst_reset_vcpi_slots(&mstm->mgr, mstc->port);
 
 	mstm->outp->update(mstm->outp, msto->head->base.index, NULL, 0, 0);
 	mstm->modified = true;
@@ -945,7 +943,7 @@ nv50_mstc_detect(struct drm_connector *connector, bool force)
 	enum drm_connector_status conn_status;
 	int ret;
 
-	if (!mstc->port)
+	if (drm_connector_is_unregistered(connector))
 		return connector_status_disconnected;
 
 	ret = pm_runtime_get_sync(connector->dev->dev);
@@ -966,8 +964,7 @@ nv50_mstc_destroy(struct drm_connector *connector)
 	struct nv50_mstc *mstc = nv50_mstc(connector);
 
 	drm_connector_cleanup(&mstc->connector);
-	if (mstc->port)
-		drm_dp_mst_put_port_malloc(mstc->port);
+	drm_dp_mst_put_port_malloc(mstc->port);
 
 	kfree(mstc);
 }
@@ -1081,11 +1078,6 @@ nv50_mstm_destroy_connector(struct drm_dp_mst_topology_mgr *mgr,
 
 	drm_fb_helper_remove_one_connector(&drm->fbcon->helper, &mstc->connector);
 
-	drm_modeset_lock(&drm->dev->mode_config.connection_mutex, NULL);
-	drm_dp_mst_put_port_malloc(mstc->port);
-	mstc->port = NULL;
-	drm_modeset_unlock(&drm->dev->mode_config.connection_mutex);
-
 	drm_connector_put(&mstc->connector);
 }
 
-- 
2.20.1

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[PATCH v5 16/20] drm/nouveau: Grab payload lock in nv50_msto_payload()

[Lyude Paul]

Going through the currently programmed payloads isn't safe without
holding mgr->payload_lock, so actually do that and warn if anyone tries
calling nv50_msto_payload() in the future without grabbing the right
locks.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 157d208d37b5..67f7bf97e5d9 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -680,6 +680,8 @@ nv50_msto_payload(struct nv50_msto *msto)
 	struct nv50_mstm *mstm = mstc->mstm;
 	int vcpi = mstc->port->vcpi.vcpi, i;
 
+	WARN_ON(!mutex_is_locked(&mstm->mgr.payload_lock));
+
 	NV_ATOMIC(drm, "%s: vcpi %d\n", msto->encoder.name, vcpi);
 	for (i = 0; i < mstm->mgr.max_payloads; i++) {
 		struct drm_dp_payload *payload = &mstm->mgr.payloads[i];
@@ -733,6 +735,8 @@ nv50_msto_prepare(struct nv50_msto *msto)
 			       (0x0100 << msto->head->base.index),
 	};
 
+	mutex_lock(&mstm->mgr.payload_lock);
+
 	NV_ATOMIC(drm, "%s: msto prepare\n", msto->encoder.name);
 	if (mstc->port->vcpi.vcpi > 0) {
 		struct drm_dp_payload *payload = nv50_msto_payload(msto);
@@ -748,7 +752,9 @@ nv50_msto_prepare(struct nv50_msto *msto)
 		  msto->encoder.name, msto->head->base.base.name,
 		  args.vcpi.start_slot, args.vcpi.num_slots,
 		  args.vcpi.pbn, args.vcpi.aligned_pbn);
+
 	nvif_mthd(&drm->display->disp.object, 0, &args, sizeof(args));
+	mutex_unlock(&mstm->mgr.payload_lock);
 }
 
 static int
-- 
2.20.1

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[PATCH v5 17/20] drm/dp_mst: Add some atomic state iterator macros

[Lyude Paul]

Changes since v6:
 - Move EXPORT_SYMBOL() for drm_dp_mst_topology_state_funcs to this
   commit
 - Document __drm_dp_mst_state_iter_get() and note that it shouldn't be
   called directly

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c |  5 +-
 include/drm/drm_dp_mst_helper.h       | 96 +++++++++++++++++++++++++++
 2 files changed, 99 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index efd8fa29fff6..370371145cdd 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3530,10 +3530,11 @@ static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
 	kfree(mst_state);
 }
 
-static const struct drm_private_state_funcs mst_state_funcs = {
+const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs = {
 	.atomic_duplicate_state = drm_dp_mst_duplicate_state,
 	.atomic_destroy_state = drm_dp_mst_destroy_state,
 };
+EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);
 
 /**
  * drm_atomic_get_mst_topology_state: get MST topology state
@@ -3617,7 +3618,7 @@ int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr,
 
 	drm_atomic_private_obj_init(dev, &mgr->base,
 				    &mst_state->base,
-				    &mst_state_funcs);
+				    &drm_dp_mst_topology_state_funcs);
 
 	return 0;
 }
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 8eca5f29242c..581163c8d7d7 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -650,4 +650,100 @@ int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
 void drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port);
 void drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port);
 
+extern const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs;
+
+/**
+ * __drm_dp_mst_state_iter_get - private atomic state iterator function for
+ * macro-internal use
+ * @state: &struct drm_atomic_state pointer
+ * @mgr: pointer to the &struct drm_dp_mst_topology_mgr iteration cursor
+ * @old_state: optional pointer to the old &struct drm_dp_mst_topology_state
+ * iteration cursor
+ * @new_state: optional pointer to the new &struct drm_dp_mst_topology_state
+ * iteration cursor
+ * @i: int iteration cursor, for macro-internal use
+ *
+ * Used by for_each_oldnew_mst_mgr_in_state(),
+ * for_each_old_mst_mgr_in_state(), and for_each_new_mst_mgr_in_state(). Don't
+ * call this directly.
+ *
+ * Returns:
+ * True if the current &struct drm_private_obj is a &struct
+ * drm_dp_mst_topology_mgr, false otherwise.
+ */
+static inline bool
+__drm_dp_mst_state_iter_get(struct drm_atomic_state *state,
+			    struct drm_dp_mst_topology_mgr **mgr,
+			    struct drm_dp_mst_topology_state **old_state,
+			    struct drm_dp_mst_topology_state **new_state,
+			    int i)
+{
+	struct __drm_private_objs_state *objs_state = &state->private_objs[i];
+
+	if (objs_state->ptr->funcs != &drm_dp_mst_topology_state_funcs)
+		return false;
+
+	*mgr = to_dp_mst_topology_mgr(objs_state->ptr);
+	if (old_state)
+		*old_state = to_dp_mst_topology_state(objs_state->old_state);
+	if (new_state)
+		*new_state = to_dp_mst_topology_state(objs_state->new_state);
+
+	return true;
+}
+
+/**
+ * for_each_oldnew_mst_mgr_in_state - iterate over all DP MST topology
+ * managers in an atomic update
+ * @__state: &struct drm_atomic_state pointer
+ * @mgr: &struct drm_dp_mst_topology_mgr iteration cursor
+ * @old_state: &struct drm_dp_mst_topology_state iteration cursor for the old
+ * state
+ * @new_state: &struct drm_dp_mst_topology_state iteration cursor for the new
+ * state
+ * @__i: int iteration cursor, for macro-internal use
+ *
+ * This iterates over all DRM DP MST topology managers in an atomic update,
+ * tracking both old and new state. This is useful in places where the state
+ * delta needs to be considered, for example in atomic check functions.
+ */
+#define for_each_oldnew_mst_mgr_in_state(__state, mgr, old_state, new_state, __i) \
+	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), &(old_state), &(new_state), (__i)))
+
+/**
+ * for_each_old_mst_mgr_in_state - iterate over all DP MST topology managers
+ * in an atomic update
+ * @__state: &struct drm_atomic_state pointer
+ * @mgr: &struct drm_dp_mst_topology_mgr iteration cursor
+ * @old_state: &struct drm_dp_mst_topology_state iteration cursor for the old
+ * state
+ * @__i: int iteration cursor, for macro-internal use
+ *
+ * This iterates over all DRM DP MST topology managers in an atomic update,
+ * tracking only the old state. This is useful in disable functions, where we
+ * need the old state the hardware is still in.
+ */
+#define for_each_old_mst_mgr_in_state(__state, mgr, old_state, __i) \
+	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), &(old_state), NULL, (__i)))
+
+/**
+ * for_each_new_mst_mgr_in_state - iterate over all DP MST topology managers
+ * in an atomic update
+ * @__state: &struct drm_atomic_state pointer
+ * @mgr: &struct drm_dp_mst_topology_mgr iteration cursor
+ * @new_state: &struct drm_dp_mst_topology_state iteration cursor for the new
+ * state
+ * @__i: int iteration cursor, for macro-internal use
+ *
+ * This iterates over all DRM DP MST topology managers in an atomic update,
+ * tracking only the new state. This is useful in enable functions, where we
+ * need the new state the hardware should be in when the atomic commit
+ * operation has completed.
+ */
+#define for_each_new_mst_mgr_in_state(__state, mgr, new_state, __i) \
+	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), NULL, &(new_state), (__i)))
+
 #endif
-- 
2.20.1

_______________________________________________
amd-gfx mailing list
amd-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/amd-gfx

[PATCH v5 18/20] drm/dp_mst: Start tracking per-port VCPI allocations

[Lyude Paul]

There has been a TODO waiting for quite a long time in
drm_dp_mst_topology.c:

	/* We cannot rely on port->vcpi.num_slots to update
	 * topology_state->avail_slots as the port may not exist if the parent
	 * branch device was unplugged. This should be fixed by tracking
	 * per-port slot allocation in drm_dp_mst_topology_state instead of
	 * depending on the caller to tell us how many slots to release.
	 */

That's not the only reason we should fix this: forcing the driver to
track the VCPI allocations throughout a state's atomic check is
error prone, because it means that extra care has to be taken with the
order that drm_dp_atomic_find_vcpi_slots() and
drm_dp_atomic_release_vcpi_slots() are called in in order to ensure
idempotency. Currently the only driver actually using these helpers,
i915, doesn't even do this correctly: multiple ->best_encoder() checks
with i915's current implementation would not be idempotent and would
over-allocate VCPI slots, something I learned trying to implement
fallback retraining in MST.

So: simplify this whole mess, and teach drm_dp_atomic_find_vcpi_slots()
and drm_dp_atomic_release_vcpi_slots() to track the VCPI allocations for
each port. This allows us to ensure idempotency without having to rely
on the driver as much. Additionally: the driver doesn't need to do any
kind of VCPI slot tracking anymore if it doesn't need it for it's own
internal state.

Additionally; this adds a new drm_dp_mst_atomic_check() helper which
must be used by atomic drivers to perform validity checks for the new
VCPI allocations incurred by a state.

Also: update the documentation and make it more obvious that these
/must/ be called by /all/ atomic drivers supporting MST.

Changes since v9:
* Add some missing changes that were requested by danvet that I forgot
  about after I redid all of the kref stuff:
  * Remove unnecessary state changes in intel_dp_mst_atomic_check
  * Cleanup atomic check logic for VCPI allocations - all we need to check in
    compute_config is whether or not this state disables a CRTC, then free
    VCPI based off that

Changes since v8:
 * Fix compile errors, whoops!

Changes since v7:
 - Don't check for mixed stale/valid VCPI allocations, just rely on
 connector registration to stop such erroneous modesets

Changes since v6:
 - Keep a kref to all of the ports we have allocations on. This required
   a good bit of changing to when we call drm_dp_find_vcpi_slots(),
   mainly that we need to ensure that we only redo VCPI allocations on
   actual mode or CRTC changes, not crtc_state->active changes.
   Additionally, we no longer take the registration of the DRM connector
   for each port into account because so long as we have a kref to the
   port in the new or previous atomic state, the connector will stay
   registered.
 - Use the small changes to drm_dp_put_port() to add even more error
   checking to make misusage of the helpers more obvious. I added this
   after having to chase down various use-after-free conditions that
   started popping up from the new helpers so no one else has to
   troubleshoot that.
 - Move some accidental DRM_DEBUG_KMS() calls to DRM_DEBUG_ATOMIC()
 - Update documentation again, note that find/release() should both not be
   called on the same port in a single atomic check phase (but multiple
   calls to one or the other is OK)

Changes since v4:
 - Don't skip the atomic checks for VCPI allocations if no new VCPI
   allocations happen in a state. This makes the next change I'm about
   to list here a lot easier to implement.
 - Don't ignore VCPI allocations on destroyed ports, instead ensure that
   when ports are destroyed and still have VCPI allocations in the
   topology state, the only state changes allowed are releasing said
   ports' VCPI. This prevents a state with a mix of VCPI allocations
   from destroyed ports, and allocations from valid ports.

Changes since v3:
 - Don't release VCPI allocations in the topology state immediately in
   drm_dp_atomic_release_vcpi_slots(), instead mark them as 0 and skip
   over them in drm_dp_mst_duplicate_state(). This makes it so
   drm_dp_atomic_release_vcpi_slots() is still idempotent while also
   throwing warnings if the driver messes up it's book keeping and tries
   to release VCPI slots on a port that doesn't have any pre-existing
   VCPI allocation - danvet
 - Change mst_state/state in some debugging messages to "mst state"

Changes since v2:
 - Use kmemdup() for duplicating MST state - danvet
 - Move port validation out of duplicate state callback - danvet
 - Handle looping through MST topology states in
   drm_dp_mst_atomic_check() so the driver doesn't have to do it
 - Fix documentation in drm_dp_atomic_find_vcpi_slots()
 - Move the atomic check for each individual topology state into it's
   own function, reduces indenting
 - Don't consider "stale" MST ports when calculating the bandwidth
   requirements. This is needed because originally we relied on the
   state duplication functions to prune any stale ports from the new
   state, which would prevent us from incorrectly considering their
   bandwidth requirements alongside legitimate new payloads.
 - Add function references in drm_dp_atomic_release_vcpi_slots() - danvet
 - Annotate atomic VCPI and atomic check functions with __must_check
   - danvet

Changes since v1:
 - Don't use the now-removed ->atomic_check() for private objects hook,
   just give drivers a function to call themselves

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 247 ++++++++++++++++++++++----
 drivers/gpu/drm/i915/intel_display.c  |   4 +
 drivers/gpu/drm/i915/intel_dp_mst.c   |  54 +++---
 include/drm/drm_dp_mst_helper.h       |  23 ++-
 4 files changed, 266 insertions(+), 62 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 370371145cdd..fc778c6d487e 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3020,21 +3020,42 @@ static int drm_dp_init_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 }
 
 /**
- * drm_dp_atomic_find_vcpi_slots() - Find and add vcpi slots to the state
+ * drm_dp_atomic_find_vcpi_slots() - Find and add VCPI slots to the state
  * @state: global atomic state
  * @mgr: MST topology manager for the port
  * @port: port to find vcpi slots for
  * @pbn: bandwidth required for the mode in PBN
  *
- * RETURNS:
- * Total slots in the atomic state assigned for this port or error
+ * Allocates VCPI slots to @port, replacing any previous VCPI allocations it
+ * may have had. Any atomic drivers which support MST must call this function
+ * in their &drm_encoder_helper_funcs.atomic_check() callback to change the
+ * current VCPI allocation for the new state, but only when
+ * &drm_crtc_state.mode_changed or &drm_crtc_state.connectors_changed is set
+ * to ensure compatibility with userspace applications that still use the
+ * legacy modesetting UAPI.
+ *
+ * Allocations set by this function are not checked against the bandwidth
+ * restraints of @mgr until the driver calls drm_dp_mst_atomic_check().
+ *
+ * Additionally, it is OK to call this function multiple times on the same
+ * @port as needed. It is not OK however, to call this function and
+ * drm_dp_atomic_release_vcpi_slots() in the same atomic check phase.
+ *
+ * See also:
+ * drm_dp_atomic_release_vcpi_slots()
+ * drm_dp_mst_atomic_check()
+ *
+ * Returns:
+ * Total slots in the atomic state assigned for this port, or a negative error
+ * code if the port no longer exists
  */
 int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
 				  struct drm_dp_mst_topology_mgr *mgr,
 				  struct drm_dp_mst_port *port, int pbn)
 {
 	struct drm_dp_mst_topology_state *topology_state;
-	int req_slots;
+	struct drm_dp_vcpi_allocation *pos, *vcpi = NULL;
+	int prev_slots, req_slots, ret;
 
 	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
 	if (IS_ERR(topology_state))
@@ -3043,20 +3064,54 @@ int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
 	port = drm_dp_mst_topology_get_port_validated(mgr, port);
 	if (port == NULL)
 		return -EINVAL;
-	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
-	DRM_DEBUG_KMS("vcpi slots req=%d, avail=%d\n",
-			req_slots, topology_state->avail_slots);
 
-	if (req_slots > topology_state->avail_slots) {
-		drm_dp_mst_topology_put_port(port);
-		return -ENOSPC;
+	/* Find the current allocation for this port, if any */
+	list_for_each_entry(pos, &topology_state->vcpis, next) {
+		if (pos->port == port) {
+			vcpi = pos;
+			prev_slots = vcpi->vcpi;
+
+			/*
+			 * This should never happen, unless the driver tries
+			 * releasing and allocating the same VCPI allocation,
+			 * which is an error
+			 */
+			if (WARN_ON(!prev_slots)) {
+				DRM_ERROR("cannot allocate and release VCPI on [MST PORT:%p] in the same state\n",
+					  port);
+				return -EINVAL;
+			}
+
+			break;
+		}
 	}
+	if (!vcpi)
+		prev_slots = 0;
+
+	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
+
+	DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] [MST PORT:%p] VCPI %d -> %d\n",
+			 port->connector->base.id, port->connector->name,
+			 port, prev_slots, req_slots);
+
+	/* Add the new allocation to the state */
+	if (!vcpi) {
+		vcpi = kzalloc(sizeof(*vcpi), GFP_KERNEL);
+		if (!vcpi) {
+			ret = -ENOMEM;
+			goto out;
+		}
 
-	topology_state->avail_slots -= req_slots;
-	DRM_DEBUG_KMS("vcpi slots avail=%d", topology_state->avail_slots);
+		drm_dp_mst_get_port_malloc(port);
+		vcpi->port = port;
+		list_add(&vcpi->next, &topology_state->vcpis);
+	}
+	vcpi->vcpi = req_slots;
 
+	ret = req_slots;
+out:
 	drm_dp_mst_topology_put_port(port);
-	return req_slots;
+	return ret;
 }
 EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
 
