[PATCH v3 0/5] drm/dp_mst: Add some atomic state iterator macros

[PATCH v3 0/5] drm/dp_mst: Add some atomic state iterator macros

[Lyude Paul]

This patchset does some cleaning up of the atomic VCPI helpers for MST,
and converts nouveau over to using them. I would have included amdgpu in
this patch as well, but at the moment moving them over to the atomic
helpers is nontrivial.

Cc: Daniel Vetter <daniel@ffwll.ch>

Lyude Paul (5):
  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
  drm/dp_mst: Stop unsetting mstc->port, check connector registration

 drivers/gpu/drm/drm_dp_mst_topology.c   | 229 ++++++++++++++++++++----
 drivers/gpu/drm/i915/intel_display.c    |   4 +
 drivers/gpu/drm/i915/intel_dp_mst.c     |  31 ++--
 drivers/gpu/drm/nouveau/dispnv50/disp.c |  65 +++++--
 include/drm/drm_dp_mst_helper.h         | 100 ++++++++++-
 5 files changed, 359 insertions(+), 70 deletions(-)

-- 
2.19.1

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[PATCH v3 1/5] drm/dp_mst: Add some atomic state iterator macros

[Lyude Paul]

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 include/drm/drm_dp_mst_helper.h | 77 +++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)

diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 59f005b419cf..3faceb66f5cb 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -628,4 +628,81 @@ 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);
 
+extern const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs;
+
+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
-- 
2.19.1

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[PATCH v3 2/5] 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 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>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 222 ++++++++++++++++++++++----
 drivers/gpu/drm/i915/intel_display.c  |   4 +
 drivers/gpu/drm/i915/intel_dp_mst.c   |  31 ++--
 include/drm/drm_dp_mst_helper.h       |  23 ++-
 4 files changed, 225 insertions(+), 55 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 8c3cfac437f4..74823afb262e 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2614,21 +2614,34 @@ 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. The allocations are not checked
+ * against the bandwidth restraints of @mgr until the driver calls
+ * drm_dp_mst_atomic_check().
+ *
+ * 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))
@@ -2637,20 +2650,41 @@ int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
 	port = drm_dp_get_validated_port_ref(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_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;
+			break;
+		}
 	}
+	if (!vcpi)
+		prev_slots = 0;
+
+	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
 
-	topology_state->avail_slots -= req_slots;
-	DRM_DEBUG_KMS("vcpi slots avail=%d", topology_state->avail_slots);
+	DRM_DEBUG_KMS("[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;
+		}
+
+		vcpi->port = port;
+		list_add(&vcpi->next, &topology_state->vcpis);
+	}
+	vcpi->vcpi = req_slots;
+
+	ret = req_slots;
+out:
 	drm_dp_put_port(port);
-	return req_slots;
+	return ret;
 }
 EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
 
@@ -2658,32 +2692,50 @@ 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).
+ *
+ * It is OK to call this even if @port has been removed from the system, in
+ * which case it will just amount to a no-op.
+ *
+ * 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 *tmp, *pos;
 
 	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_safe(pos, tmp, &topology_state->vcpis, next) {
+		if (pos->port == port) {
+			list_del(&pos->next);
+			DRM_DEBUG_KMS("[MST PORT:%p] vcpi %d -> 0\n",
+				      port, pos->vcpi);
 
+			kfree(pos);
+			return 0;
+		}
+	}
+
+	/* If no allocation was found, all that means is that the port was
+	 * destroyed since the last atomic commit. That's OK!
+	 */
 	return 0;
 }
 EXPORT_SYMBOL(drm_dp_atomic_release_vcpi_slots);
@@ -3112,15 +3164,34 @@ 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) {
+		vcpi = kmemdup(pos, sizeof(*vcpi), GFP_KERNEL);
+		if (!vcpi)
+			goto fail_alloc;
+
+		list_add(&vcpi->next, &state->vcpis);
+	}
+
 	return &state->base;
+
+fail_alloc:
+	list_for_each_entry_safe(pos, vcpi, &state->vcpis, next)
+		kfree(pos);
+	kfree(state);
+
+	return NULL;
 }
 