@@ -3064,31 +3119,57 @@ EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
  * drm_dp_atomic_release_vcpi_slots() - Release allocated vcpi slots
  * @state: global atomic state
  * @mgr: MST topology manager for the port
- * @slots: number of vcpi slots to release
+ * @port: The port to release the VCPI slots from
  *
- * RETURNS:
- * 0 if @slots were added back to &drm_dp_mst_topology_state->avail_slots or
- * negative error code
+ * Releases any VCPI slots that have been allocated to a port in the atomic
+ * state. Any atomic drivers which support MST must call this function in
+ * their &drm_connector_helper_funcs.atomic_check() callback when the
+ * connector will no longer have VCPI allocated (e.g. because it's CRTC was
+ * removed) when it had VCPI allocated in the previous atomic state.
+ *
+ * It is OK to call this even if @port has been removed from the system.
+ * Additionally, it is OK to call this function multiple times on the same
+ * @port as needed. It is not OK however, to call this function and
+ * drm_dp_atomic_find_vcpi_slots() on the same @port in a single atomic check
+ * phase.
+ *
+ * See also:
+ * drm_dp_atomic_find_vcpi_slots()
+ * drm_dp_mst_atomic_check()
+ *
+ * Returns:
+ * 0 if all slots for this port were added back to
+ * &drm_dp_mst_topology_state.avail_slots or negative error code
  */
 int drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
 				     struct drm_dp_mst_topology_mgr *mgr,
-				     int slots)
+				     struct drm_dp_mst_port *port)
 {
 	struct drm_dp_mst_topology_state *topology_state;
+	struct drm_dp_vcpi_allocation *pos;
+	bool found = false;
 
 	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
 	if (IS_ERR(topology_state))
 		return PTR_ERR(topology_state);
 
-	/* We cannot rely on port->vcpi.num_slots to update
-	 * topology_state->avail_slots as the port may not exist if the parent
-	 * branch device was unplugged. This should be fixed by tracking
-	 * per-port slot allocation in drm_dp_mst_topology_state instead of
-	 * depending on the caller to tell us how many slots to release.
-	 */
-	topology_state->avail_slots += slots;
-	DRM_DEBUG_KMS("vcpi slots released=%d, avail=%d\n",
-			slots, topology_state->avail_slots);
+	list_for_each_entry(pos, &topology_state->vcpis, next) {
+		if (pos->port == port) {
+			found = true;
+			break;
+		}
+	}
+	if (WARN_ON(!found)) {
+		DRM_ERROR("no VCPI for [MST PORT:%p] found in mst state %p\n",
+			  port, &topology_state->base);
+		return -EINVAL;
+	}
+
+	DRM_DEBUG_ATOMIC("[MST PORT:%p] VCPI %d -> 0\n", port, pos->vcpi);
+	if (pos->vcpi) {
+		drm_dp_mst_put_port_malloc(port);
+		pos->vcpi = 0;
+	}
 
 	return 0;
 }
@@ -3510,15 +3591,41 @@ static void drm_dp_destroy_connector_work(struct work_struct *work)
 static struct drm_private_state *
 drm_dp_mst_duplicate_state(struct drm_private_obj *obj)
 {
-	struct drm_dp_mst_topology_state *state;
+	struct drm_dp_mst_topology_state *state, *old_state =
+		to_dp_mst_topology_state(obj->state);
+	struct drm_dp_vcpi_allocation *pos, *vcpi;
 
-	state = kmemdup(obj->state, sizeof(*state), GFP_KERNEL);
+	state = kmemdup(old_state, sizeof(*state), GFP_KERNEL);
 	if (!state)
 		return NULL;
 
 	__drm_atomic_helper_private_obj_duplicate_state(obj, &state->base);
 
+	INIT_LIST_HEAD(&state->vcpis);
+
+	list_for_each_entry(pos, &old_state->vcpis, next) {
+		/* Prune leftover freed VCPI allocations */
+		if (!pos->vcpi)
+			continue;
+
+		vcpi = kmemdup(pos, sizeof(*vcpi), GFP_KERNEL);
+		if (!vcpi)
+			goto fail;
+
+		drm_dp_mst_get_port_malloc(vcpi->port);
+		list_add(&vcpi->next, &state->vcpis);
+	}
+
 	return &state->base;
+
+fail:
+	list_for_each_entry_safe(pos, vcpi, &state->vcpis, next) {
+		drm_dp_mst_put_port_malloc(pos->port);
+		kfree(pos);
+	}
+	kfree(state);
+
+	return NULL;
 }
 
 static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
@@ -3526,10 +3633,88 @@ static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
 {
 	struct drm_dp_mst_topology_state *mst_state =
 		to_dp_mst_topology_state(state);
+	struct drm_dp_vcpi_allocation *pos, *tmp;
+
+	list_for_each_entry_safe(pos, tmp, &mst_state->vcpis, next) {
+		/* We only keep references to ports with non-zero VCPIs */
+		if (pos->vcpi)
+			drm_dp_mst_put_port_malloc(pos->port);
+		kfree(pos);
+	}
 
 	kfree(mst_state);
 }
 
+static inline int
+drm_dp_mst_atomic_check_topology_state(struct drm_dp_mst_topology_mgr *mgr,
+				       struct drm_dp_mst_topology_state *mst_state)
+{
+	struct drm_dp_vcpi_allocation *vcpi;
+	int avail_slots = 63;
+
+	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
+		/* Releasing VCPI is always OK-even if the port is gone */
+		if (!vcpi->vcpi) {
+			DRM_DEBUG_ATOMIC("[MST PORT:%p] releases all VCPI slots\n",
+					 vcpi->port);
+			continue;
+		}
+
+		DRM_DEBUG_ATOMIC("[MST PORT:%p] requires %d vcpi slots\n",
+				 vcpi->port, vcpi->vcpi);
+
+		avail_slots -= vcpi->vcpi;
+		if (avail_slots < 0) {
+			DRM_DEBUG_ATOMIC("[MST PORT:%p] not enough VCPI slots in mst state %p (avail=%d)\n",
+					 vcpi->port, mst_state,
+					 avail_slots + vcpi->vcpi);
+			return -ENOSPC;
+		}
+	}
+	DRM_DEBUG_ATOMIC("[MST MGR:%p] mst state %p VCPI avail=%d used=%d\n",
+			 mgr, mst_state, avail_slots,
+			 63 - avail_slots);
+
+	return 0;
+}
+
+/**
+ * drm_dp_mst_atomic_check - Check that the new state of an MST topology in an
+ * atomic update is valid
+ * @state: Pointer to the new &struct drm_dp_mst_topology_state
+ *
+ * Checks the given topology state for an atomic update to ensure that it's
+ * valid. This includes checking whether there's enough bandwidth to support
+ * the new VCPI allocations in the atomic update.
+ *
+ * Any atomic drivers supporting DP MST must make sure to call this after
+ * checking the rest of their state in their
+ * &drm_mode_config_funcs.atomic_check() callback.
+ *
+ * See also:
+ * drm_dp_atomic_find_vcpi_slots()
+ * drm_dp_atomic_release_vcpi_slots()
+ *
+ * Returns:
+ *
+ * 0 if the new state is valid, negative error code otherwise.
+ */
+int drm_dp_mst_atomic_check(struct drm_atomic_state *state)
+{
+	struct drm_dp_mst_topology_mgr *mgr;
+	struct drm_dp_mst_topology_state *mst_state;
+	int i, ret = 0;
+
+	for_each_new_mst_mgr_in_state(state, mgr, mst_state, i) {
+		ret = drm_dp_mst_atomic_check_topology_state(mgr, mst_state);
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_dp_mst_atomic_check);
+
 const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs = {
 	.atomic_duplicate_state = drm_dp_mst_duplicate_state,
 	.atomic_destroy_state = drm_dp_mst_destroy_state,
@@ -3612,9 +3797,7 @@ int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr,
 		return -ENOMEM;
 
 	mst_state->mgr = mgr;
-
-	/* max. time slots - one slot for MTP header */
-	mst_state->avail_slots = 63;
+	INIT_LIST_HEAD(&mst_state->vcpis);
 
 	drm_atomic_private_obj_init(dev, &mgr->base,
 				    &mst_state->base,
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 696e6f5680df..d1595be4a880 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12710,6 +12710,10 @@ static int intel_atomic_check(struct drm_device *dev,
 				       "[modeset]" : "[fastset]");
 	}
 
+	ret = drm_dp_mst_atomic_check(state);
+	if (ret)
+		return ret;
+
 	if (any_ms) {
 		ret = intel_modeset_checks(state);
 
diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
index 631fd1537252..c8e2215628e6 100644
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -41,8 +41,12 @@ static bool intel_dp_mst_compute_config(struct intel_encoder *encoder,
 	struct drm_connector *connector = conn_state->connector;
 	void *port = to_intel_connector(connector)->port;
 	struct drm_atomic_state *state = pipe_config->base.state;
+	struct drm_crtc *crtc = pipe_config->base.crtc;
+	struct drm_crtc_state *old_crtc_state =
+		drm_atomic_get_old_crtc_state(state, crtc);
 	int bpp;
-	int lane_count, slots = 0;
+	int lane_count, slots =
+		to_intel_crtc_state(old_crtc_state)->dp_m_n.tu;
 	const struct drm_display_mode *adjusted_mode = &pipe_config->base.adjusted_mode;
 	int mst_pbn;
 	bool constant_n = drm_dp_has_quirk(&intel_dp->desc,
@@ -107,35 +111,39 @@ static bool intel_dp_mst_compute_config(struct intel_encoder *encoder,
 	return true;
 }
 
-static int intel_dp_mst_atomic_check(struct drm_connector *connector,
-		struct drm_connector_state *new_conn_state)
+static int
+intel_dp_mst_atomic_check(struct drm_connector *connector,
+			  struct drm_connector_state *new_conn_state)
 {
 	struct drm_atomic_state *state = new_conn_state->state;
-	struct drm_connector_state *old_conn_state;
-	struct drm_crtc *old_crtc;
+	struct drm_connector_state *old_conn_state =
+		drm_atomic_get_old_connector_state(state, connector);
+	struct intel_connector *intel_connector =
+		to_intel_connector(connector);
+	struct drm_crtc *new_crtc = new_conn_state->crtc;
 	struct drm_crtc_state *crtc_state;
-	int slots, ret = 0;
+	struct drm_dp_mst_topology_mgr *mgr;
+	int ret = 0;
 
-	old_conn_state = drm_atomic_get_old_connector_state(state, connector);
-	old_crtc = old_conn_state->crtc;
-	if (!old_crtc)
-		return ret;
-
-	crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
-	slots = to_intel_crtc_state(crtc_state)->dp_m_n.tu;
-	if (drm_atomic_crtc_needs_modeset(crtc_state) && slots > 0) {
-		struct drm_dp_mst_topology_mgr *mgr;
-		struct drm_encoder *old_encoder;
+	if (!old_conn_state->crtc)
+		return 0;
 
-		old_encoder = old_conn_state->best_encoder;
-		mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
+	/* We only want to free VCPI if this state disables the CRTC on this
+	 * connector
+	 */
+	if (new_crtc) {
+		crtc_state = drm_atomic_get_new_crtc_state(state, new_crtc);
 
-		ret = drm_dp_atomic_release_vcpi_slots(state, mgr, slots);
-		if (ret)
-			DRM_DEBUG_KMS("failed releasing %d vcpi slots:%d\n", slots, ret);
-		else
-			to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
+		if (!crtc_state ||
+		    !drm_atomic_crtc_needs_modeset(crtc_state) ||
+		    crtc_state->enable)
+			return 0;
 	}
+
+	mgr = &enc_to_mst(old_conn_state->best_encoder)->primary->dp.mst_mgr;
+	ret = drm_dp_atomic_release_vcpi_slots(state, mgr,
+					       intel_connector->port);
+
 	return ret;
 }
 
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 581163c8d7d7..451d020f0137 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -425,9 +425,15 @@ struct drm_dp_payload {
 
 #define to_dp_mst_topology_state(x) container_of(x, struct drm_dp_mst_topology_state, base)
 
+struct drm_dp_vcpi_allocation {
+	struct drm_dp_mst_port *port;
+	int vcpi;
+	struct list_head next;
+};
+
 struct drm_dp_mst_topology_state {
 	struct drm_private_state base;
-	int avail_slots;
+	struct list_head vcpis;
 	struct drm_dp_mst_topology_mgr *mgr;
 };
 
@@ -638,14 +644,17 @@ void drm_dp_mst_topology_mgr_suspend(struct drm_dp_mst_topology_mgr *mgr);
 int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr);
 struct drm_dp_mst_topology_state *drm_atomic_get_mst_topology_state(struct drm_atomic_state *state,
 								    struct drm_dp_mst_topology_mgr *mgr);
-int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
-				  struct drm_dp_mst_topology_mgr *mgr,
-				  struct drm_dp_mst_port *port, int pbn);
-int drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
-				     struct drm_dp_mst_topology_mgr *mgr,
-				     int slots);
+int __must_check
+drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
+			      struct drm_dp_mst_topology_mgr *mgr,
+			      struct drm_dp_mst_port *port, int pbn);
+int __must_check
+drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
+				 struct drm_dp_mst_topology_mgr *mgr,
+				 struct drm_dp_mst_port *port);
 int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
 				 struct drm_dp_mst_port *port, bool power_up);
+int __must_check drm_dp_mst_atomic_check(struct drm_atomic_state *state);
 
 void drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port);
 void drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port);
-- 
2.20.1

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[PATCH v5 19/20] drm/dp_mst: Check payload count in drm_dp_mst_atomic_check()

[Lyude Paul]

It occurred to me that we never actually check this! So let's start
doing that.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index fc778c6d487e..41cf814207bf 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3650,7 +3650,7 @@ drm_dp_mst_atomic_check_topology_state(struct drm_dp_mst_topology_mgr *mgr,
 				       struct drm_dp_mst_topology_state *mst_state)
 {
 	struct drm_dp_vcpi_allocation *vcpi;
-	int avail_slots = 63;
+	int avail_slots = 63, payload_count = 0;
 
 	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
 		/* Releasing VCPI is always OK-even if the port is gone */
@@ -3670,6 +3670,12 @@ drm_dp_mst_atomic_check_topology_state(struct drm_dp_mst_topology_mgr *mgr,
 					 avail_slots + vcpi->vcpi);
 			return -ENOSPC;
 		}
+
+		if (++payload_count > mgr->max_payloads) {
+			DRM_DEBUG_ATOMIC("[MST MGR:%p] state %p has too many payloads (max=%d)\n",
+					 mgr, mst_state, mgr->max_payloads);
+			return -EINVAL;
+		}
 	}
 	DRM_DEBUG_ATOMIC("[MST MGR:%p] mst state %p VCPI avail=%d used=%d\n",
 			 mgr, mst_state, avail_slots,
-- 
2.20.1

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[PATCH v5 20/20] drm/nouveau: Use atomic VCPI helpers for MST

[Lyude Paul]

Currently, nouveau uses the yolo method of setting up MST displays: it
uses the old VCPI helpers (drm_dp_find_vcpi_slots()) for computing the
display configuration. These helpers don't take care to make sure they
take a reference to the mstb port that they're checking, and
additionally don't actually check whether or not the topology still has
enough bandwidth to provide the VCPI tokens required.

So, drop usage of the old helpers and move entirely over to the atomic
helpers.

Changes since v6:
* Cleanup atomic check logic and remove a bunch of unneeded checks -
  danvet
Changes since v5:
* Update nv50_msto_atomic_check() and nv50_mstc_atomic_check() to the
  new requirements for drm_dp_atomic_find_vcpi_slots() and
  drm_dp_atomic_release_vcpi_slots()

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Airlie <airlied@redhat.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Juston Li <juston.li@intel.com>
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c | 54 ++++++++++++++++++++++---
 1 file changed, 48 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 67f7bf97e5d9..53d6c8df8f68 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -762,16 +762,23 @@ nv50_msto_atomic_check(struct drm_encoder *encoder,
 		       struct drm_crtc_state *crtc_state,
 		       struct drm_connector_state *conn_state)
 {
-	struct nv50_mstc *mstc = nv50_mstc(conn_state->connector);
+	struct drm_atomic_state *state = crtc_state->state;
+	struct drm_connector *connector = conn_state->connector;
+	struct nv50_mstc *mstc = nv50_mstc(connector);
 	struct nv50_mstm *mstm = mstc->mstm;
-	int bpp = conn_state->connector->display_info.bpc * 3;
+	int bpp = connector->display_info.bpc * 3;
 	int slots;
 
-	mstc->pbn = drm_dp_calc_pbn_mode(crtc_state->adjusted_mode.clock, bpp);
+	mstc->pbn = drm_dp_calc_pbn_mode(crtc_state->adjusted_mode.clock,
+					 bpp);
 
-	slots = drm_dp_find_vcpi_slots(&mstm->mgr, mstc->pbn);
-	if (slots < 0)
-		return slots;
+	if (drm_atomic_crtc_needs_modeset(crtc_state) &&
+	    !drm_connector_is_unregistered(connector)) {
+		slots = drm_dp_atomic_find_vcpi_slots(state, &mstm->mgr,
+						      mstc->port, mstc->pbn);
+		if (slots < 0)
+			return slots;
+	}
 
 	return nv50_outp_atomic_check_view(encoder, crtc_state, conn_state,
 					   mstc->native);
@@ -934,12 +941,43 @@ nv50_mstc_get_modes(struct drm_connector *connector)
 	return ret;
 }
 
+static int
+nv50_mstc_atomic_check(struct drm_connector *connector,
+		       struct drm_connector_state *new_conn_state)
+{
+	struct drm_atomic_state *state = new_conn_state->state;
+	struct nv50_mstc *mstc = nv50_mstc(connector);
+	struct drm_dp_mst_topology_mgr *mgr = &mstc->mstm->mgr;
+	struct drm_connector_state *old_conn_state =
+		drm_atomic_get_old_connector_state(state, connector);
+	struct drm_crtc_state *crtc_state;
+	struct drm_crtc *new_crtc = new_conn_state->crtc;
+
+	if (!old_conn_state->crtc)
+		return 0;
+
+	/* We only want to free VCPI if this state disables the CRTC on this
+	 * connector
+	 */
+	if (new_crtc) {
+		crtc_state = drm_atomic_get_new_crtc_state(state, new_crtc);
+
+		if (!crtc_state ||
+		    !drm_atomic_crtc_needs_modeset(crtc_state) ||
+		    crtc_state->enable)
+			return 0;
+	}
+
+	return drm_dp_atomic_release_vcpi_slots(state, mgr, mstc->port);
+}
+
 static const struct drm_connector_helper_funcs
 nv50_mstc_help = {
 	.get_modes = nv50_mstc_get_modes,
 	.mode_valid = nv50_mstc_mode_valid,
 	.best_encoder = nv50_mstc_best_encoder,
 	.atomic_best_encoder = nv50_mstc_atomic_best_encoder,
+	.atomic_check = nv50_mstc_atomic_check,
 };
 
 static enum drm_connector_status
@@ -2121,6 +2159,10 @@ nv50_disp_atomic_check(struct drm_device *dev, struct drm_atomic_state *state)
 			return ret;
 	}
 
+	ret = drm_dp_mst_atomic_check(state);
+	if (ret)
+		return ret;
+
 	return 0;
 }
 
-- 
2.20.1

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✗ Fi.CI.CHECKPATCH: warning for MST refcounting/atomic helpers cleanup (rev5)

[Patchwork]

== Series Details ==

Series: MST refcounting/atomic helpers cleanup (rev5)
URL   : https://patchwork.freedesktop.org/series/54030/
State : warning