 static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
@@ -3128,14 +3199,99 @@ 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)
+		kfree(pos);
 
 	kfree(mst_state);
 }
 
-static const struct drm_private_state_funcs mst_state_funcs = {
+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;
+	struct drm_dp_mst_port *port;
+	int avail_slots = 63, ret;
+
+	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
+		/* Ports that no longer exist shouldn't be counted towards the
+		 * bandwidth requirements for the state, so skip them
+		 */
+		port = drm_dp_get_validated_port_ref(mgr, vcpi->port);
+		if (!port) {
+			DRM_DEBUG_ATOMIC("[MST PORT:%p] is stale, skipping checks\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);
+			ret = -ENOSPC;
+			goto port_fail;
+		}
+
+		drm_dp_put_port(port);
+	}
+	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;
+port_fail:
+	drm_dp_put_port(port);
+	return ret;
+}
+
+/**
+ * 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,
 };
+EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);
 
 /**
  * drm_atomic_get_mst_topology_state: get MST topology state
@@ -3213,13 +3369,11 @@ 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(&mgr->base,
 				    &mst_state->base,
-				    &mst_state_funcs);
+				    &drm_dp_mst_topology_state_funcs);
 
 	return 0;
 }
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index bbf8ca21a7a2..8749cf61a6ac 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12553,6 +12553,10 @@ 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 8b71d64ebd9d..aaf904738b78 100644
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -114,28 +114,31 @@ static int intel_dp_mst_atomic_check(struct drm_connector *connector,
 	struct drm_connector_state *old_conn_state;
 	struct drm_crtc *old_crtc;
 	struct drm_crtc_state *crtc_state;
-	int slots, ret = 0;
+	struct intel_connector *intel_connector =
+		to_intel_connector(connector);
+	struct drm_dp_mst_topology_mgr *mgr =
+		&intel_connector->mst_port->mst_mgr;
+	struct drm_dp_mst_port *port = intel_connector->port;
+	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;
+	/* Free VCPI, since compute_config() won't be run */
+	if (!new_conn_state->crtc) {
+		crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
 
-		old_encoder = old_conn_state->best_encoder;
-		mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
-
-		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;
+		ret = drm_dp_atomic_release_vcpi_slots(state, mgr, port);
+		if (ret) {
+			DRM_DEBUG_KMS("failed releasing vcpi slots: %d\n",
+				      ret);
+			return ret;
+		}
+		to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
 	}
+
 	return ret;
 }
 
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 3faceb66f5cb..08b67948b8f9 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -406,9 +406,15 @@ 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;
 };
 
@@ -619,14 +625,17 @@ 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);
 
 extern const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs;
 
-- 
2.19.1

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[PATCH v3 3/5] 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>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 74823afb262e..8ef0c5f5c7cf 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3213,7 +3213,7 @@ drm_dp_mst_atomic_check_topology_state(struct drm_dp_mst_topology_mgr *mgr,
 {
 	struct drm_dp_vcpi_allocation *vcpi;
 	struct drm_dp_mst_port *port;
-	int avail_slots = 63, ret;
+	int avail_slots = 63, payload_count = 0, ret;
 
 	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
 		/* Ports that no longer exist shouldn't be counted towards the
@@ -3238,6 +3238,13 @@ drm_dp_mst_atomic_check_topology_state(struct drm_dp_mst_topology_mgr *mgr,
 			goto port_fail;
 		}
 
+		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);
+			ret = -EINVAL;
+			goto port_fail;
+		}
+
 		drm_dp_put_port(port);
 	}
 	DRM_DEBUG_ATOMIC("[MST MGR:%p] mst_state %p vcpi avail=%d used=%d\n",
-- 
2.19.1