== Summary ==

$ dim checkpatch origin/drm-tip
5778d100cac7 drm/dp_mst: Fix some formatting in drm_dp_add_port()
2fd355b3a9aa drm/dp_mst: Fix some formatting in drm_dp_payload_send_msg()
f7a476bd0e0f drm/dp_mst: Fix some formatting in drm_dp_mst_allocate_vcpi()
0b7daea7eab8 drm/dp_mst: Fix some formatting in drm_dp_mst_deallocate_vcpi()
bc368b90cb12 drm/dp_mst: Rename drm_dp_mst_get_validated_(port|mstb)_ref and friends
-:84: CHECK:OPEN_ENDED_LINE: Lines should not end with a '('
#84: FILE: drivers/gpu/drm/drm_dp_mst_topology.c:990:
+			rmstb = drm_dp_mst_topology_get_mstb_validated_locked(

-:102: CHECK:OPEN_ENDED_LINE: Lines should not end with a '('
#102: FILE: drivers/gpu/drm/drm_dp_mst_topology.c:1006:
+		rmstb = drm_dp_mst_topology_get_mstb_validated_locked(

-:150: CHECK:OPEN_ENDED_LINE: Lines should not end with a '('
#150: FILE: drivers/gpu/drm/drm_dp_mst_topology.c:1379:
+			mstb_child = drm_dp_mst_topology_get_mstb_validated(

total: 0 errors, 0 warnings, 3 checks, 401 lines checked
f212460470bf drm/dp_mst: Introduce new refcounting scheme for mstbs and ports
-:27: WARNING:COMMIT_LOG_LONG_LINE: Possible unwrapped commit description (prefer a maximum 75 chars per line)
#27: 
commit 263efde31f97 ("drm/dp/mst: Get validated port ref in drm_dp_update_payload_part1()")

-:51: ERROR:GIT_COMMIT_ID: Please use git commit description style 'commit <12+ chars of sha1> ("<title line>")' - ie: 'commit 9765635b3075 ("Revert "drm/dp_mst: Skip validating ports during destruction, just ref"")'
#51: 
commit 9765635b3075 ("Revert "drm/dp_mst: Skip validating ports during destruction, just ref"")

-:137: WARNING:FILE_PATH_CHANGES: added, moved or deleted file(s), does MAINTAINERS need updating?
#137: 
new file mode 100644

-:842: CHECK:OPEN_ENDED_LINE: Lines should not end with a '('
#842: FILE: drivers/gpu/drm/drm_dp_mst_topology.c:1329:
+			mport = drm_dp_mst_topology_get_port_validated_locked(

-:856: CHECK:OPEN_ENDED_LINE: Lines should not end with a '('
#856: FILE: drivers/gpu/drm/drm_dp_mst_topology.c:1346:
+		rport = drm_dp_mst_topology_get_port_validated_locked(

total: 1 errors, 2 warnings, 2 checks, 915 lines checked
a1f9438797bb drm/dp_mst: Restart last_connected_port_and_mstb() if topology ref fails
11a9df239381 drm/dp_mst: Stop releasing VCPI when removing ports from topology
33e82d971527 drm/dp_mst: Fix payload deallocation on hotplugs using malloc refs
-:97: CHECK:OPEN_ENDED_LINE: Lines should not end with a '('
#97: FILE: drivers/gpu/drm/drm_dp_mst_topology.c:2278:
+				port = drm_dp_mst_topology_get_port_validated(

total: 0 errors, 0 warnings, 1 checks, 124 lines checked
89d20c7c627b drm/i915: Keep malloc references to MST ports
f0300e01a8cf drm/amdgpu/display: Keep malloc ref to MST port
523545b36c93 drm/nouveau: Remove bogus cleanup in nv50_mstm_add_connector()
171456c757e5 drm/nouveau: Remove unnecessary VCPI checks in nv50_msto_cleanup()
a7f4c8e68b5d drm/nouveau: Keep malloc references to MST ports
916a684cd19b drm/nouveau: Stop unsetting mstc->port, use malloc refs
01a9632ebf65 drm/nouveau: Grab payload lock in nv50_msto_payload()
d1f83b76bee9 drm/dp_mst: Add some atomic state iterator macros
-:110: CHECK:MACRO_ARG_REUSE: Macro argument reuse '__state' - possible side-effects?
#110: FILE: include/drm/drm_dp_mst_helper.h:711:
+#define for_each_oldnew_mst_mgr_in_state(__state, mgr, old_state, new_state, __i) \
+	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), &(old_state), &(new_state), (__i)))

-:110: CHECK:MACRO_ARG_REUSE: Macro argument reuse '__i' - possible side-effects?
#110: FILE: include/drm/drm_dp_mst_helper.h:711:
+#define for_each_oldnew_mst_mgr_in_state(__state, mgr, old_state, new_state, __i) \
+	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), &(old_state), &(new_state), (__i)))

-:112: WARNING:LONG_LINE: line over 100 characters
#112: FILE: include/drm/drm_dp_mst_helper.h:713:
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), &(old_state), &(new_state), (__i)))

-:127: CHECK:MACRO_ARG_REUSE: Macro argument reuse '__state' - possible side-effects?
#127: FILE: include/drm/drm_dp_mst_helper.h:728:
+#define for_each_old_mst_mgr_in_state(__state, mgr, old_state, __i) \
+	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), &(old_state), NULL, (__i)))

-:127: CHECK:MACRO_ARG_REUSE: Macro argument reuse '__i' - possible side-effects?
#127: FILE: include/drm/drm_dp_mst_helper.h:728:
+#define for_each_old_mst_mgr_in_state(__state, mgr, old_state, __i) \
+	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), &(old_state), NULL, (__i)))

-:129: WARNING:LONG_LINE: line over 100 characters
#129: FILE: include/drm/drm_dp_mst_helper.h:730:
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), &(old_state), NULL, (__i)))

-:145: CHECK:MACRO_ARG_REUSE: Macro argument reuse '__state' - possible side-effects?
#145: FILE: include/drm/drm_dp_mst_helper.h:746:
+#define for_each_new_mst_mgr_in_state(__state, mgr, new_state, __i) \
+	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), NULL, &(new_state), (__i)))

-:145: CHECK:MACRO_ARG_REUSE: Macro argument reuse '__i' - possible side-effects?
#145: FILE: include/drm/drm_dp_mst_helper.h:746:
+#define for_each_new_mst_mgr_in_state(__state, mgr, new_state, __i) \
+	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), NULL, &(new_state), (__i)))

-:147: WARNING:LONG_LINE: line over 100 characters
#147: FILE: include/drm/drm_dp_mst_helper.h:748:
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), NULL, &(new_state), (__i)))

total: 0 errors, 3 warnings, 6 checks, 120 lines checked
9077cacf44e8 drm/dp_mst: Start tracking per-port VCPI allocations
-:45: WARNING:COMMIT_LOG_LONG_LINE: Possible unwrapped commit description (prefer a maximum 75 chars per line)
#45: 
  * Cleanup atomic check logic for VCPI allocations - all we need to check in

total: 0 errors, 1 warnings, 0 checks, 444 lines checked
1acb8253f5b7 drm/dp_mst: Check payload count in drm_dp_mst_atomic_check()
d6b0067e30e5 drm/nouveau: Use atomic VCPI helpers for MST

_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

✓ Fi.CI.BAT: success for MST refcounting/atomic helpers cleanup (rev5)

[Patchwork]

== Series Details ==

Series: MST refcounting/atomic helpers cleanup (rev5)
URL   : https://patchwork.freedesktop.org/series/54030/
State : success

== Summary ==

CI Bug Log - changes from CI_DRM_5380 -> Patchwork_11258
====================================================

Summary
-------

  **WARNING**

  Minor unknown changes coming with Patchwork_11258 need to be verified
  manually.
  
  If you think the reported changes have nothing to do with the changes
  introduced in Patchwork_11258, please notify your bug team to allow them
  to document this new failure mode, which will reduce false positives in CI.

  External URL: https://patchwork.freedesktop.org/api/1.0/series/54030/revisions/5/

Possible new issues
-------------------

  Here are the unknown changes that may have been introduced in Patchwork_11258:

### IGT changes ###

#### Warnings ####

  * igt@kms_flip@basic-flip-vs-dpms:
    - fi-skl-6770hq:      SKIP -> PASS +36

  
Known issues
------------

  Here are the changes found in Patchwork_11258 that come from known issues:

### IGT changes ###

#### Issues hit ####

  * igt@amdgpu/amd_basic@userptr:
    - fi-kbl-8809g:       PASS -> DMESG-WARN [fdo#108965]

  * igt@i915_selftest@live_hangcheck:
    - fi-skl-guc:         PASS -> DMESG-FAIL [fdo#108593]

  * igt@kms_chamelium@hdmi-hpd-fast:
    - fi-kbl-7500u:       PASS -> FAIL [fdo#108767]

  * igt@kms_pipe_crc_basic@read-crc-pipe-b:
    - fi-byt-clapper:     PASS -> FAIL [fdo#107362]

  * igt@pm_rpm@module-reload:
    - fi-icl-u2:          PASS -> DMESG-WARN [fdo#108654]

  
#### Possible fixes ####

  * igt@kms_pipe_crc_basic@nonblocking-crc-pipe-a-frame-sequence:
    - fi-byt-clapper:     FAIL [fdo#103191] / [fdo#107362] -> PASS

  
  {name}: This element is suppressed. This means it is ignored when computing
          the status of the difference (SUCCESS, WARNING, or FAILURE).

  [fdo#103191]: https://bugs.freedesktop.org/show_bug.cgi?id=103191
  [fdo#107362]: https://bugs.freedesktop.org/show_bug.cgi?id=107362
  [fdo#108593]: https://bugs.freedesktop.org/show_bug.cgi?id=108593
  [fdo#108654]: https://bugs.freedesktop.org/show_bug.cgi?id=108654
  [fdo#108767]: https://bugs.freedesktop.org/show_bug.cgi?id=108767
  [fdo#108965]: https://bugs.freedesktop.org/show_bug.cgi?id=108965
  [fdo#109241]: https://bugs.freedesktop.org/show_bug.cgi?id=109241


Participating hosts (49 -> 44)
------------------------------

  Missing    (5): fi-ilk-m540 fi-byt-squawks fi-bsw-cyan fi-icl-y fi-bdw-samus 


Build changes
-------------

    * Linux: CI_DRM_5380 -> Patchwork_11258

  CI_DRM_5380: f7836843c875734c42d61d755d822635390ab097 @ git://anongit.freedesktop.org/gfx-ci/linux
  IGT_4757: 738f43a54d626f08e250c926a5aeec53458fbd3c @ git://anongit.freedesktop.org/xorg/app/intel-gpu-tools
  Patchwork_11258: d6b0067e30e569204fbf1adab5df2e552713fefc @ git://anongit.freedesktop.org/gfx-ci/linux


== Linux commits ==

d6b0067e30e5 drm/nouveau: Use atomic VCPI helpers for MST
1acb8253f5b7 drm/dp_mst: Check payload count in drm_dp_mst_atomic_check()
9077cacf44e8 drm/dp_mst: Start tracking per-port VCPI allocations
d1f83b76bee9 drm/dp_mst: Add some atomic state iterator macros
01a9632ebf65 drm/nouveau: Grab payload lock in nv50_msto_payload()
916a684cd19b drm/nouveau: Stop unsetting mstc->port, use malloc refs
a7f4c8e68b5d drm/nouveau: Keep malloc references to MST ports
171456c757e5 drm/nouveau: Remove unnecessary VCPI checks in nv50_msto_cleanup()
523545b36c93 drm/nouveau: Remove bogus cleanup in nv50_mstm_add_connector()
f0300e01a8cf drm/amdgpu/display: Keep malloc ref to MST port
89d20c7c627b drm/i915: Keep malloc references to MST ports
33e82d971527 drm/dp_mst: Fix payload deallocation on hotplugs using malloc refs
11a9df239381 drm/dp_mst: Stop releasing VCPI when removing ports from topology
a1f9438797bb drm/dp_mst: Restart last_connected_port_and_mstb() if topology ref fails
f212460470bf drm/dp_mst: Introduce new refcounting scheme for mstbs and ports
bc368b90cb12 drm/dp_mst: Rename drm_dp_mst_get_validated_(port|mstb)_ref and friends
0b7daea7eab8 drm/dp_mst: Fix some formatting in drm_dp_mst_deallocate_vcpi()
f7a476bd0e0f drm/dp_mst: Fix some formatting in drm_dp_mst_allocate_vcpi()
2fd355b3a9aa drm/dp_mst: Fix some formatting in drm_dp_payload_send_msg()
5778d100cac7 drm/dp_mst: Fix some formatting in drm_dp_add_port()

== Logs ==

For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_11258/
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

✓ Fi.CI.IGT: success for MST refcounting/atomic helpers cleanup (rev5)

[Patchwork]

== Series Details ==

Series: MST refcounting/atomic helpers cleanup (rev5)
URL   : https://patchwork.freedesktop.org/series/54030/
State : success

== Summary ==

CI Bug Log - changes from CI_DRM_5380_full -> Patchwork_11258_full
====================================================

Summary
-------

  **SUCCESS**

  No regressions found.

  

Known issues
------------

  Here are the changes found in Patchwork_11258_full that come from known issues:

### IGT changes ###

#### Issues hit ####

  * igt@gem_exec_schedule@pi-ringfull-blt:
    - shard-iclb:         NOTRUN -> FAIL [fdo#103158]

  * igt@gem_exec_schedule@pi-ringfull-bsd:
    - shard-skl:          NOTRUN -> FAIL [fdo#103158] +1

  * igt@gem_ppgtt@blt-vs-render-ctx0:
    - shard-skl:          PASS -> TIMEOUT [fdo#108039]

  * igt@kms_busy@extended-modeset-hang-newfb-render-a:
    - shard-skl:          NOTRUN -> DMESG-WARN [fdo#107956] +2

  * igt@kms_busy@extended-modeset-hang-newfb-with-reset-render-a:
    - shard-iclb:         NOTRUN -> DMESG-WARN [fdo#107956]

  * igt@kms_ccs@pipe-a-crc-primary-basic:
    - shard-iclb:         NOTRUN -> FAIL [fdo#107725]

  * igt@kms_ccs@pipe-a-crc-sprite-planes-basic:
    - shard-apl:          PASS -> FAIL [fdo#106510] / [fdo#108145]

  * igt@kms_color@pipe-a-ctm-max:
    - shard-skl:          NOTRUN -> FAIL [fdo#108147]

  * igt@kms_color@pipe-a-gamma:
    - shard-skl:          NOTRUN -> FAIL [fdo#104782]

  * igt@kms_color@pipe-a-legacy-gamma:
    - shard-apl:          PASS -> FAIL [fdo#104782] / [fdo#108145]

  * igt@kms_color@pipe-c-legacy-gamma:
    - shard-apl:          PASS -> FAIL [fdo#104782]

  * igt@kms_cursor_crc@cursor-128x42-random:
    - shard-skl:          NOTRUN -> FAIL [fdo#103232]

  * igt@kms_cursor_crc@cursor-64x21-random:
    - shard-apl:          PASS -> FAIL [fdo#103232] +1

  * igt@kms_cursor_crc@cursor-64x64-suspend:
    - shard-apl:          PASS -> FAIL [fdo#103191] / [fdo#103232]

  * igt@kms_draw_crc@draw-method-rgb565-blt-xtiled:
    - shard-skl:          PASS -> FAIL [fdo#103184]

  * igt@kms_draw_crc@draw-method-xrgb8888-pwrite-untiled:
    - shard-skl:          PASS -> FAIL [fdo#108472]

  * igt@kms_fbcon_fbt@psr-suspend:
    - shard-skl:          NOTRUN -> FAIL [fdo#107882]

  * igt@kms_flip@flip-vs-expired-vblank-interruptible:
    - shard-skl:          PASS -> FAIL [fdo#105363]

  * igt@kms_frontbuffer_tracking@fbcpsr-1p-primscrn-pri-shrfb-draw-mmap-gtt:
    - shard-skl:          NOTRUN -> FAIL [fdo#105682]

  * igt@kms_frontbuffer_tracking@fbcpsr-1p-primscrn-spr-indfb-onoff:
    - shard-iclb:         PASS -> FAIL [fdo#103167] +1

  * igt@kms_frontbuffer_tracking@fbcpsr-farfromfence:
    - shard-skl:          NOTRUN -> FAIL [fdo#103167] +6

  * igt@kms_frontbuffer_tracking@fbcpsr-suspend:
    - shard-skl:          PASS -> INCOMPLETE [fdo#104108] / [fdo#106978] / [fdo#107773]

  * igt@kms_frontbuffer_tracking@psr-1p-primscrn-shrfb-pgflip-blt:
    - shard-skl:          PASS -> FAIL [fdo#103167] +1

  * igt@kms_pipe_crc_basic@suspend-read-crc-pipe-a:
    - shard-skl:          PASS -> INCOMPLETE [fdo#104108] / [fdo#107773]

  * igt@kms_plane@pixel-format-pipe-b-planes-source-clamping:
    - shard-skl:          NOTRUN -> DMESG-WARN [fdo#106885] +1

  * igt@kms_plane_alpha_blend@pipe-a-alpha-7efc:
    - shard-skl:          NOTRUN -> FAIL [fdo#107815] / [fdo#108145] +2

  * igt@kms_plane_alpha_blend@pipe-a-coverage-7efc:
    - shard-skl:          PASS -> FAIL [fdo#107815] / [fdo#108145]

  * igt@kms_plane_alpha_blend@pipe-b-alpha-7efc:
    - shard-kbl:          NOTRUN -> FAIL [fdo#108145] / [fdo#108590]

  * igt@kms_plane_alpha_blend@pipe-b-constant-alpha-max:
    - shard-apl:          PASS -> FAIL [fdo#108145]

  * igt@kms_plane_multiple@atomic-pipe-b-tiling-yf:
    - shard-iclb:         PASS -> FAIL [fdo#103166] +3

  * igt@kms_psr@no_drrs:
    - shard-iclb:         PASS -> FAIL [fdo#108341]

  * igt@kms_rotation_crc@multiplane-rotation-cropping-top:
    - shard-apl:          PASS -> DMESG-FAIL [fdo#108950]

  * igt@pm_rpm@gem-mmap-gtt:
    - shard-kbl:          PASS -> DMESG-WARN [fdo#103558] / [fdo#105602] +8

  * igt@syncobj_basic@bad-pad-fd-to-handle:
    - shard-apl:          PASS -> INCOMPLETE [fdo#103927]

  
#### Possible fixes ####

  * igt@gem_exec_whisper@normal:
    - shard-skl:          TIMEOUT [fdo#108592] -> PASS

  * igt@gem_workarounds@suspend-resume-fd:
    - shard-skl:          INCOMPLETE [fdo#104108] / [fdo#107773] -> PASS +1

  * igt@kms_busy@extended-modeset-hang-newfb-with-reset-render-b:
    - shard-iclb:         DMESG-WARN [fdo#107956] -> PASS

  * igt@kms_cursor_crc@cursor-128x128-random:
    - shard-kbl:          DMESG-WARN [fdo#103313] -> PASS

  * igt@kms_cursor_crc@cursor-64x64-random:
    - shard-apl:          FAIL [fdo#103232] -> PASS

  * igt@kms_cursor_legacy@cursor-vs-flip-atomic-transitions-varying-size:
    - shard-iclb:         FAIL [fdo#103355] -> PASS

  * igt@kms_frontbuffer_tracking@fbc-1p-primscrn-spr-indfb-draw-pwrite:
    - shard-iclb:         FAIL [fdo#103167] -> PASS +2

  * igt@kms_plane_multiple@atomic-pipe-a-tiling-y:
    - shard-iclb:         FAIL [fdo#103166] -> PASS +2

  * igt@kms_setmode@basic:
    - shard-apl:          FAIL [fdo#99912] -> PASS
    - shard-kbl:          FAIL [fdo#99912] -> PASS

  * igt@kms_vblank@pipe-c-wait-forked:
    - shard-kbl:          DMESG-WARN [fdo#103313] / [fdo#105345] -> PASS

  * igt@pm_rpm@fences-dpms:
    - shard-iclb:         DMESG-WARN [fdo#108654] -> PASS +1

  * igt@pm_rpm@modeset-stress-extra-wait:
    - shard-skl:          INCOMPLETE [fdo#107807] -> PASS

  
#### Warnings ####

  * igt@kms_cursor_crc@cursor-128x128-suspend:
    - shard-iclb:         INCOMPLETE [fdo#107713] -> FAIL [fdo#103232]

  * igt@kms_rotation_crc@multiplane-rotation-cropping-top:
    - shard-kbl:          DMESG-FAIL [fdo#108950] -> DMESG-WARN [fdo#105604]

  
  {name}: This element is suppressed. This means it is ignored when computing
          the status of the difference (SUCCESS, WARNING, or FAILURE).

  [fdo#103158]: https://bugs.freedesktop.org/show_bug.cgi?id=103158
  [fdo#103166]: https://bugs.freedesktop.org/show_bug.cgi?id=103166
  [fdo#103167]: https://bugs.freedesktop.org/show_bug.cgi?id=103167
  [fdo#103184]: https://bugs.freedesktop.org/show_bug.cgi?id=103184
  [fdo#103191]: https://bugs.freedesktop.org/show_bug.cgi?id=103191
  [fdo#103232]: https://bugs.freedesktop.org/show_bug.cgi?id=103232
  [fdo#103313]: https://bugs.freedesktop.org/show_bug.cgi?id=103313
  [fdo#103355]: https://bugs.freedesktop.org/show_bug.cgi?id=103355
  [fdo#103558]: https://bugs.freedesktop.org/show_bug.cgi?id=103558
  [fdo#103927]: https://bugs.freedesktop.org/show_bug.cgi?id=103927
  [fdo#104108]: https://bugs.freedesktop.org/show_bug.cgi?id=104108
  [fdo#104782]: https://bugs.freedesktop.org/show_bug.cgi?id=104782
  [fdo#105345]: https://bugs.freedesktop.org/show_bug.cgi?id=105345
  [fdo#105363]: https://bugs.freedesktop.org/show_bug.cgi?id=105363
  [fdo#105602]: https://bugs.freedesktop.org/show_bug.cgi?id=105602
  [fdo#105604]: https://bugs.freedesktop.org/show_bug.cgi?id=105604
  [fdo#105682]: https://bugs.freedesktop.org/show_bug.cgi?id=105682
  [fdo#106510]: https://bugs.freedesktop.org/show_bug.cgi?id=106510
  [fdo#106885]: https://bugs.freedesktop.org/show_bug.cgi?id=106885
  [fdo#106978]: https://bugs.freedesktop.org/show_bug.cgi?id=106978
  [fdo#107469]: https://bugs.freedesktop.org/show_bug.cgi?id=107469
  [fdo#107713]: https://bugs.freedesktop.org/show_bug.cgi?id=107713
  [fdo#107725]: https://bugs.freedesktop.org/show_bug.cgi?id=107725
  [fdo#107773]: https://bugs.freedesktop.org/show_bug.cgi?id=107773
  [fdo#107807]: https://bugs.freedesktop.org/show_bug.cgi?id=107807
  [fdo#107815]: https://bugs.freedesktop.org/show_bug.cgi?id=107815
  [fdo#107882]: https://bugs.freedesktop.org/show_bug.cgi?id=107882
  [fdo#107956]: https://bugs.freedesktop.org/show_bug.cgi?id=107956
  [fdo#108039]: https://bugs.freedesktop.org/show_bug.cgi?id=108039
  [fdo#108145]: https://bugs.freedesktop.org/show_bug.cgi?id=108145
  [fdo#108147]: https://bugs.freedesktop.org/show_bug.cgi?id=108147
  [fdo#108341]: https://bugs.freedesktop.org/show_bug.cgi?id=108341
  [fdo#108472]: https://bugs.freedesktop.org/show_bug.cgi?id=108472
  [fdo#108590]: https://bugs.freedesktop.org/show_bug.cgi?id=108590
  [fdo#108592]: https://bugs.freedesktop.org/show_bug.cgi?id=108592
  [fdo#108654]: https://bugs.freedesktop.org/show_bug.cgi?id=108654
  [fdo#108784]: https://bugs.freedesktop.org/show_bug.cgi?id=108784
  [fdo#108950]: https://bugs.freedesktop.org/show_bug.cgi?id=108950
  [fdo#109241]: https://bugs.freedesktop.org/show_bug.cgi?id=109241
  [fdo#99912]: https://bugs.freedesktop.org/show_bug.cgi?id=99912


Participating hosts (6 -> 6)
------------------------------

  No changes in participating hosts


Build changes
-------------

    * Linux: CI_DRM_5380 -> Patchwork_11258

  CI_DRM_5380: f7836843c875734c42d61d755d822635390ab097 @ git://anongit.freedesktop.org/gfx-ci/linux
  IGT_4757: 738f43a54d626f08e250c926a5aeec53458fbd3c @ git://anongit.freedesktop.org/xorg/app/intel-gpu-tools
  Patchwork_11258: d6b0067e30e569204fbf1adab5df2e552713fefc @ git://anongit.freedesktop.org/gfx-ci/linux
  piglit_4509: fdc5a4ca11124ab8413c7988896eec4c97336694 @ git://anongit.freedesktop.org/piglit

== Logs ==

For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_11258/
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

Re: [PATCH v5 06/20] drm/dp_mst: Introduce new refcounting scheme for mstbs and ports

[Daniel Vetter]

On Tue, Jan 08, 2019 at 07:35:03PM -0500, Lyude Paul wrote:
> The current way of handling refcounting in the DP MST helpers is really
> confusing and probably just plain wrong because it's been hacked up many
> times over the years without anyone actually going over the code and
> seeing if things could be simplified.
> 
> To the best of my understanding, the current scheme works like this:
> drm_dp_mst_port and drm_dp_mst_branch both have a single refcount. When
> this refcount hits 0 for either of the two, they're removed from the
> topology state, but not immediately freed. Both ports and branch devices
> will reinitialize their kref once it's hit 0 before actually destroying
> themselves. The intended purpose behind this is so that we can avoid
> problems like not being able to free a remote payload that might still
> be active, due to us having removed all of the port/branch device
> structures in memory, as per:
> 
> commit 91a25e463130 ("drm/dp/mst: deallocate payload on port destruction")
> 
> Which may have worked, but then it caused use-after-free errors. Being
> new to MST at the time, I tried fixing it;
> 
> commit 263efde31f97 ("drm/dp/mst: Get validated port ref in drm_dp_update_payload_part1()")
> 
> But, that was broken: both drm_dp_mst_port and drm_dp_mst_branch structs
> are validated in almost every DP MST helper function. Simply put, this
> means we go through the topology and try to see if the given
> drm_dp_mst_branch or drm_dp_mst_port is still attached to something
> before trying to use it in order to avoid dereferencing freed memory
> (something that has happened a LOT in the past with this library).
> Because of this it doesn't actually matter whether or not we keep keep
> the ports and branches around in memory as that's not enough, because
> any function that validates the branches and ports passed to it will
> still reject them anyway since they're no longer in the topology
> structure. So, use-after-free errors were fixed but payload deallocation
> was completely broken.
> 
> Two years later, AMD informed me about this issue and I attempted to
> come up with a temporary fix, pending a long-overdue cleanup of this
> library:
> 
> commit c54c7374ff44 ("drm/dp_mst: Skip validating ports during destruction, just ref")
> 
> But then that introduced use-after-free errors, so I quickly reverted
> it:
> 
> commit 9765635b3075 ("Revert "drm/dp_mst: Skip validating ports during destruction, just ref"")
> 
> And in the process, learned that there is just no simple fix for this:
> the design is just broken. Unfortunately, the usage of these helpers are
> quite broken as well. Some drivers like i915 have been smart enough to
> avoid accessing any kind of information from MST port structures, but
> others like nouveau have assumed, understandably so, that
> drm_dp_mst_port structures are normal and can just be accessed at any
> time without worrying about use-after-free errors.
> 
> After a lot of discussion, me and Daniel Vetter came up with a better
> idea to replace all of this.
> 
> To summarize, since this is documented far more indepth in the
> documentation this patch introduces, we make it so that drm_dp_mst_port
> and drm_dp_mst_branch structures have two different classes of
> refcounts: topology_kref, and malloc_kref. topology_kref corresponds to
> the lifetime of the given drm_dp_mst_port or drm_dp_mst_branch in it's
> given topology. Once it hits zero, any associated connectors are removed
> and the branch or port can no longer be validated. malloc_kref
> corresponds to the lifetime of the memory allocation for the actual
> structure, and will always be non-zero so long as the topology_kref is
> non-zero. This gives us a way to allow callers to hold onto port and
> branch device structures past their topology lifetime, and dramatically
> simplifies the lifetimes of both structures. This also finally fixes the
> port deallocation problem, properly.
> 
> Additionally: since this now means that we can keep ports and branch
> devices allocated in memory for however long we need, we no longer need
> a significant amount of the port validation that we currently do.
> 
> Additionally, there is one last scenario that this fixes, which couldn't
> have been fixed properly beforehand:
> 
> - CPU1 unrefs port from topology (refcount 1->0)
> - CPU2 refs port in topology(refcount 0->1)
> 
> Since we now can guarantee memory safety for ports and branches
> as-needed, we also can make our main reference counting functions fix
> this problem by using kref_get_unless_zero() internally so that topology
> refcounts can only ever reach 0 once.
> 
> Changes since v3:
> * Remove rebase detritus - danvet
> * Split out purely style changes into separate patches - hwentlan
> 
> Changes since v2:
> * Fix commit message - checkpatch
> * s/)-1/) - 1/g - checkpatch
> 
> Changes since v1:
> * Remove forward declarations - danvet
> * Move "Branch device and port refcounting" section from documentation
>   into kernel-doc comments - danvet
> * Export internal topology lifetime functions into their own section in
>   the kernel-docs - danvet
> * s/@/&/g for struct references in kernel-docs - danvet
> * Drop the "when they are no longer being used" bits from the kernel
>   docs - danvet
> * Modify diagrams to show how the DRM driver interacts with the topology
>   and payloads - danvet
> * Make suggested documentation changes for
>   drm_dp_mst_topology_get_mstb() and drm_dp_mst_topology_get_port() -
>   danvet
> * Better explain the relationship between malloc refs and topology krefs
>   in the documentation for drm_dp_mst_topology_get_port() and
>   drm_dp_mst_topology_get_mstb() - danvet
> * Fix "See also" in drm_dp_mst_topology_get_mstb() - danvet
> * Rename drm_dp_mst_topology_get_(port|mstb)() ->
>   drm_dp_mst_topology_try_get_(port|mstb)() and
>   drm_dp_mst_topology_ref_(port|mstb)() ->
>   drm_dp_mst_topology_get_(port|mstb)() - danvet
> * s/should/must in docs - danvet
> * WARN_ON(refcount == 0) in topology_get_(mstb|port) - danvet
> * Move kdocs for mstb/port structs inline - danvet
> * Split drm_dp_get_last_connected_port_and_mstb() changes into their own
>   commit - danvet
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Reviewed-by: Harry Wentland <harry.wentland@amd.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: David Airlie <airlied@redhat.com>
> Cc: Jerry Zuo <Jerry.Zuo@amd.com>
> Cc: Juston Li <juston.li@intel.com>
> ---
>  .../gpu/dp-mst/topology-figure-1.dot          |  52 ++
>  .../gpu/dp-mst/topology-figure-2.dot          |  56 +++
>  .../gpu/dp-mst/topology-figure-3.dot          |  59 +++
>  Documentation/gpu/drm-kms-helpers.rst         |  26 +-
>  drivers/gpu/drm/drm_dp_mst_topology.c         | 457 +++++++++++++++---
>  include/drm/drm_dp_mst_helper.h               |  32 +-
>  6 files changed, 613 insertions(+), 69 deletions(-)
>  create mode 100644 Documentation/gpu/dp-mst/topology-figure-1.dot
>  create mode 100644 Documentation/gpu/dp-mst/topology-figure-2.dot
>  create mode 100644 Documentation/gpu/dp-mst/topology-figure-3.dot
> 
> diff --git a/Documentation/gpu/dp-mst/topology-figure-1.dot b/Documentation/gpu/dp-mst/topology-figure-1.dot
> new file mode 100644
> index 000000000000..157e17c7e0b0
> --- /dev/null
> +++ b/Documentation/gpu/dp-mst/topology-figure-1.dot
> @@ -0,0 +1,52 @@
> +digraph T {
> +    /* Make sure our payloads are always drawn below the driver node */
> +    subgraph cluster_driver {
> +        fillcolor = grey;
> +        style = filled;
> +        driver -> {payload1, payload2} [dir=none];
> +    }
> +
> +    /* Driver malloc references */
> +    edge [style=dashed];
> +    driver -> port1;
> +    driver -> port2;
> +    driver -> port3:e;
> +    driver -> port4;
> +
> +    payload1:s -> port1:e;
> +    payload2:s -> port3:e;
> +    edge [style=""];
> +
> +    subgraph cluster_topology {
> +        label="Topology Manager";
> +        labelloc=bottom;
> +
> +        /* Topology references */
> +        mstb1 -> {port1, port2};
> +        port1 -> mstb2;
> +        port2 -> mstb3 -> {port3, port4};
> +        port3 -> mstb4;
> +
> +        /* Malloc references */
> +        edge [style=dashed;dir=back];
> +        mstb1 -> {port1, port2};
> +        port1 -> mstb2;
> +        port2 -> mstb3 -> {port3, port4};
> +        port3 -> mstb4;
> +    }
> +
> +    driver [label="DRM driver";style=filled;shape=box;fillcolor=lightblue];
> +
> +    payload1 [label="Payload #1";style=filled;shape=box;fillcolor=lightblue];
> +    payload2 [label="Payload #2";style=filled;shape=box;fillcolor=lightblue];
> +
> +    mstb1 [label="MSTB #1";style=filled;fillcolor=palegreen;shape=oval];
> +    mstb2 [label="MSTB #2";style=filled;fillcolor=palegreen;shape=oval];
> +    mstb3 [label="MSTB #3";style=filled;fillcolor=palegreen;shape=oval];
> +    mstb4 [label="MSTB #4";style=filled;fillcolor=palegreen;shape=oval];
> +
> +    port1 [label="Port #1";shape=oval];
> +    port2 [label="Port #2";shape=oval];
> +    port3 [label="Port #3";shape=oval];
> +    port4 [label="Port #4";shape=oval];
> +}
> diff --git a/Documentation/gpu/dp-mst/topology-figure-2.dot b/Documentation/gpu/dp-mst/topology-figure-2.dot
> new file mode 100644
> index 000000000000..4243dd1737cb
> --- /dev/null
> +++ b/Documentation/gpu/dp-mst/topology-figure-2.dot
> @@ -0,0 +1,56 @@
> +digraph T {
> +    /* Make sure our payloads are always drawn below the driver node */
> +    subgraph cluster_driver {
> +        fillcolor = grey;
> +        style = filled;
> +        driver -> {payload1, payload2} [dir=none];
> +    }
> +
> +    /* Driver malloc references */
> +    edge [style=dashed];
> +    driver -> port1;
> +    driver -> port2;
> +    driver -> port3:e;
> +    driver -> port4 [color=red];
> +
> +    payload1:s -> port1:e;
> +    payload2:s -> port3:e;
> +    edge [style=""];
> +
> +    subgraph cluster_topology {
> +        label="Topology Manager";
> +        labelloc=bottom;
> +
> +        /* Topology references */
> +        mstb1 -> {port1, port2};
> +        port1 -> mstb2;
> +        edge [color=red];
> +        port2 -> mstb3 -> {port3, port4};
> +        port3 -> mstb4;
> +        edge [color=""];
> +
> +        /* Malloc references */
> +        edge [style=dashed;dir=back];
> +        mstb1 -> {port1, port2};
> +        port1 -> mstb2;
> +        port2 -> mstb3 -> port3;
> +        edge [color=red];
> +        mstb3 -> port4;
> +        port3 -> mstb4;
> +    }
> +
> +    mstb1 [label="MSTB #1";style=filled;fillcolor=palegreen];
> +    mstb2 [label="MSTB #2";style=filled;fillcolor=palegreen];
> +    mstb3 [label="MSTB #3";style=filled;fillcolor=palegreen];
> +    mstb4 [label="MSTB #4";style=filled;fillcolor=grey];
> +
> +    port1 [label="Port #1"];
> +    port2 [label="Port #2"];
> +    port3 [label="Port #3"];
> +    port4 [label="Port #4";style=filled;fillcolor=grey];
> +
> +    driver [label="DRM driver";style=filled;shape=box;fillcolor=lightblue];
> +
> +    payload1 [label="Payload #1";style=filled;shape=box;fillcolor=lightblue];
> +    payload2 [label="Payload #2";style=filled;shape=box;fillcolor=lightblue];
> +}
> diff --git a/Documentation/gpu/dp-mst/topology-figure-3.dot b/Documentation/gpu/dp-mst/topology-figure-3.dot
> new file mode 100644
> index 000000000000..6cd78d06778b
> --- /dev/null
> +++ b/Documentation/gpu/dp-mst/topology-figure-3.dot
> @@ -0,0 +1,59 @@
> +digraph T {
> +    /* Make sure our payloads are always drawn below the driver node */
> +    subgraph cluster_driver {
> +        fillcolor = grey;
> +        style = filled;
> +        edge [dir=none];
> +        driver -> payload1;
> +        driver -> payload2 [penwidth=3];
> +        edge [dir=""];
> +    }
> +
> +    /* Driver malloc references */
> +    edge [style=dashed];
> +    driver -> port1;
> +    driver -> port2;
> +    driver -> port3:e;
> +    driver -> port4 [color=grey];
> +    payload1:s -> port1:e;
> +    payload2:s -> port3:e [penwidth=3];
> +    edge [style=""];
> +
> +    subgraph cluster_topology {
> +        label="Topology Manager";
> +        labelloc=bottom;
> +
> +        /* Topology references */
> +        mstb1 -> {port1, port2};
> +        port1 -> mstb2;
> +        edge [color=grey];
> +        port2 -> mstb3 -> {port3, port4};
> +        port3 -> mstb4;
> +        edge [color=""];
> +
> +        /* Malloc references */
> +        edge [style=dashed;dir=back];
> +        mstb1 -> {port1, port2};
> +        port1 -> mstb2;
> +        port2 -> mstb3 [penwidth=3];
> +        mstb3 -> port3 [penwidth=3];
> +        edge [color=grey];
> +        mstb3 -> port4;
> +        port3 -> mstb4;
> +    }
> +
> +    mstb1 [label="MSTB #1";style=filled;fillcolor=palegreen];
> +    mstb2 [label="MSTB #2";style=filled;fillcolor=palegreen];
> +    mstb3 [label="MSTB #3";style=filled;fillcolor=palegreen;penwidth=3];
> +    mstb4 [label="MSTB #4";style=filled;fillcolor=grey];
> +
> +    port1 [label="Port #1"];
> +    port2 [label="Port #2";penwidth=5];
> +    port3 [label="Port #3";penwidth=3];
> +    port4 [label="Port #4";style=filled;fillcolor=grey];
> +
> +    driver [label="DRM driver";style=filled;shape=box;fillcolor=lightblue];
> +
> +    payload1 [label="Payload #1";style=filled;shape=box;fillcolor=lightblue];
> +    payload2 [label="Payload #2";style=filled;shape=box;fillcolor=lightblue;penwidth=3];
> +}
> diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst
> index b422eb8edf16..7a3fc569bc68 100644
> --- a/Documentation/gpu/drm-kms-helpers.rst
> +++ b/Documentation/gpu/drm-kms-helpers.rst
> @@ -208,18 +208,40 @@ Display Port Dual Mode Adaptor Helper Functions Reference
>  .. kernel-doc:: drivers/gpu/drm/drm_dp_dual_mode_helper.c
>     :export:
>  
> -Display Port MST Helper Functions Reference
> -===========================================
> +Display Port MST Helpers
> +========================
> +
> +Overview
> +--------
>  
>  .. kernel-doc:: drivers/gpu/drm/drm_dp_mst_topology.c
>     :doc: dp mst helper
>  
> +.. kernel-doc:: drivers/gpu/drm/drm_dp_mst_topology.c
> +   :doc: Branch device and port refcounting
> +
> +Functions Reference
> +-------------------
> +
>  .. kernel-doc:: include/drm/drm_dp_mst_helper.h
>     :internal:
>  
>  .. kernel-doc:: drivers/gpu/drm/drm_dp_mst_topology.c
>     :export:
>  
> +Topology Lifetime Internals
> +---------------------------
> +
> +These functions aren't exported to drivers, but are documented here to help make
> +the MST topology helpers easier to understand
> +
> +.. kernel-doc:: drivers/gpu/drm/drm_dp_mst_topology.c
> +   :functions: drm_dp_mst_topology_try_get_mstb drm_dp_mst_topology_get_mstb
> +               drm_dp_mst_topology_put_mstb
> +               drm_dp_mst_topology_try_get_port drm_dp_mst_topology_get_port
> +               drm_dp_mst_topology_put_port
> +               drm_dp_mst_get_mstb_malloc drm_dp_mst_put_mstb_malloc
> +
>  MIPI DSI Helper Functions Reference
>  ===================================
>  
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 074e985093ca..c53cf7eb1dbc 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -850,46 +850,211 @@ static struct drm_dp_mst_branch *drm_dp_add_mst_branch_device(u8 lct, u8 *rad)
>  	if (lct > 1)
>  		memcpy(mstb->rad, rad, lct / 2);
>  	INIT_LIST_HEAD(&mstb->ports);
> -	kref_init(&mstb->kref);
> +	kref_init(&mstb->topology_kref);
> +	kref_init(&mstb->malloc_kref);
>  	return mstb;
>  }
>  
> -static void drm_dp_free_mst_port(struct kref *kref);
> -
>  static void drm_dp_free_mst_branch_device(struct kref *kref)
>  {
> -	struct drm_dp_mst_branch *mstb = container_of(kref, struct drm_dp_mst_branch, kref);
> -	if (mstb->port_parent) {
> -		if (list_empty(&mstb->port_parent->next))
> -			kref_put(&mstb->port_parent->kref, drm_dp_free_mst_port);
> -	}
> +	struct drm_dp_mst_branch *mstb =
> +		container_of(kref, struct drm_dp_mst_branch, malloc_kref);
> +
> +	if (mstb->port_parent)
> +		drm_dp_mst_put_port_malloc(mstb->port_parent);
> +
>  	kfree(mstb);
>  }
>  
> +/**
> + * DOC: Branch device and port refcounting
> + *
> + * Topology refcount overview
> + * ~~~~~~~~~~~~~~~~~~~~~~~~~~
> + *
> + * The refcounting schemes for &struct drm_dp_mst_branch and &struct
> + * drm_dp_mst_port are somewhat unusual. Both ports and branch devices have
> + * two different kinds of refcounts: topology refcounts, and malloc refcounts.
> + *
> + * Topology refcounts are not exposed to drivers, and are handled internally
> + * by the DP MST helpers. The helpers use them in order to prevent the
> + * in-memory topology state from being changed in the middle of critical
> + * operations like changing the internal state of payload allocations. This
> + * means each branch and port will be considered to be connected to the rest
> + * of the topology until it's topology refcount reaches zero. Additionally,
> + * for ports this means that their associated &struct drm_connector will stay
> + * registered with userspace until the port's refcount reaches 0.
> + *
> + * Malloc refcount overview
> + * ~~~~~~~~~~~~~~~~~~~~~~~~
> + *
> + * Malloc references are used to keep a &struct drm_dp_mst_port or &struct
> + * drm_dp_mst_branch allocated even after all of its topology references have
> + * been dropped, so that the driver or MST helpers can safely access each
> + * branch's last known state before it was disconnected from the topology.
> + * When the malloc refcount of a port or branch reaches 0, the memory
> + * allocation containing the &struct drm_dp_mst_branch or &struct
> + * drm_dp_mst_port respectively will be freed.
> + *
> + * For &struct drm_dp_mst_branch, malloc refcounts are not currently exposed
> + * to drivers. As of writing this documentation, there are no drivers that
> + * have a usecase for accessing &struct drm_dp_mst_branch outside of the MST
> + * helpers. Exposing this API to drivers in a race-free manner would take more
> + * tweaking of the refcounting scheme, however patches are welcome provided
> + * there is a legitimate driver usecase for this.
> + *
> + * Refcount relationships in a topology
> + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> + *
> + * Let's take a look at why the relationship between topology and malloc
> + * refcounts is designed the way it is.
> + *
> + * .. kernel-figure:: dp-mst/topology-figure-1.dot
> + *
> + *    An example of topology and malloc refs in a DP MST topology with two
> + *    active payloads. Topology refcount increments are indicated by solid
> + *    lines, and malloc refcount increments are indicated by dashed lines.
> + *    Each starts from the branch which incremented the refcount, and ends at
> + *    the branch to which the refcount belongs to.