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[PATCH v3 4/5] 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.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c | 50 +++++++++++++++++++++----
 1 file changed, 43 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 6cbbae3f438b..0469ef9e1a54 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -747,16 +747,22 @@ 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);
-
-	slots = drm_dp_find_vcpi_slots(&mstm->mgr, mstc->pbn);
-	if (slots < 0)
-		return slots;
+	mstc->pbn = drm_dp_calc_pbn_mode(crtc_state->adjusted_mode.clock,
+					 bpp);
+	/* Zombies don't need VCPI */
+	if (!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);
@@ -920,12 +926,38 @@ 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;
+	struct drm_crtc *old_crtc;
+
+	old_conn_state = drm_atomic_get_old_connector_state(state, connector);
+	old_crtc = old_conn_state->crtc;
+
+	/* We only need to release VCPI here if we're going from having a CRTC
+	 * on this connector, to not having one
+	 */
+	if (!old_crtc || new_conn_state->crtc)
+		return 0;
+
+	/* Release the previous VCPI allocation since the encoder's
+	 * atomic_check() won't be called
+	 */
+	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
@@ -2109,6 +2141,10 @@ 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;
 }
 
-- 
2.19.1

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[PATCH v3 5/5] drm/dp_mst: Stop unsetting mstc->port, check connector registration

[Lyude Paul]

Same thing we did in i915, but for nouveau now.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 0469ef9e1a54..ff04a56b5949 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -698,8 +698,10 @@ nv50_msto_cleanup(struct nv50_msto *msto)
 	struct nv50_mstm *mstm = mstc->mstm;
 
 	NV_ATOMIC(drm, "%s: msto cleanup\n", msto->encoder.name);
-	if (mstc->port && mstc->port->vcpi.vcpi > 0 && !nv50_msto_payload(msto))
+	if (!drm_connector_is_unregistered(&mstc->connector) &&
+	    mstc->port->vcpi.vcpi > 0 && !nv50_msto_payload(msto))
 		drm_dp_mst_deallocate_vcpi(&mstm->mgr, mstc->port);
+
 	if (msto->disabled) {
 		msto->mstc = NULL;
 		msto->head = NULL;
@@ -725,7 +727,8 @@ 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 (!drm_connector_is_unregistered(&mstc->connector) &&
+	    mstc->port->vcpi.vcpi > 0) {
 		struct drm_dp_payload *payload = nv50_msto_payload(msto);
 		if (payload) {
 			args.vcpi.start_slot = payload->start_slot;
@@ -828,7 +831,7 @@ nv50_msto_disable(struct drm_encoder *encoder)
 	struct nv50_mstc *mstc = msto->mstc;
 	struct nv50_mstm *mstm = mstc->mstm;
 
-	if (mstc->port)
+	if (!drm_connector_is_unregistered(&mstc->connector))
 		drm_dp_mst_reset_vcpi_slots(&mstm->mgr, mstc->port);
 
 	mstm->outp->update(mstm->outp, msto->head->base.index, NULL, 0, 0);
@@ -967,7 +970,7 @@ 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(&mstc->connector))
 		return connector_status_disconnected;
 
 	ret = pm_runtime_get_sync(connector->dev->dev);
@@ -1105,10 +1108,6 @@ 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);
-	mstc->port = NULL;
-	drm_modeset_unlock(&drm->dev->mode_config.connection_mutex);
-
 	drm_connector_put(&mstc->connector);
 }
 
-- 
2.19.1

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✗ Fi.CI.CHECKPATCH: warning for drm/dp_mst: Add some atomic state iterator macros

[Patchwork]

== Series Details ==

Series: drm/dp_mst: Add some atomic state iterator macros
URL   : https://patchwork.freedesktop.org/series/52130/
State : warning

== Summary ==

$ dim checkpatch origin/drm-tip
f9a06ea3b5c0 drm/dp_mst: Add some atomic state iterator macros
-:7: WARNING:COMMIT_MESSAGE: Missing commit description - Add an appropriate one

-:55: CHECK:MACRO_ARG_REUSE: Macro argument reuse '__state' - possible side-effects?
#55: FILE: include/drm/drm_dp_mst_helper.h:669:
+#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)))

-:55: CHECK:MACRO_ARG_REUSE: Macro argument reuse '__i' - possible side-effects?
#55: FILE: include/drm/drm_dp_mst_helper.h:669:
+#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)))

-:57: WARNING:LONG_LINE: line over 100 characters
#57: FILE: include/drm/drm_dp_mst_helper.h:671:
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), &(old_state), &(new_state), (__i)))

-:72: CHECK:MACRO_ARG_REUSE: Macro argument reuse '__state' - possible side-effects?
#72: FILE: include/drm/drm_dp_mst_helper.h:686:
+#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)))

-:72: CHECK:MACRO_ARG_REUSE: Macro argument reuse '__i' - possible side-effects?
#72: FILE: include/drm/drm_dp_mst_helper.h:686:
+#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)))

-:74: WARNING:LONG_LINE: line over 100 characters
#74: FILE: include/drm/drm_dp_mst_helper.h:688:
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), &(old_state), NULL, (__i)))

-:90: CHECK:MACRO_ARG_REUSE: Macro argument reuse '__state' - possible side-effects?
#90: FILE: include/drm/drm_dp_mst_helper.h:704:
+#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)))

-:90: CHECK:MACRO_ARG_REUSE: Macro argument reuse '__i' - possible side-effects?
#90: FILE: include/drm/drm_dp_mst_helper.h:704:
+#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)))

-:92: WARNING:LONG_LINE: line over 100 characters
#92: FILE: include/drm/drm_dp_mst_helper.h:706:
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), NULL, &(new_state), (__i)))

total: 0 errors, 4 warnings, 6 checks, 81 lines checked
2f6f91409c1d drm/dp_mst: Start tracking per-port VCPI allocations
3595cf182bc3 drm/dp_mst: Check payload count in drm_dp_mst_atomic_check()
65ad86529a15 drm/nouveau: Use atomic VCPI helpers for MST
b58c9476ea09 drm/dp_mst: Stop unsetting mstc->port, check connector registration

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✗ Fi.CI.SPARSE: warning for drm/dp_mst: Add some atomic state iterator macros

[Patchwork]

== Series Details ==

Series: drm/dp_mst: Add some atomic state iterator macros
URL   : https://patchwork.freedesktop.org/series/52130/
State : warning

== Summary ==

$ dim sparse origin/drm-tip
Sparse version: v0.5.2
Commit: drm/dp_mst: Add some atomic state iterator macros
Okay!

Commit: drm/dp_mst: Start tracking per-port VCPI allocations
+./include/linux/slab.h:332:43: warning: dubious: x & !y

Commit: drm/dp_mst: Check payload count in drm_dp_mst_atomic_check()
Okay!

Commit: drm/nouveau: Use atomic VCPI helpers for MST
Okay!

Commit: drm/dp_mst: Stop unsetting mstc->port, check connector registration
Okay!

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✓ Fi.CI.BAT: success for drm/dp_mst: Add some atomic state iterator macros

[Patchwork]

== Series Details ==

Series: drm/dp_mst: Add some atomic state iterator macros
URL   : https://patchwork.freedesktop.org/series/52130/
State : success

== Summary ==

= CI Bug Log - changes from CI_DRM_5097 -> Patchwork_10749 =

== Summary - SUCCESS ==

  No regressions found.

  External URL: https://patchwork.freedesktop.org/api/1.0/series/52130/revisions/1/mbox/

== Known issues ==

  Here are the changes found in Patchwork_10749 that come from known issues:

  === IGT changes ===

    ==== Issues hit ====

    igt@drv_selftest@live_coherency:
      fi-gdg-551:         PASS -> DMESG-FAIL (fdo#107164)

    
    ==== Possible fixes ====

    igt@drv_selftest@live_hangcheck:
      fi-cfl-8109u:       INCOMPLETE (fdo#106070) -> PASS

    igt@gem_exec_suspend@basic-s3:
      fi-blb-e6850:       INCOMPLETE (fdo#107718) -> PASS

    igt@kms_pipe_crc_basic@nonblocking-crc-pipe-a:
      fi-byt-clapper:     FAIL (fdo#107362) -> PASS

    igt@kms_pipe_crc_basic@read-crc-pipe-a-frame-sequence:
      fi-byt-clapper:     FAIL (fdo#103191, fdo#107362) -> PASS

    igt@kms_pipe_crc_basic@suspend-read-crc-pipe-b:
      fi-cfl-8109u:       DMESG-WARN (fdo#107345) -> PASS +2