I had to take a double take on this one here.  Maybe add ", i.e. the
arrows point the same way as the C pointers used to reference a
structure."

> + *
> + * As you can see in figure 1, every branch increments the topology refcount

Maybe s/figure 1/above figure/, the output doesn't have numbered figures
(and if it did, we'd need an rst reference).

> + * of it's children, and increments the malloc refcount of it's parent.
> + * Additionally, every payload increments the malloc refcount of it's assigned
> + * port by 1.
> + *
> + * So, what would happen if MSTB #3 from the above figure was unplugged from
> + * the system, but the driver hadn't yet removed payload #2 from port #3? The
> + * topology would start to look like figure 2.
> + *
> + * .. kernel-figure:: dp-mst/topology-figure-2.dot
> + *
> + *    Ports and branch devices which have been released from memory are
> + *    colored grey, and references which have been removed are colored red.
> + *
> + * Whenever a port or branch device's topology refcount reaches zero, it will
> + * decrement the topology refcounts of all its children, the malloc refcount
> + * of its parent, and finally its own malloc refcount. For MSTB #4 and port
> + * #4, this means they both have been disconnected from the topology and freed
> + * from memory. But, because payload #2 is still holding a reference to port
> + * #3, port #3 is removed from the topology but it's &struct drm_dp_mst_port
> + * is still accessible from memory. This also means port #3 has not yet
> + * decremented the malloc refcount of MSTB #3, so it's &struct
> + * drm_dp_mst_branch will also stay allocated in memory until port #3's
> + * malloc refcount reaches 0.
> + *
> + * This relationship is necessary because in order to release payload #2, we
> + * need to be able to figure out the last relative of port #3 that's still
> + * connected to the topology. In this case, we would travel up the topology as
> + * shown in figure 3.
> + *
> + * .. kernel-figure:: dp-mst/topology-figure-3.dot
> + *
> + * And finally, remove payload #2 by communicating with port #2 through
> + * sideband transactions.
> + */
> +
> +/**
> + * drm_dp_mst_get_mstb_malloc() - Increment the malloc refcount of a branch
> + * device
> + * @mstb: The &struct drm_dp_mst_branch to increment the malloc refcount of
> + *
> + * Increments &drm_dp_mst_branch.malloc_kref. When
> + * &drm_dp_mst_branch.malloc_kref reaches 0, the memory allocation for @mstb
> + * will be released and @mstb may no longer be used.
> + *
> + * See also: drm_dp_mst_put_mstb_malloc()
> + */
> +static void
> +drm_dp_mst_get_mstb_malloc(struct drm_dp_mst_branch *mstb)
> +{
> +	kref_get(&mstb->malloc_kref);
> +	DRM_DEBUG("mstb %p (%d)\n", mstb, kref_read(&mstb->malloc_kref));
> +}
> +
> +/**
> + * drm_dp_mst_put_mstb_malloc() - Decrement the malloc refcount of a branch
> + * device
> + * @mstb: The &struct drm_dp_mst_branch to decrement the malloc refcount of
> + *
> + * Decrements &drm_dp_mst_branch.malloc_kref. When
> + * &drm_dp_mst_branch.malloc_kref reaches 0, the memory allocation for @mstb
> + * will be released and @mstb may no longer be used.
> + *
> + * See also: drm_dp_mst_get_mstb_malloc()
> + */
> +static void
> +drm_dp_mst_put_mstb_malloc(struct drm_dp_mst_branch *mstb)
> +{
> +	DRM_DEBUG("mstb %p (%d)\n", mstb, kref_read(&mstb->malloc_kref) - 1);
> +	kref_put(&mstb->malloc_kref, drm_dp_free_mst_branch_device);
> +}
> +
> +static void drm_dp_free_mst_port(struct kref *kref)
> +{
> +	struct drm_dp_mst_port *port =
> +		container_of(kref, struct drm_dp_mst_port, malloc_kref);
> +
> +	drm_dp_mst_put_mstb_malloc(port->parent);
> +	kfree(port);
> +}
> +
> +/**
> + * drm_dp_mst_get_port_malloc() - Increment the malloc refcount of an MST port
> + * @port: The &struct drm_dp_mst_port to increment the malloc refcount of
> + *
> + * Increments &drm_dp_mst_port.malloc_kref. When &drm_dp_mst_port.malloc_kref
> + * reaches 0, the memory allocation for @port will be released and @port may
> + * no longer be used.
> + *
> + * Because @port could potentially be freed at any time by the DP MST helpers
> + * if &drm_dp_mst_port.malloc_kref reaches 0, including during a call to this
> + * function, drivers that which to make use of &struct drm_dp_mst_port should
> + * ensure that they grab at least one main malloc reference to their MST ports
> + * in &drm_dp_mst_topology_cbs.add_connector. This callback is called before
> + * there is any chance for &drm_dp_mst_port.malloc_kref to reach 0.
> + *
> + * See also: drm_dp_mst_put_port_malloc()
> + */
> +void
> +drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port)
> +{
> +	kref_get(&port->malloc_kref);
> +	DRM_DEBUG("port %p (%d)\n", port, kref_read(&port->malloc_kref));
> +}
> +EXPORT_SYMBOL(drm_dp_mst_get_port_malloc);
> +
> +/**
> + * drm_dp_mst_put_port_malloc() - Decrement the malloc refcount of an MST port
> + * @port: The &struct drm_dp_mst_port to decrement the malloc refcount of
> + *
> + * Decrements &drm_dp_mst_port.malloc_kref. When &drm_dp_mst_port.malloc_kref
> + * reaches 0, the memory allocation for @port will be released and @port may
> + * no longer be used.
> + *
> + * See also: drm_dp_mst_get_port_malloc()
> + */
> +void
> +drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port)
> +{
> +	DRM_DEBUG("port %p (%d)\n", port, kref_read(&port->malloc_kref) - 1);
> +	kref_put(&port->malloc_kref, drm_dp_free_mst_port);
> +}
> +EXPORT_SYMBOL(drm_dp_mst_put_port_malloc);
> +
>  static void drm_dp_destroy_mst_branch_device(struct kref *kref)
>  {
> -	struct drm_dp_mst_branch *mstb = container_of(kref, struct drm_dp_mst_branch, kref);
> +	struct drm_dp_mst_branch *mstb =
> +		container_of(kref, struct drm_dp_mst_branch, topology_kref);
> +	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
>  	struct drm_dp_mst_port *port, *tmp;
>  	bool wake_tx = false;
>  
> -	/*
> -	 * init kref again to be used by ports to remove mst branch when it is
> -	 * not needed anymore
> -	 */
> -	kref_init(kref);
> -
> -	if (mstb->port_parent && list_empty(&mstb->port_parent->next))
> -		kref_get(&mstb->port_parent->kref);
> -
> -	/*
> -	 * destroy all ports - don't need lock
> -	 * as there are no more references to the mst branch
> -	 * device at this point.
> -	 */
> +	mutex_lock(&mgr->lock);
>  	list_for_each_entry_safe(port, tmp, &mstb->ports, next) {
>  		list_del(&port->next);
>  		drm_dp_mst_topology_put_port(port);
>  	}
> +	mutex_unlock(&mgr->lock);
>  
>  	/* drop any tx slots msg */
>  	mutex_lock(&mstb->mgr->qlock);
> @@ -908,14 +1073,83 @@ static void drm_dp_destroy_mst_branch_device(struct kref *kref)
>  	if (wake_tx)
>  		wake_up_all(&mstb->mgr->tx_waitq);
>  
> -	kref_put(kref, drm_dp_free_mst_branch_device);
> +	drm_dp_mst_put_mstb_malloc(mstb);
>  }
>  
> -static void drm_dp_mst_topology_put_mstb(struct drm_dp_mst_branch *mstb)
> +/**
> + * drm_dp_mst_topology_try_get_mstb() - Increment the topology refcount of a
> + * branch device unless its zero
> + * @mstb: &struct drm_dp_mst_branch to increment the topology refcount of
> + *
> + * Attempts to grab a topology reference to @mstb, if it hasn't yet been
> + * removed from the topology (e.g. &drm_dp_mst_branch.topology_kref has
> + * reached 0). Holding a topology reference implies that a malloc reference
> + * will be held to @mstb as long as the user holds the topology reference.
> + *
> + * Care should be taken to ensure that the user has at least one malloc
> + * reference to @mstb. If you already have a topology reference to @mstb, you
> + * should use drm_dp_mst_topology_get_mstb() instead.
> + *
> + * See also:
> + * drm_dp_mst_topology_get_mstb()
> + * drm_dp_mst_topology_put_mstb()
> + *
> + * Returns:
> + * * 1: A topology reference was grabbed successfully
> + * * 0: @port is no longer in the topology, no reference was grabbed
> + */
> +static int __must_check
> +drm_dp_mst_topology_try_get_mstb(struct drm_dp_mst_branch *mstb)
>  {
> -	kref_put(&mstb->kref, drm_dp_destroy_mst_branch_device);
> +	int ret = kref_get_unless_zero(&mstb->topology_kref);
> +
> +	if (ret)
> +		DRM_DEBUG("mstb %p (%d)\n", mstb,
> +			  kref_read(&mstb->topology_kref));
> +
> +	return ret;
>  }
>  
> +/**
> + * drm_dp_mst_topology_get_mstb() - Increment the topology refcount of a
> + * branch device
> + * @mstb: The &struct drm_dp_mst_branch to increment the topology refcount of
> + *
> + * Increments &drm_dp_mst_branch.topology_refcount without checking whether or
> + * not it's already reached 0. This is only valid to use in scenarios where
> + * you are already guaranteed to have at least one active topology reference
> + * to @mstb. Otherwise, drm_dp_mst_topology_try_get_mstb() must be used.
> + *
> + * See also:
> + * drm_dp_mst_topology_try_get_mstb()
> + * drm_dp_mst_topology_put_mstb()
> + */
> +static void drm_dp_mst_topology_get_mstb(struct drm_dp_mst_branch *mstb)
> +{
> +	WARN_ON(kref_read(&mstb->topology_kref) == 0);
> +	kref_get(&mstb->topology_kref);
> +	DRM_DEBUG("mstb %p (%d)\n", mstb, kref_read(&mstb->topology_kref));
> +}
> +
> +/**
> + * drm_dp_mst_topology_put_mstb() - release a topology reference to a branch
> + * device
> + * @mstb: The &struct drm_dp_mst_branch to release the topology reference from
> + *
> + * Releases a topology reference from @mstb by decrementing
> + * &drm_dp_mst_branch.topology_kref.
> + *
> + * See also:
> + * drm_dp_mst_topology_try_get_mstb()
> + * drm_dp_mst_topology_get_mstb()
> + */
> +static void
> +drm_dp_mst_topology_put_mstb(struct drm_dp_mst_branch *mstb)
> +{
> +	DRM_DEBUG("mstb %p (%d)\n",
> +		  mstb, kref_read(&mstb->topology_kref) - 1);
> +	kref_put(&mstb->topology_kref, drm_dp_destroy_mst_branch_device);
> +}
>  
>  static void drm_dp_port_teardown_pdt(struct drm_dp_mst_port *port, int old_pdt)
>  {
> @@ -937,7 +1171,8 @@ static void drm_dp_port_teardown_pdt(struct drm_dp_mst_port *port, int old_pdt)
>  
>  static void drm_dp_destroy_port(struct kref *kref)
>  {
> -	struct drm_dp_mst_port *port = container_of(kref, struct drm_dp_mst_port, kref);
> +	struct drm_dp_mst_port *port =
> +		container_of(kref, struct drm_dp_mst_port, topology_kref);
>  	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
>  
>  	if (!port->input) {
> @@ -956,7 +1191,6 @@ static void drm_dp_destroy_port(struct kref *kref)
>  			 * from an EDID retrieval */
>  
>  			mutex_lock(&mgr->destroy_connector_lock);
> -			kref_get(&port->parent->kref);
>  			list_add(&port->next, &mgr->destroy_connector_list);
>  			mutex_unlock(&mgr->destroy_connector_lock);
>  			schedule_work(&mgr->destroy_connector_work);
> @@ -967,12 +1201,79 @@ static void drm_dp_destroy_port(struct kref *kref)
>  		drm_dp_port_teardown_pdt(port, port->pdt);
>  		port->pdt = DP_PEER_DEVICE_NONE;
>  	}
> -	kfree(port);
> +	drm_dp_mst_put_port_malloc(port);
> +}
> +
> +/**
> + * drm_dp_mst_topology_try_get_port() - Increment the topology refcount of a
> + * port unless its zero
> + * @port: &struct drm_dp_mst_port to increment the topology refcount of
> + *
> + * Attempts to grab a topology reference to @port, if it hasn't yet been
> + * removed from the topology (e.g. &drm_dp_mst_port.topology_kref has reached
> + * 0). Holding a topology reference implies that a malloc reference will be
> + * held to @port as long as the user holds the topology reference.
> + *
> + * Care should be taken to ensure that the user has at least one malloc
> + * reference to @port. If you already have a topology reference to @port, you
> + * should use drm_dp_mst_topology_get_port() instead.
> + *
> + * See also:
> + * drm_dp_mst_topology_get_port()
> + * drm_dp_mst_topology_put_port()
> + *
> + * Returns:
> + * * 1: A topology reference was grabbed successfully
> + * * 0: @port is no longer in the topology, no reference was grabbed
> + */
> +static int __must_check
> +drm_dp_mst_topology_try_get_port(struct drm_dp_mst_port *port)
> +{
> +	int ret = kref_get_unless_zero(&port->topology_kref);
> +
> +	if (ret)
> +		DRM_DEBUG("port %p (%d)\n", port,
> +			  kref_read(&port->topology_kref));
> +
> +	return ret;
>  }
>  
> +/**
> + * drm_dp_mst_topology_get_port() - Increment the topology refcount of a port
> + * @port: The &struct drm_dp_mst_port to increment the topology refcount of
> + *
> + * Increments &drm_dp_mst_port.topology_refcount without checking whether or
> + * not it's already reached 0. This is only valid to use in scenarios where
> + * you are already guaranteed to have at least one active topology reference
> + * to @port. Otherwise, drm_dp_mst_topology_try_get_port() must be used.
> + *
> + * See also:
> + * drm_dp_mst_topology_try_get_port()
> + * drm_dp_mst_topology_put_port()
> + */
> +static void drm_dp_mst_topology_get_port(struct drm_dp_mst_port *port)
> +{
> +	WARN_ON(kref_read(&port->topology_kref) == 0);
> +	kref_get(&port->topology_kref);
> +	DRM_DEBUG("port %p (%d)\n", port, kref_read(&port->topology_kref));
> +}
> +
> +/**
> + * drm_dp_mst_topology_put_port() - release a topology reference to a port
> + * @port: The &struct drm_dp_mst_port to release the topology reference from
> + *
> + * Releases a topology reference from @port by decrementing
> + * &drm_dp_mst_port.topology_kref.
> + *
> + * See also:
> + * drm_dp_mst_topology_try_get_port()
> + * drm_dp_mst_topology_get_port()
> + */
>  static void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port)
>  {
> -	kref_put(&port->kref, drm_dp_destroy_port);
> +	DRM_DEBUG("port %p (%d)\n",
> +		  port, kref_read(&port->topology_kref) - 1);
> +	kref_put(&port->topology_kref, drm_dp_destroy_port);
>  }
>  
>  static struct drm_dp_mst_branch *
> @@ -981,10 +1282,10 @@ drm_dp_mst_topology_get_mstb_validated_locked(struct drm_dp_mst_branch *mstb,
>  {
>  	struct drm_dp_mst_port *port;