    
  fdo#103191 https://bugs.freedesktop.org/show_bug.cgi?id=103191
  fdo#106070 https://bugs.freedesktop.org/show_bug.cgi?id=106070
  fdo#107164 https://bugs.freedesktop.org/show_bug.cgi?id=107164
  fdo#107345 https://bugs.freedesktop.org/show_bug.cgi?id=107345
  fdo#107362 https://bugs.freedesktop.org/show_bug.cgi?id=107362
  fdo#107718 https://bugs.freedesktop.org/show_bug.cgi?id=107718


== Participating hosts (52 -> 46) ==

  Missing    (6): fi-kbl-soraka fi-ilk-m540 fi-hsw-4200u fi-byt-squawks fi-bsw-cyan fi-ctg-p8600 


== Build changes ==

    * Linux: CI_DRM_5097 -> Patchwork_10749

  CI_DRM_5097: c20dfc4f015dfd41246beb7d72338aa50543a5ef @ git://anongit.freedesktop.org/gfx-ci/linux
  IGT_4711: cc41f4c921e56c62c85ec5349c47022ae9b5f008 @ git://anongit.freedesktop.org/xorg/app/intel-gpu-tools
  Patchwork_10749: b58c9476ea09620366de5a2ba7ecbcd01a5a8962 @ git://anongit.freedesktop.org/gfx-ci/linux


== Linux commits ==

b58c9476ea09 drm/dp_mst: Stop unsetting mstc->port, check connector registration
65ad86529a15 drm/nouveau: Use atomic VCPI helpers for MST
3595cf182bc3 drm/dp_mst: Check payload count in drm_dp_mst_atomic_check()
2f6f91409c1d drm/dp_mst: Start tracking per-port VCPI allocations
f9a06ea3b5c0 drm/dp_mst: Add some atomic state iterator macros

== Logs ==

For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_10749/issues.html
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Re: [PATCH v3 2/5] drm/dp_mst: Start tracking per-port VCPI allocations

[Daniel Vetter]

On Tue, Nov 06, 2018 at 08:21:14PM -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 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>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 222 ++++++++++++++++++++++----
>  drivers/gpu/drm/i915/intel_display.c  |   4 +
>  drivers/gpu/drm/i915/intel_dp_mst.c   |  31 ++--
>  include/drm/drm_dp_mst_helper.h       |  23 ++-
>  4 files changed, 225 insertions(+), 55 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 8c3cfac437f4..74823afb262e 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -2614,21 +2614,34 @@ 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. The allocations are not checked
> + * against the bandwidth restraints of @mgr until the driver calls
> + * drm_dp_mst_atomic_check().
> + *
> + * 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))
> @@ -2637,20 +2650,41 @@ int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
>  	port = drm_dp_get_validated_port_ref(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_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;
> +			break;
> +		}
>  	}
> +	if (!vcpi)
> +		prev_slots = 0;
> +
> +	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
>  
> -	topology_state->avail_slots -= req_slots;
> -	DRM_DEBUG_KMS("vcpi slots avail=%d", topology_state->avail_slots);
> +	DRM_DEBUG_KMS("[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;
> +		}
> +
> +		vcpi->port = port;
> +		list_add(&vcpi->next, &topology_state->vcpis);
> +	}
> +	vcpi->vcpi = req_slots;
> +
> +	ret = req_slots;
> +out:
>  	drm_dp_put_port(port);
> -	return req_slots;
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
>  
> @@ -2658,32 +2692,50 @@ 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).
> + *
> + * It is OK to call this even if @port has been removed from the system, in
> + * which case it will just amount to a no-op.
> + *
> + * 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 *tmp, *pos;
>  
>  	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_safe(pos, tmp, &topology_state->vcpis, next) {
> +		if (pos->port == port) {
> +			list_del(&pos->next);
> +			DRM_DEBUG_KMS("[MST PORT:%p] vcpi %d -> 0\n",
> +				      port, pos->vcpi);
>  
> +			kfree(pos);
> +			return 0;
> +		}
> +	}
> +
> +	/* If no allocation was found, all that means is that the port was
> +	 * destroyed since the last atomic commit. That's OK!
> +	 */

This case here has me a bit worried. I thought with your changes we'll
always have the port pointer still around, to be able to clean things up
properly. If this is not the case then we'd potentially leak the vcpi
allocation for an unplugged port.