>  	struct drm_dp_mst_branch *rmstb;
> -	if (to_find == mstb) {
> -		kref_get(&mstb->kref);
> +
> +	if (to_find == mstb)
>  		return mstb;
> -	}
> +
>  	list_for_each_entry(port, &mstb->ports, next) {
>  		if (port->mstb) {
>  			rmstb = drm_dp_mst_topology_get_mstb_validated_locked(
> @@ -1001,25 +1302,32 @@ drm_dp_mst_topology_get_mstb_validated(struct drm_dp_mst_topology_mgr *mgr,
>  				       struct drm_dp_mst_branch *mstb)
>  {
>  	struct drm_dp_mst_branch *rmstb = NULL;
> +
>  	mutex_lock(&mgr->lock);
> -	if (mgr->mst_primary)
> +	if (mgr->mst_primary) {
>  		rmstb = drm_dp_mst_topology_get_mstb_validated_locked(
>  		    mgr->mst_primary, mstb);
> +
> +		if (rmstb && !drm_dp_mst_topology_try_get_mstb(rmstb))
> +			rmstb = NULL;
> +	}
>  	mutex_unlock(&mgr->lock);
>  	return rmstb;
>  }
>  
> -static struct drm_dp_mst_port *drm_dp_mst_get_port_ref_locked(struct drm_dp_mst_branch *mstb, struct drm_dp_mst_port *to_find)
> +static struct drm_dp_mst_port *
> +drm_dp_mst_topology_get_port_validated_locked(struct drm_dp_mst_branch *mstb,
> +					      struct drm_dp_mst_port *to_find)
>  {
>  	struct drm_dp_mst_port *port, *mport;
>  
>  	list_for_each_entry(port, &mstb->ports, next) {
> -		if (port == to_find) {
> -			kref_get(&port->kref);
> +		if (port == to_find)
>  			return port;
> -		}
> +
>  		if (port->mstb) {
> -			mport = drm_dp_mst_get_port_ref_locked(port->mstb, to_find);
> +			mport = drm_dp_mst_topology_get_port_validated_locked(
> +			    port->mstb, to_find);
>  			if (mport)
>  				return mport;
>  		}
> @@ -1032,9 +1340,15 @@ drm_dp_mst_topology_get_port_validated(struct drm_dp_mst_topology_mgr *mgr,
>  				       struct drm_dp_mst_port *port)
>  {
>  	struct drm_dp_mst_port *rport = NULL;
> +
>  	mutex_lock(&mgr->lock);
> -	if (mgr->mst_primary)
> -		rport = drm_dp_mst_get_port_ref_locked(mgr->mst_primary, port);
> +	if (mgr->mst_primary) {
> +		rport = drm_dp_mst_topology_get_port_validated_locked(
> +		    mgr->mst_primary, port);
> +
> +		if (rport && !drm_dp_mst_topology_try_get_port(rport))
> +			rport = NULL;
> +	}
>  	mutex_unlock(&mgr->lock);
>  	return rport;
>  }
> @@ -1042,11 +1356,12 @@ drm_dp_mst_topology_get_port_validated(struct drm_dp_mst_topology_mgr *mgr,
>  static struct drm_dp_mst_port *drm_dp_get_port(struct drm_dp_mst_branch *mstb, u8 port_num)
>  {
>  	struct drm_dp_mst_port *port;
> +	int ret;
>  
>  	list_for_each_entry(port, &mstb->ports, next) {
>  		if (port->port_num == port_num) {
> -			kref_get(&port->kref);
> -			return port;
> +			ret = drm_dp_mst_topology_try_get_port(port);
> +			return ret ? port : NULL;
>  		}
>  	}
>  
> @@ -1095,6 +1410,11 @@ static bool drm_dp_port_setup_pdt(struct drm_dp_mst_port *port)
>  		if (port->mstb) {
>  			port->mstb->mgr = port->mgr;
>  			port->mstb->port_parent = port;
> +			/*
> +			 * Make sure this port's memory allocation stays
> +			 * around until it's child MSTB releases it
> +			 */
> +			drm_dp_mst_get_port_malloc(port);
>  
>  			send_link = true;
>  		}
> @@ -1155,17 +1475,26 @@ static void drm_dp_add_port(struct drm_dp_mst_branch *mstb,
>  	bool created = false;
>  	int old_pdt = 0;
>  	int old_ddps = 0;
> +
>  	port = drm_dp_get_port(mstb, port_msg->port_number);
>  	if (!port) {
>  		port = kzalloc(sizeof(*port), GFP_KERNEL);
>  		if (!port)
>  			return;
> -		kref_init(&port->kref);
> +		kref_init(&port->topology_kref);
> +		kref_init(&port->malloc_kref);
>  		port->parent = mstb;
>  		port->port_num = port_msg->port_number;
>  		port->mgr = mstb->mgr;
>  		port->aux.name = "DPMST";
>  		port->aux.dev = dev->dev;
> +
> +		/*
> +		 * Make sure the memory allocation for our parent branch stays
> +		 * around until our own memory allocation is released
> +		 */
> +		drm_dp_mst_get_mstb_malloc(mstb);
> +
>  		created = true;
>  	} else {
>  		old_pdt = port->pdt;
> @@ -1185,7 +1514,7 @@ static void drm_dp_add_port(struct drm_dp_mst_branch *mstb,
>  	   for this list */
>  	if (created) {
>  		mutex_lock(&mstb->mgr->lock);
> -		kref_get(&port->kref);
> +		drm_dp_mst_topology_get_port(port);
>  		list_add(&port->next, &mstb->ports);
>  		mutex_unlock(&mstb->mgr->lock);
>  	}
> @@ -1284,7 +1613,7 @@ static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_
>  {
>  	struct drm_dp_mst_branch *mstb;
>  	struct drm_dp_mst_port *port;
> -	int i;
> +	int i, ret;
>  	/* find the port by iterating down */
>  
>  	mutex_lock(&mgr->lock);
> @@ -1309,7 +1638,9 @@ static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_
>  			}
>  		}
>  	}
> -	kref_get(&mstb->kref);
> +	ret = drm_dp_mst_topology_try_get_mstb(mstb);
> +	if (!ret)
> +		mstb = NULL;
>  out:
>  	mutex_unlock(&mgr->lock);
>  	return mstb;
> @@ -1344,14 +1675,17 @@ drm_dp_get_mst_branch_device_by_guid(struct drm_dp_mst_topology_mgr *mgr,
>  				     uint8_t *guid)
>  {
>  	struct drm_dp_mst_branch *mstb;
> +	int ret;
>  
>  	/* find the port by iterating down */
>  	mutex_lock(&mgr->lock);
>  
>  	mstb = get_mst_branch_device_by_guid_helper(mgr->mst_primary, guid);
> -
> -	if (mstb)
> -		kref_get(&mstb->kref);
> +	if (mstb) {
> +		ret = drm_dp_mst_topology_try_get_mstb(mstb);
> +		if (!ret)
> +			mstb = NULL;
> +	}
>  
>  	mutex_unlock(&mgr->lock);
>  	return mstb;
> @@ -1390,11 +1724,14 @@ static void drm_dp_mst_link_probe_work(struct work_struct *work)
>  {
>  	struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct drm_dp_mst_topology_mgr, work);
>  	struct drm_dp_mst_branch *mstb;
> +	int ret;
>  
>  	mutex_lock(&mgr->lock);
>  	mstb = mgr->mst_primary;
>  	if (mstb) {
> -		kref_get(&mstb->kref);
> +		ret = drm_dp_mst_topology_try_get_mstb(mstb);
> +		if (!ret)
> +			mstb = NULL;
>  	}
>  	mutex_unlock(&mgr->lock);
>  	if (mstb) {
> @@ -1722,8 +2059,10 @@ static struct drm_dp_mst_branch *drm_dp_get_last_connected_port_and_mstb(struct
>  
>  		if (found_port) {
>  			rmstb = found_port->parent;
> -			kref_get(&rmstb->kref);
> -			*port_num = found_port->port_num;
> +			if (drm_dp_mst_topology_try_get_mstb(rmstb))
> +				*port_num = found_port->port_num;
> +			else
> +				rmstb = NULL;
>  		}
>  	}
>  	mutex_unlock(&mgr->lock);
> @@ -2176,7 +2515,7 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
>  
>  		/* give this the main reference */
>  		mgr->mst_primary = mstb;
> -		kref_get(&mgr->mst_primary->kref);
> +		drm_dp_mst_topology_get_mstb(mgr->mst_primary);
>  
>  		ret = drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
>  							 DP_MST_EN | DP_UP_REQ_EN | DP_UPSTREAM_IS_SRC);
> @@ -3096,13 +3435,6 @@ static void drm_dp_tx_work(struct work_struct *work)
>  	mutex_unlock(&mgr->qlock);
>  }
>  
> -static void drm_dp_free_mst_port(struct kref *kref)
> -{
> -	struct drm_dp_mst_port *port = container_of(kref, struct drm_dp_mst_port, kref);
> -	kref_put(&port->parent->kref, drm_dp_free_mst_branch_device);
> -	kfree(port);
> -}
> -
>  static void drm_dp_destroy_connector_work(struct work_struct *work)
>  {
>  	struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct drm_dp_mst_topology_mgr, destroy_connector_work);
> @@ -3123,7 +3455,6 @@ static void drm_dp_destroy_connector_work(struct work_struct *work)
>  		list_del(&port->next);
>  		mutex_unlock(&mgr->destroy_connector_lock);
>  
> -		kref_init(&port->kref);
>  		INIT_LIST_HEAD(&port->next);
>  
>  		mgr->cbs->destroy_connector(mgr, port->connector);
> @@ -3137,7 +3468,7 @@ static void drm_dp_destroy_connector_work(struct work_struct *work)
>  			drm_dp_mst_put_payload_id(mgr, port->vcpi.vcpi);
>  		}
>  
> -		kref_put(&port->kref, drm_dp_free_mst_port);
> +		drm_dp_mst_put_port_malloc(port);
>  		send_hotplug = true;
>  	}
>  	if (send_hotplug)
> diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
> index 371cc2816477..8eca5f29242c 100644
> --- a/include/drm/drm_dp_mst_helper.h
> +++ b/include/drm/drm_dp_mst_helper.h
> @@ -44,7 +44,6 @@ struct drm_dp_vcpi {
>  
>  /**
>   * struct drm_dp_mst_port - MST port
> - * @kref: reference count for this port.
>   * @port_num: port number
>   * @input: if this port is an input port.
>   * @mcs: message capability status - DP 1.2 spec.
> @@ -67,7 +66,18 @@ struct drm_dp_vcpi {
>   * in the MST topology.
>   */
>  struct drm_dp_mst_port {
> -	struct kref kref;
> +	/**
> +	 * @topology_kref: refcount for this port's lifetime in the topology,
> +	 * only the DP MST helpers should need to touch this
> +	 */
> +	struct kref topology_kref;
> +
> +	/**
> +	 * @malloc_kref: refcount for the memory allocation containing this
> +	 * structure. See drm_dp_mst_get_port_malloc() and
> +	 * drm_dp_mst_put_port_malloc().
> +	 */
> +	struct kref malloc_kref;
>  
>  	u8 port_num;
>  	bool input;
> @@ -102,7 +112,6 @@ struct drm_dp_mst_port {
>  
>  /**
>   * struct drm_dp_mst_branch - MST branch device.
> - * @kref: reference count for this port.
>   * @rad: Relative Address to talk to this branch device.
>   * @lct: Link count total to talk to this branch device.
>   * @num_ports: number of ports on the branch.
> @@ -121,7 +130,19 @@ struct drm_dp_mst_port {
>   * to downstream port of parent branches.
>   */
>  struct drm_dp_mst_branch {
> -	struct kref kref;
> +	/**
> +	 * @topology_kref: refcount for this branch device's lifetime in the
> +	 * topology, only the DP MST helpers should need to touch this
> +	 */
> +	struct kref topology_kref;
> +
> +	/**
> +	 * @malloc_kref: refcount for the memory allocation containing this
> +	 * structure. See drm_dp_mst_get_mstb_malloc() and
> +	 * drm_dp_mst_put_mstb_malloc().
> +	 */
> +	struct kref malloc_kref;
> +
>  	u8 rad[8];
>  	u8 lct;
>  	int num_ports;
> @@ -626,4 +647,7 @@ int drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
>  int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
>  				 struct drm_dp_mst_port *port, bool power_up);
>  
> +void drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port);
> +void drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port);
> +


_Really_ nice documentation, and the graphs look pretty!

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Aside: We're lacking kerneldoc for drm_dp_mst_topology_cbs. A follow-up to
document a bit what drivers are expected to do in each callback would be
neat.
-Daniel


>  #endif
> -- 
> 2.20.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH v5 07/20] drm/dp_mst: Restart last_connected_port_and_mstb() if topology ref fails

[Daniel Vetter]

On Tue, Jan 08, 2019 at 07:35:04PM -0500, Lyude Paul wrote:
> While this isn't a complete fix, this will improve the reliability of
> drm_dp_get_last_connected_port_and_mstb() pretty significantly during
> hotplug events, since there's a chance that the in-memory topology tree
> may not be fully updated when drm_dp_get_last_connected_port_and_mstb()
> is called and thus might end up causing our search to fail on an mstb
> whose topology refcount has reached 0, but has not yet been removed from
> it's parent.
> 
> Ideally, we should further fix this problem by ensuring that we deal
> with the potential for racing with a hotplug event, which would look
> like this:
> 
> * drm_dp_payload_send_msg() retrieves the last living relative of mstb
>   with drm_dp_get_last_connected_port_and_mstb()
> * drm_dp_payload_send_msg() starts building payload message
>   At the same time, mstb gets unplugged from the topology and is no
>   longer the actual last living relative of the original mstb
> * drm_dp_payload_send_msg() tries sending the payload message, hub times
>   out
> * Hub timed out, we give up and run away-resulting in the payload being
>   leaked
> 
> This could be fixed by restarting the
> drm_dp_get_last_connected_port_and_mstb() search whenever we get a
> timeout, sending the payload to the new mstb, then repeating until
> either the entire topology is removed from the system or
> drm_dp_get_last_connected_port_and_mstb() fails. But since the above
> race condition is not terribly likely, we'll address that in a later
> patch series once we've improved the recovery handling for VCPI
> allocations in the rest of the DP MST helpers.
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Reviewed-by: Harry Wentland <harry.wentland@amd.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: David Airlie <airlied@redhat.com>
> Cc: Jerry Zuo <Jerry.Zuo@amd.com>
> Cc: Juston Li <juston.li@intel.com>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 54 ++++++++++++++++++++++-----
>  1 file changed, 44 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index c53cf7eb1dbc..bafc85f08606 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -2047,24 +2047,50 @@ static struct drm_dp_mst_port *drm_dp_get_last_connected_port_to_mstb(struct drm
>  	return drm_dp_get_last_connected_port_to_mstb(mstb->port_parent->parent);
>  }
>  
> -static struct drm_dp_mst_branch *drm_dp_get_last_connected_port_and_mstb(struct drm_dp_mst_topology_mgr *mgr,
> -									 struct drm_dp_mst_branch *mstb,
> -									 int *port_num)
> +/**
> + * drm_dp_get_last_connected_port_and_mstb() - Find the last living relatives
> + * in a topology of a given branch device
> + * @mgr: The topology manager to use
> + * @mstb: The disconnected branch device
> + * @port_num: Where to store the number of the last connected port
> + *
> + * Searches upwards in the topology starting from @mstb to try to find the
> + * closest available parent of @mstb that's still connected to the rest of the
> + * topology. This can be used in order to perform operations like releasing
> + * payloads, where the branch device which owned the payload may no longer be
> + * around and thus would require that the payload on the last living relative
> + * be freed instead.
> + *
> + * Returns:
> + * The last connected &drm_dp_mst_branch in the topology that was a parent of
> + * @mstb, if there is one.
> + */

Since this is an internal function and we don't pull it into the kerneldoc
there's a good chance the details will bitrot (since 0day won't spot when
e.g. the arguments change). It'd just keep a small explaining why we need
to do this and drop the other bits. Either way:

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>


> +static struct drm_dp_mst_branch *
> +drm_dp_get_last_connected_port_and_mstb(struct drm_dp_mst_topology_mgr *mgr,
> +					struct drm_dp_mst_branch *mstb,
> +					int *port_num)
>  {
>  	struct drm_dp_mst_branch *rmstb = NULL;
>  	struct drm_dp_mst_port *found_port;
> +
>  	mutex_lock(&mgr->lock);
> -	if (mgr->mst_primary) {
> +	if (!mgr->mst_primary)
> +		goto out;
> +
> +	do {
>  		found_port = drm_dp_get_last_connected_port_to_mstb(mstb);
> +		if (!found_port)
> +			break;
>  
> -		if (found_port) {
> +		if (drm_dp_mst_topology_try_get_mstb(found_port->parent)) {
>  			rmstb = found_port->parent;
> -			if (drm_dp_mst_topology_try_get_mstb(rmstb))
> -				*port_num = found_port->port_num;
> -			else
> -				rmstb = NULL;
> +			*port_num = found_port->port_num;
> +		} else {
> +			/* Search again, starting from this parent */
> +			mstb = found_port->parent;
>  		}
> -	}
> +	} while (!rmstb);
> +out:
>  	mutex_unlock(&mgr->lock);
>  	return rmstb;
>  }
> @@ -2113,6 +2139,14 @@ static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
>  
>  	drm_dp_queue_down_tx(mgr, txmsg);
>  
> +	/*
> +	 * FIXME: there is a small chance that between getting the last
> +	 * connected mstb and sending the payload message, the last connected
> +	 * mstb could also be removed from the topology. In the future, this
> +	 * needs to be fixed by restarting the
> +	 * drm_dp_get_last_connected_port_and_mstb() search in the event of a
> +	 * timeout if the topology is still connected to the system.
> +	 */
>  	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
>  	if (ret > 0) {
>  		if (txmsg->reply.reply_type == 1)
> -- 
> 2.20.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH v5 04/20] drm/dp_mst: Fix some formatting in drm_dp_mst_deallocate_vcpi()

[Daniel Vetter]

On Tue, Jan 08, 2019 at 07:35:01PM -0500, Lyude Paul wrote:
> Split some stuff across multiple lines
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Reviewed-by: Harry Wentland <harry.wentland@amd.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: David Airlie <airlied@redhat.com>
> Cc: Jerry Zuo <Jerry.Zuo@amd.com>
> Cc: Juston Li <juston.li@intel.com>

On patches 1-4: Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index a63a4d32962a..75cca6a843fb 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -2790,7 +2790,8 @@ EXPORT_SYMBOL(drm_dp_mst_reset_vcpi_slots);
>   * @mgr: manager for this port
>   * @port: unverified port to deallocate vcpi for
>   */
> -void drm_dp_mst_deallocate_vcpi(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port)
> +void drm_dp_mst_deallocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
> +				struct drm_dp_mst_port *port)
>  {
>  	port = drm_dp_get_validated_port_ref(mgr, port);
>  	if (!port)
> -- 
> 2.20.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH v5 08/20] drm/dp_mst: Stop releasing VCPI when removing ports from topology

[Daniel Vetter]

On Tue, Jan 08, 2019 at 07:35:05PM -0500, Lyude Paul wrote:
> This has never actually worked, and isn't needed anyway: the driver's
> always going to try to deallocate VCPI when it tears down the display
> that the VCPI belongs to.
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Reviewed-by: Harry Wentland <harry.wentland@amd.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: David Airlie <airlied@redhat.com>
> Cc: Jerry Zuo <Jerry.Zuo@amd.com>
> Cc: Juston Li <juston.li@intel.com>

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index bafc85f08606..8088527a7aea 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -1176,8 +1176,6 @@ static void drm_dp_destroy_port(struct kref *kref)
>  	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
>  
>  	if (!port->input) {
> -		port->vcpi.num_slots = 0;
> -
>  		kfree(port->cached_edid);
>  
>  		/*
> @@ -3496,12 +3494,6 @@ static void drm_dp_destroy_connector_work(struct work_struct *work)
>  		drm_dp_port_teardown_pdt(port, port->pdt);
>  		port->pdt = DP_PEER_DEVICE_NONE;
>  
> -		if (!port->input && port->vcpi.vcpi > 0) {
> -			drm_dp_mst_reset_vcpi_slots(mgr, port);
> -			drm_dp_update_payload_part1(mgr);
> -			drm_dp_mst_put_payload_id(mgr, port->vcpi.vcpi);
> -		}
> -
>  		drm_dp_mst_put_port_malloc(port);
>  		send_hotplug = true;
>  	}
> -- 
> 2.20.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH v5 17/20] drm/dp_mst: Add some atomic state iterator macros

[Daniel Vetter]

On Tue, Jan 08, 2019 at 07:35:14PM -0500, Lyude Paul wrote:
> Changes since v6:
>  - Move EXPORT_SYMBOL() for drm_dp_mst_topology_state_funcs to this
>    commit
>  - Document __drm_dp_mst_state_iter_get() and note that it shouldn't be
>    called directly
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: David Airlie <airlied@redhat.com>
> Cc: Jerry Zuo <Jerry.Zuo@amd.com>
> Cc: Harry Wentland <harry.wentland@amd.com>
> Cc: Juston Li <juston.li@intel.com>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c |  5 +-
>  include/drm/drm_dp_mst_helper.h       | 96 +++++++++++++++++++++++++++
>  2 files changed, 99 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index efd8fa29fff6..370371145cdd 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -3530,10 +3530,11 @@ static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
>  	kfree(mst_state);
>  }
>  
> -static const struct drm_private_state_funcs mst_state_funcs = {
> +const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs = {
>  	.atomic_duplicate_state = drm_dp_mst_duplicate_state,
>  	.atomic_destroy_state = drm_dp_mst_destroy_state,
>  };
> +EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);
>  
>  /**
>   * drm_atomic_get_mst_topology_state: get MST topology state
> @@ -3617,7 +3618,7 @@ int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr,
>  
>  	drm_atomic_private_obj_init(dev, &mgr->base,
>  				    &mst_state->base,
> -				    &mst_state_funcs);
> +				    &drm_dp_mst_topology_state_funcs);
>  
>  	return 0;
>  }
> diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
> index 8eca5f29242c..581163c8d7d7 100644
> --- a/include/drm/drm_dp_mst_helper.h
> +++ b/include/drm/drm_dp_mst_helper.h
> @@ -650,4 +650,100 @@ int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
>  void drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port);
>  void drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port);
>  
> +extern const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs;
> +
> +/**
> + * __drm_dp_mst_state_iter_get - private atomic state iterator function for
> + * macro-internal use
> + * @state: &struct drm_atomic_state pointer
> + * @mgr: pointer to the &struct drm_dp_mst_topology_mgr iteration cursor
> + * @old_state: optional pointer to the old &struct drm_dp_mst_topology_state
> + * iteration cursor
> + * @new_state: optional pointer to the new &struct drm_dp_mst_topology_state
> + * iteration cursor
> + * @i: int iteration cursor, for macro-internal use
> + *
> + * Used by for_each_oldnew_mst_mgr_in_state(),
> + * for_each_old_mst_mgr_in_state(), and for_each_new_mst_mgr_in_state(). Don't
> + * call this directly.
> + *
> + * Returns:
> + * True if the current &struct drm_private_obj is a &struct
> + * drm_dp_mst_topology_mgr, false otherwise.
> + */
> +static inline bool
> +__drm_dp_mst_state_iter_get(struct drm_atomic_state *state,
> +			    struct drm_dp_mst_topology_mgr **mgr,
> +			    struct drm_dp_mst_topology_state **old_state,
> +			    struct drm_dp_mst_topology_state **new_state,
> +			    int i)
> +{
> +	struct __drm_private_objs_state *objs_state = &state->private_objs[i];
> +
> +	if (objs_state->ptr->funcs != &drm_dp_mst_topology_state_funcs)
> +		return false;
> +
> +	*mgr = to_dp_mst_topology_mgr(objs_state->ptr);
> +	if (old_state)
> +		*old_state = to_dp_mst_topology_state(objs_state->old_state);
> +	if (new_state)
> +		*new_state = to_dp_mst_topology_state(objs_state->new_state);
> +
> +	return true;
> +}
> +
> +/**
> + * for_each_oldnew_mst_mgr_in_state - iterate over all DP MST topology
> + * managers in an atomic update
> + * @__state: &struct drm_atomic_state pointer
> + * @mgr: &struct drm_dp_mst_topology_mgr iteration cursor
> + * @old_state: &struct drm_dp_mst_topology_state iteration cursor for the old
> + * state
> + * @new_state: &struct drm_dp_mst_topology_state iteration cursor for the new
> + * state
> + * @__i: int iteration cursor, for macro-internal use
> + *
> + * This iterates over all DRM DP MST topology managers in an atomic update,
> + * tracking both old and new state. This is useful in places where the state
> + * delta needs to be considered, for example in atomic check functions.
> + */
> +#define for_each_oldnew_mst_mgr_in_state(__state, mgr, old_state, new_state, __i) \
> +	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
> +		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), &(old_state), &(new_state), (__i)))
> +
> +/**
> + * for_each_old_mst_mgr_in_state - iterate over all DP MST topology managers
> + * in an atomic update
> + * @__state: &struct drm_atomic_state pointer
> + * @mgr: &struct drm_dp_mst_topology_mgr iteration cursor
> + * @old_state: &struct drm_dp_mst_topology_state iteration cursor for the old
> + * state
> + * @__i: int iteration cursor, for macro-internal use
> + *
> + * This iterates over all DRM DP MST topology managers in an atomic update,
> + * tracking only the old state. This is useful in disable functions, where we
> + * need the old state the hardware is still in.
> + */
> +#define for_each_old_mst_mgr_in_state(__state, mgr, old_state, __i) \
> +	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
> +		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), &(old_state), NULL, (__i)))
> +
> +/**
> + * for_each_new_mst_mgr_in_state - iterate over all DP MST topology managers
> + * in an atomic update
> + * @__state: &struct drm_atomic_state pointer
> + * @mgr: &struct drm_dp_mst_topology_mgr iteration cursor
> + * @new_state: &struct drm_dp_mst_topology_state iteration cursor for the new
> + * state
> + * @__i: int iteration cursor, for macro-internal use
> + *
> + * This iterates over all DRM DP MST topology managers in an atomic update,
> + * tracking only the new state. This is useful in enable functions, where we
> + * need the new state the hardware should be in when the atomic commit
> + * operation has completed.
> + */
> +#define for_each_new_mst_mgr_in_state(__state, mgr, new_state, __i) \
> +	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
> +		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), NULL, &(new_state), (__i)))

Since we only need this iterator here, and only in drm_dp_mst_topology.c I
think you could also just open code them in the single user (and then
maybe squash that in with one). Either way

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> +
>  #endif
> -- 
> 2.20.1
> 

-- 
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Re: [PATCH v5 18/20] drm/dp_mst: Start tracking per-port VCPI allocations

[Daniel Vetter]

On Tue, Jan 08, 2019 at 07:35:15PM -0500, Lyude Paul wrote:
> There has been a TODO waiting for quite a long time in
> drm_dp_mst_topology.c:
> 
> 	/* We cannot rely on port->vcpi.num_slots to update
> 	 * topology_state->avail_slots as the port may not exist if the parent
> 	 * branch device was unplugged. This should be fixed by tracking
> 	 * per-port slot allocation in drm_dp_mst_topology_state instead of
> 	 * depending on the caller to tell us how many slots to release.
> 	 */
> 
> That's not the only reason we should fix this: forcing the driver to
> track the VCPI allocations throughout a state's atomic check is
> error prone, because it means that extra care has to be taken with the
> order that drm_dp_atomic_find_vcpi_slots() and
> drm_dp_atomic_release_vcpi_slots() are called in in order to ensure
> idempotency. Currently the only driver actually using these helpers,
> i915, doesn't even do this correctly: multiple ->best_encoder() checks
> with i915's current implementation would not be idempotent and would
> over-allocate VCPI slots, something I learned trying to implement
> fallback retraining in MST.
> 
> So: simplify this whole mess, and teach drm_dp_atomic_find_vcpi_slots()
> and drm_dp_atomic_release_vcpi_slots() to track the VCPI allocations for
> each port. This allows us to ensure idempotency without having to rely
> on the driver as much. Additionally: the driver doesn't need to do any
> kind of VCPI slot tracking anymore if it doesn't need it for it's own
> internal state.
> 
> Additionally; this adds a new drm_dp_mst_atomic_check() helper which
> must be used by atomic drivers to perform validity checks for the new
> VCPI allocations incurred by a state.
> 
> Also: update the documentation and make it more obvious that these
> /must/ be called by /all/ atomic drivers supporting MST.
> 
> Changes since v9:
> * Add some missing changes that were requested by danvet that I forgot
>   about after I redid all of the kref stuff:
>   * Remove unnecessary state changes in intel_dp_mst_atomic_check
>   * Cleanup atomic check logic for VCPI allocations - all we need to check in
>     compute_config is whether or not this state disables a CRTC, then free
>     VCPI based off that
> 
> Changes since v8:
>  * Fix compile errors, whoops!
> 
> Changes since v7:
>  - Don't check for mixed stale/valid VCPI allocations, just rely on
>  connector registration to stop such erroneous modesets
> 
> Changes since v6:
>  - Keep a kref to all of the ports we have allocations on. This required
>    a good bit of changing to when we call drm_dp_find_vcpi_slots(),
>    mainly that we need to ensure that we only redo VCPI allocations on
>    actual mode or CRTC changes, not crtc_state->active changes.
>    Additionally, we no longer take the registration of the DRM connector
>    for each port into account because so long as we have a kref to the
>    port in the new or previous atomic state, the connector will stay
>    registered.
>  - Use the small changes to drm_dp_put_port() to add even more error
>    checking to make misusage of the helpers more obvious. I added this
>    after having to chase down various use-after-free conditions that
>    started popping up from the new helpers so no one else has to
>    troubleshoot that.
>  - Move some accidental DRM_DEBUG_KMS() calls to DRM_DEBUG_ATOMIC()
>  - Update documentation again, note that find/release() should both not be
>    called on the same port in a single atomic check phase (but multiple
>    calls to one or the other is OK)
> 
> Changes since v4:
>  - Don't skip the atomic checks for VCPI allocations if no new VCPI
>    allocations happen in a state. This makes the next change I'm about
>    to list here a lot easier to implement.
>  - Don't ignore VCPI allocations on destroyed ports, instead ensure that
>    when ports are destroyed and still have VCPI allocations in the
>    topology state, the only state changes allowed are releasing said
>    ports' VCPI. This prevents a state with a mix of VCPI allocations
>    from destroyed ports, and allocations from valid ports.
> 
> Changes since v3:
>  - Don't release VCPI allocations in the topology state immediately in
>    drm_dp_atomic_release_vcpi_slots(), instead mark them as 0 and skip
>    over them in drm_dp_mst_duplicate_state(). This makes it so
>    drm_dp_atomic_release_vcpi_slots() is still idempotent while also
>    throwing warnings if the driver messes up it's book keeping and tries
>    to release VCPI slots on a port that doesn't have any pre-existing
>    VCPI allocation - danvet
>  - Change mst_state/state in some debugging messages to "mst state"
> 
> Changes since v2:
>  - Use kmemdup() for duplicating MST state - danvet
>  - Move port validation out of duplicate state callback - danvet
>  - Handle looping through MST topology states in
>    drm_dp_mst_atomic_check() so the driver doesn't have to do it
>  - Fix documentation in drm_dp_atomic_find_vcpi_slots()
>  - Move the atomic check for each individual topology state into it's
>    own function, reduces indenting
>  - Don't consider "stale" MST ports when calculating the bandwidth
>    requirements. This is needed because originally we relied on the
>    state duplication functions to prune any stale ports from the new
>    state, which would prevent us from incorrectly considering their
>    bandwidth requirements alongside legitimate new payloads.
>  - Add function references in drm_dp_atomic_release_vcpi_slots() - danvet
>  - Annotate atomic VCPI and atomic check functions with __must_check
>    - danvet
> 
> Changes since v1:
>  - Don't use the now-removed ->atomic_check() for private objects hook,
>    just give drivers a function to call themselves
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: David Airlie <airlied@redhat.com>
> Cc: Jerry Zuo <Jerry.Zuo@amd.com>
> Cc: Harry Wentland <harry.wentland@amd.com>
> Cc: Juston Li <juston.li@intel.com>

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 247 ++++++++++++++++++++++----
>  drivers/gpu/drm/i915/intel_display.c  |   4 +
>  drivers/gpu/drm/i915/intel_dp_mst.c   |  54 +++---
>  include/drm/drm_dp_mst_helper.h       |  23 ++-
>  4 files changed, 266 insertions(+), 62 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 370371145cdd..fc778c6d487e 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -3020,21 +3020,42 @@ static int drm_dp_init_vcpi(struct drm_dp_mst_topology_mgr *mgr,
>  }
>  
>  /**
> - * drm_dp_atomic_find_vcpi_slots() - Find and add vcpi slots to the state
> + * drm_dp_atomic_find_vcpi_slots() - Find and add VCPI slots to the state
>   * @state: global atomic state
>   * @mgr: MST topology manager for the port
>   * @port: port to find vcpi slots for
>   * @pbn: bandwidth required for the mode in PBN
>   *
> - * RETURNS:
> - * Total slots in the atomic state assigned for this port or error
> + * Allocates VCPI slots to @port, replacing any previous VCPI allocations it
> + * may have had. Any atomic drivers which support MST must call this function
> + * in their &drm_encoder_helper_funcs.atomic_check() callback to change the
> + * current VCPI allocation for the new state, but only when
> + * &drm_crtc_state.mode_changed or &drm_crtc_state.connectors_changed is set
> + * to ensure compatibility with userspace applications that still use the
> + * legacy modesetting UAPI.
> + *
> + * Allocations set by this function are not checked against the bandwidth
> + * restraints of @mgr until the driver calls drm_dp_mst_atomic_check().
> + *
> + * Additionally, it is OK to call this function multiple times on the same
> + * @port as needed. It is not OK however, to call this function and
> + * drm_dp_atomic_release_vcpi_slots() in the same atomic check phase.
> + *
> + * See also:
> + * drm_dp_atomic_release_vcpi_slots()
> + * drm_dp_mst_atomic_check()
> + *
> + * Returns:
> + * Total slots in the atomic state assigned for this port, or a negative error
> + * code if the port no longer exists
>   */
>  int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
>  				  struct drm_dp_mst_topology_mgr *mgr,
>  				  struct drm_dp_mst_port *port, int pbn)
>  {
>  	struct drm_dp_mst_topology_state *topology_state;
> -	int req_slots;
> +	struct drm_dp_vcpi_allocation *pos, *vcpi = NULL;
> +	int prev_slots, req_slots, ret;
>  
>  	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
>  	if (IS_ERR(topology_state))
> @@ -3043,20 +3064,54 @@ int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
>  	port = drm_dp_mst_topology_get_port_validated(mgr, port);
>  	if (port == NULL)
>  		return -EINVAL;
> -	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
> -	DRM_DEBUG_KMS("vcpi slots req=%d, avail=%d\n",
> -			req_slots, topology_state->avail_slots);
>  
> -	if (req_slots > topology_state->avail_slots) {
> -		drm_dp_mst_topology_put_port(port);
> -		return -ENOSPC;
> +	/* Find the current allocation for this port, if any */
> +	list_for_each_entry(pos, &topology_state->vcpis, next) {
> +		if (pos->port == port) {
> +			vcpi = pos;
> +			prev_slots = vcpi->vcpi;
> +
> +			/*
> +			 * This should never happen, unless the driver tries
> +			 * releasing and allocating the same VCPI allocation,
> +			 * which is an error
> +			 */
> +			if (WARN_ON(!prev_slots)) {
> +				DRM_ERROR("cannot allocate and release VCPI on [MST PORT:%p] in the same state\n",
> +					  port);
> +				return -EINVAL;
> +			}
> +
> +			break;
> +		}
>  	}
> +	if (!vcpi)
> +		prev_slots = 0;
> +
> +	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
> +
> +	DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] [MST PORT:%p] VCPI %d -> %d\n",
> +			 port->connector->base.id, port->connector->name,
> +			 port, prev_slots, req_slots);
> +
> +	/* Add the new allocation to the state */
> +	if (!vcpi) {
> +		vcpi = kzalloc(sizeof(*vcpi), GFP_KERNEL);
> +		if (!vcpi) {
> +			ret = -ENOMEM;
> +			goto out;
> +		}
>  
> -	topology_state->avail_slots -= req_slots;
> -	DRM_DEBUG_KMS("vcpi slots avail=%d", topology_state->avail_slots);
> +		drm_dp_mst_get_port_malloc(port);
> +		vcpi->port = port;
> +		list_add(&vcpi->next, &topology_state->vcpis);
> +	}
> +	vcpi->vcpi = req_slots;
>  
> +	ret = req_slots;
> +out:
>  	drm_dp_mst_topology_put_port(port);
> -	return req_slots;
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
>  
> @@ -3064,31 +3119,57 @@ EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
>   * drm_dp_atomic_release_vcpi_slots() - Release allocated vcpi slots
>   * @state: global atomic state
>   * @mgr: MST topology manager for the port
> - * @slots: number of vcpi slots to release
> + * @port: The port to release the VCPI slots from
>   *
> - * RETURNS:
> - * 0 if @slots were added back to &drm_dp_mst_topology_state->avail_slots or
> - * negative error code
> + * Releases any VCPI slots that have been allocated to a port in the atomic
> + * state. Any atomic drivers which support MST must call this function in
> + * their &drm_connector_helper_funcs.atomic_check() callback when the
> + * connector will no longer have VCPI allocated (e.g. because it's CRTC was
> + * removed) when it had VCPI allocated in the previous atomic state.
> + *
> + * It is OK to call this even if @port has been removed from the system.
> + * Additionally, it is OK to call this function multiple times on the same
> + * @port as needed. It is not OK however, to call this function and
> + * drm_dp_atomic_find_vcpi_slots() on the same @port in a single atomic check
> + * phase.
> + *
> + * See also:
> + * drm_dp_atomic_find_vcpi_slots()
> + * drm_dp_mst_atomic_check()
> + *
> + * Returns:
> + * 0 if all slots for this port were added back to
> + * &drm_dp_mst_topology_state.avail_slots or negative error code
>   */
>  int drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
>  				     struct drm_dp_mst_topology_mgr *mgr,
> -				     int slots)
> +				     struct drm_dp_mst_port *port)
>  {
>  	struct drm_dp_mst_topology_state *topology_state;
> +	struct drm_dp_vcpi_allocation *pos;
> +	bool found = false;
>  
>  	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
>  	if (IS_ERR(topology_state))
>  		return PTR_ERR(topology_state);
>  
> -	/* We cannot rely on port->vcpi.num_slots to update
> -	 * topology_state->avail_slots as the port may not exist if the parent
> -	 * branch device was unplugged. This should be fixed by tracking
> -	 * per-port slot allocation in drm_dp_mst_topology_state instead of
> -	 * depending on the caller to tell us how many slots to release.
> -	 */
> -	topology_state->avail_slots += slots;
> -	DRM_DEBUG_KMS("vcpi slots released=%d, avail=%d\n",
> -			slots, topology_state->avail_slots);
> +	list_for_each_entry(pos, &topology_state->vcpis, next) {
> +		if (pos->port == port) {
> +			found = true;
> +			break;
> +		}
> +	}
> +	if (WARN_ON(!found)) {
> +		DRM_ERROR("no VCPI for [MST PORT:%p] found in mst state %p\n",
> +			  port, &topology_state->base);
> +		return -EINVAL;
> +	}
> +
> +	DRM_DEBUG_ATOMIC("[MST PORT:%p] VCPI %d -> 0\n", port, pos->vcpi);
> +	if (pos->vcpi) {
> +		drm_dp_mst_put_port_malloc(port);
> +		pos->vcpi = 0;
> +	}
>  
>  	return 0;
>  }
> @@ -3510,15 +3591,41 @@ static void drm_dp_destroy_connector_work(struct work_struct *work)
>  static struct drm_private_state *
>  drm_dp_mst_duplicate_state(struct drm_private_obj *obj)
>  {
> -	struct drm_dp_mst_topology_state *state;
> +	struct drm_dp_mst_topology_state *state, *old_state =
> +		to_dp_mst_topology_state(obj->state);
> +	struct drm_dp_vcpi_allocation *pos, *vcpi;
>  
> -	state = kmemdup(obj->state, sizeof(*state), GFP_KERNEL);
> +	state = kmemdup(old_state, sizeof(*state), GFP_KERNEL);
>  	if (!state)
>  		return NULL;
>  
>  	__drm_atomic_helper_private_obj_duplicate_state(obj, &state->base);
>  
> +	INIT_LIST_HEAD(&state->vcpis);
> +
> +	list_for_each_entry(pos, &old_state->vcpis, next) {
> +		/* Prune leftover freed VCPI allocations */
> +		if (!pos->vcpi)
> +			continue;
> +
> +		vcpi = kmemdup(pos, sizeof(*vcpi), GFP_KERNEL);
> +		if (!vcpi)
> +			goto fail;
> +
> +		drm_dp_mst_get_port_malloc(vcpi->port);
> +		list_add(&vcpi->next, &state->vcpis);
> +	}
> +
>  	return &state->base;
> +
> +fail:
> +	list_for_each_entry_safe(pos, vcpi, &state->vcpis, next) {
> +		drm_dp_mst_put_port_malloc(pos->port);
> +		kfree(pos);
> +	}
> +	kfree(state);
> +
> +	return NULL;
>  }
>  
>  static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
> @@ -3526,10 +3633,88 @@ static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
>  {
>  	struct drm_dp_mst_topology_state *mst_state =
>  		to_dp_mst_topology_state(state);
> +	struct drm_dp_vcpi_allocation *pos, *tmp;
> +
> +	list_for_each_entry_safe(pos, tmp, &mst_state->vcpis, next) {
> +		/* We only keep references to ports with non-zero VCPIs */
> +		if (pos->vcpi)
> +			drm_dp_mst_put_port_malloc(pos->port);
> +		kfree(pos);
> +	}
>  
>  	kfree(mst_state);
>  }
>  
> +static inline int
> +drm_dp_mst_atomic_check_topology_state(struct drm_dp_mst_topology_mgr *mgr,
> +				       struct drm_dp_mst_topology_state *mst_state)
> +{
> +	struct drm_dp_vcpi_allocation *vcpi;
> +	int avail_slots = 63;
> +
> +	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
> +		/* Releasing VCPI is always OK-even if the port is gone */
> +		if (!vcpi->vcpi) {
> +			DRM_DEBUG_ATOMIC("[MST PORT:%p] releases all VCPI slots\n",
> +					 vcpi->port);
> +			continue;
> +		}
> +
> +		DRM_DEBUG_ATOMIC("[MST PORT:%p] requires %d vcpi slots\n",
> +				 vcpi->port, vcpi->vcpi);
> +
> +		avail_slots -= vcpi->vcpi;
> +		if (avail_slots < 0) {
> +			DRM_DEBUG_ATOMIC("[MST PORT:%p] not enough VCPI slots in mst state %p (avail=%d)\n",
> +					 vcpi->port, mst_state,
> +					 avail_slots + vcpi->vcpi);
> +			return -ENOSPC;
> +		}
> +	}
> +	DRM_DEBUG_ATOMIC("[MST MGR:%p] mst state %p VCPI avail=%d used=%d\n",
> +			 mgr, mst_state, avail_slots,
> +			 63 - avail_slots);
> +
> +	return 0;
> +}
> +
> +/**
> + * drm_dp_mst_atomic_check - Check that the new state of an MST topology in an
> + * atomic update is valid
> + * @state: Pointer to the new &struct drm_dp_mst_topology_state
> + *
> + * Checks the given topology state for an atomic update to ensure that it's
> + * valid. This includes checking whether there's enough bandwidth to support
> + * the new VCPI allocations in the atomic update.
> + *
> + * Any atomic drivers supporting DP MST must make sure to call this after
> + * checking the rest of their state in their
> + * &drm_mode_config_funcs.atomic_check() callback.
> + *
> + * See also:
> + * drm_dp_atomic_find_vcpi_slots()
> + * drm_dp_atomic_release_vcpi_slots()
> + *
> + * Returns:
> + *
> + * 0 if the new state is valid, negative error code otherwise.
> + */
> +int drm_dp_mst_atomic_check(struct drm_atomic_state *state)
> +{
> +	struct drm_dp_mst_topology_mgr *mgr;
> +	struct drm_dp_mst_topology_state *mst_state;
> +	int i, ret = 0;
> +
> +	for_each_new_mst_mgr_in_state(state, mgr, mst_state, i) {
> +		ret = drm_dp_mst_atomic_check_topology_state(mgr, mst_state);
> +		if (ret)
> +			break;
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(drm_dp_mst_atomic_check);
> +
>  const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs = {
>  	.atomic_duplicate_state = drm_dp_mst_duplicate_state,
>  	.atomic_destroy_state = drm_dp_mst_destroy_state,
> @@ -3612,9 +3797,7 @@ int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr,
>  		return -ENOMEM;
>  
>  	mst_state->mgr = mgr;
> -
> -	/* max. time slots - one slot for MTP header */
> -	mst_state->avail_slots = 63;
> +	INIT_LIST_HEAD(&mst_state->vcpis);
>  
>  	drm_atomic_private_obj_init(dev, &mgr->base,
>  				    &mst_state->base,
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 696e6f5680df..d1595be4a880 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -12710,6 +12710,10 @@ static int intel_atomic_check(struct drm_device *dev,
>  				       "[modeset]" : "[fastset]");
>  	}
>  
> +	ret = drm_dp_mst_atomic_check(state);
> +	if (ret)
> +		return ret;
> +
>  	if (any_ms) {
>  		ret = intel_modeset_checks(state);
>  
> diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
> index 631fd1537252..c8e2215628e6 100644
> --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> @@ -41,8 +41,12 @@ static bool intel_dp_mst_compute_config(struct intel_encoder *encoder,
>  	struct drm_connector *connector = conn_state->connector;
>  	void *port = to_intel_connector(connector)->port;
>  	struct drm_atomic_state *state = pipe_config->base.state;
> +	struct drm_crtc *crtc = pipe_config->base.crtc;
> +	struct drm_crtc_state *old_crtc_state =
> +		drm_atomic_get_old_crtc_state(state, crtc);
>  	int bpp;
> -	int lane_count, slots = 0;
> +	int lane_count, slots =
> +		to_intel_crtc_state(old_crtc_state)->dp_m_n.tu;
>  	const struct drm_display_mode *adjusted_mode = &pipe_config->base.adjusted_mode;
>  	int mst_pbn;
>  	bool constant_n = drm_dp_has_quirk(&intel_dp->desc,
> @@ -107,35 +111,39 @@ static bool intel_dp_mst_compute_config(struct intel_encoder *encoder,
>  	return true;
>  }
>  
> -static int intel_dp_mst_atomic_check(struct drm_connector *connector,
> -		struct drm_connector_state *new_conn_state)
> +static int
> +intel_dp_mst_atomic_check(struct drm_connector *connector,
> +			  struct drm_connector_state *new_conn_state)
>  {
>  	struct drm_atomic_state *state = new_conn_state->state;
> -	struct drm_connector_state *old_conn_state;
> -	struct drm_crtc *old_crtc;
> +	struct drm_connector_state *old_conn_state =
> +		drm_atomic_get_old_connector_state(state, connector);
> +	struct intel_connector *intel_connector =
> +		to_intel_connector(connector);
> +	struct drm_crtc *new_crtc = new_conn_state->crtc;
>  	struct drm_crtc_state *crtc_state;
> -	int slots, ret = 0;
> +	struct drm_dp_mst_topology_mgr *mgr;
> +	int ret = 0;
>  
> -	old_conn_state = drm_atomic_get_old_connector_state(state, connector);
> -	old_crtc = old_conn_state->crtc;
> -	if (!old_crtc)
> -		return ret;
> -
> -	crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
> -	slots = to_intel_crtc_state(crtc_state)->dp_m_n.tu;
> -	if (drm_atomic_crtc_needs_modeset(crtc_state) && slots > 0) {
> -		struct drm_dp_mst_topology_mgr *mgr;
> -		struct drm_encoder *old_encoder;
> +	if (!old_conn_state->crtc)
> +		return 0;
>  
> -		old_encoder = old_conn_state->best_encoder;
> -		mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
> +	/* We only want to free VCPI if this state disables the CRTC on this
> +	 * connector
> +	 */
> +	if (new_crtc) {
> +		crtc_state = drm_atomic_get_new_crtc_state(state, new_crtc);
>  
> -		ret = drm_dp_atomic_release_vcpi_slots(state, mgr, slots);
> -		if (ret)
> -			DRM_DEBUG_KMS("failed releasing %d vcpi slots:%d\n", slots, ret);
> -		else
> -			to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
> +		if (!crtc_state ||
> +		    !drm_atomic_crtc_needs_modeset(crtc_state) ||
> +		    crtc_state->enable)
> +			return 0;
>  	}
> +
> +	mgr = &enc_to_mst(old_conn_state->best_encoder)->primary->dp.mst_mgr;
> +	ret = drm_dp_atomic_release_vcpi_slots(state, mgr,
> +					       intel_connector->port);
> +
>  	return ret;
>  }
>  
> diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
> index 581163c8d7d7..451d020f0137 100644
> --- a/include/drm/drm_dp_mst_helper.h
> +++ b/include/drm/drm_dp_mst_helper.h
> @@ -425,9 +425,15 @@ struct drm_dp_payload {
>  
>  #define to_dp_mst_topology_state(x) container_of(x, struct drm_dp_mst_topology_state, base)
>  
> +struct drm_dp_vcpi_allocation {
> +	struct drm_dp_mst_port *port;
> +	int vcpi;
> +	struct list_head next;
> +};
> +
>  struct drm_dp_mst_topology_state {
>  	struct drm_private_state base;
> -	int avail_slots;
> +	struct list_head vcpis;
>  	struct drm_dp_mst_topology_mgr *mgr;
>  };
>  
> @@ -638,14 +644,17 @@ void drm_dp_mst_topology_mgr_suspend(struct drm_dp_mst_topology_mgr *mgr);
>  int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr);
>  struct drm_dp_mst_topology_state *drm_atomic_get_mst_topology_state(struct drm_atomic_state *state,
>  								    struct drm_dp_mst_topology_mgr *mgr);
> -int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
> -				  struct drm_dp_mst_topology_mgr *mgr,
> -				  struct drm_dp_mst_port *port, int pbn);
> -int drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
> -				     struct drm_dp_mst_topology_mgr *mgr,
> -				     int slots);
> +int __must_check
> +drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
> +			      struct drm_dp_mst_topology_mgr *mgr,
> +			      struct drm_dp_mst_port *port, int pbn);
> +int __must_check
> +drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
> +				 struct drm_dp_mst_topology_mgr *mgr,
> +				 struct drm_dp_mst_port *port);
>  int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
>  				 struct drm_dp_mst_port *port, bool power_up);
> +int __must_check drm_dp_mst_atomic_check(struct drm_atomic_state *state);
>  
>  void drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port);
>  void drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port);
> -- 
> 2.20.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH v5 19/20] drm/dp_mst: Check payload count in drm_dp_mst_atomic_check()

[Daniel Vetter]

On Tue, Jan 08, 2019 at 07:35:16PM -0500, Lyude Paul wrote:
> It occurred to me that we never actually check this! So let's start
> doing that.
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: David Airlie <airlied@redhat.com>
> Cc: Jerry Zuo <Jerry.Zuo@amd.com>
> Cc: Harry Wentland <harry.wentland@amd.com>
> Cc: Juston Li <juston.li@intel.com>

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index fc778c6d487e..41cf814207bf 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -3650,7 +3650,7 @@ drm_dp_mst_atomic_check_topology_state(struct drm_dp_mst_topology_mgr *mgr,
>  				       struct drm_dp_mst_topology_state *mst_state)
>  {
>  	struct drm_dp_vcpi_allocation *vcpi;
> -	int avail_slots = 63;
> +	int avail_slots = 63, payload_count = 0;
>  
>  	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
>  		/* Releasing VCPI is always OK-even if the port is gone */
> @@ -3670,6 +3670,12 @@ drm_dp_mst_atomic_check_topology_state(struct drm_dp_mst_topology_mgr *mgr,
>  					 avail_slots + vcpi->vcpi);
>  			return -ENOSPC;
>  		}
> +
> +		if (++payload_count > mgr->max_payloads) {
> +			DRM_DEBUG_ATOMIC("[MST MGR:%p] state %p has too many payloads (max=%d)\n",
> +					 mgr, mst_state, mgr->max_payloads);
> +			return -EINVAL;
> +		}
>  	}
>  	DRM_DEBUG_ATOMIC("[MST MGR:%p] mst state %p VCPI avail=%d used=%d\n",
>  			 mgr, mst_state, avail_slots,
> -- 
> 2.20.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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