Otoh if the driver releases the allocation for a port twice it's probably
mixed up it's own book-keeping. We should WARN about that case.

This is kinda fallout from your change to not prune allocations on
duplicate, and I think will further clean up how this is handled.

So with the comment removed and replaced by a WARNING(1,"no vcpi
allocation found for port %p\n", port) or something like that this should
be solid.


>  	return 0;
>  }
>  EXPORT_SYMBOL(drm_dp_atomic_release_vcpi_slots);
> @@ -3112,15 +3164,34 @@ 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) {
> +		vcpi = kmemdup(pos, sizeof(*vcpi), GFP_KERNEL);
> +		if (!vcpi)
> +			goto fail_alloc;
> +
> +		list_add(&vcpi->next, &state->vcpis);
> +	}
> +
>  	return &state->base;
> +
> +fail_alloc:
> +	list_for_each_entry_safe(pos, vcpi, &state->vcpis, next)
> +		kfree(pos);
> +	kfree(state);
> +
> +	return NULL;
>  }
>  
>  static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
> @@ -3128,14 +3199,99 @@ 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)
> +		kfree(pos);
>  
>  	kfree(mst_state);
>  }
>  
> -static const struct drm_private_state_funcs mst_state_funcs = {
> +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;
> +	struct drm_dp_mst_port *port;
> +	int avail_slots = 63, ret;
> +
> +	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
> +		/* Ports that no longer exist shouldn't be counted towards the
> +		 * bandwidth requirements for the state, so skip them
> +		 */

Scenario:
- 2 mst sinks on a single host side port.
- 1st connector is active, 2nd connector is off.
- 1st connector is hot-unplugged, but userspace hasn't realized this yet,
  so not yet come around to do the disabling modeset.
- At the same time userspace decides to enable the 2nd output, which
  forces a modeset and pulls the topology state in.
- This function here decides to only look at the vcpi allocation for the
  2nd connector because the first one is gone already.
- Unfortunately lighting up both connectors at the same time isn't
  possible, because too many vcpi. But since userspace didn't ask for a
  modeset on the now unplugged first connector.
-> Modeset goes boom because we enable too many vcpi.

But with the change in how we release vcpi allocations there's no need to
ignore disconnected stuff here, and we should be able to check vcpi limits
by just checking all of them.

I didn't see anything else serious, so with the above two things resolved
this has my Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

One bikeshed below, because I need to prove I scrolled to the end :-)

> +		port = drm_dp_get_validated_port_ref(mgr, vcpi->port);
> +		if (!port) {
> +			DRM_DEBUG_ATOMIC("[MST PORT:%p] is stale, skipping checks\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);
> +			ret = -ENOSPC;
> +			goto port_fail;
> +		}
> +
> +		drm_dp_put_port(port);
> +	}
> +	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;
> +port_fail:
> +	drm_dp_put_port(port);
> +	return ret;
> +}
> +
> +/**
> + * 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,
>  };
> +EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);
>  
>  /**
>   * drm_atomic_get_mst_topology_state: get MST topology state
> @@ -3213,13 +3369,11 @@ 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(&mgr->base,
>  				    &mst_state->base,
> -				    &mst_state_funcs);
> +				    &drm_dp_mst_topology_state_funcs);
>  
>  	return 0;
>  }
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index bbf8ca21a7a2..8749cf61a6ac 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -12553,6 +12553,10 @@ static int intel_atomic_check(struct drm_device *dev,
>  				       "[modeset]" : "[fastset]");
>  	}
>  
> +	ret = drm_dp_mst_atomic_check(state);
> +	if (ret)
> +		return ret;

Complete bikeshed, so feel free to ignore: I'd stuff this into
intel_modeset_checks(). Feel free to ignore.

Cheers, Daniel

> +
>  	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 8b71d64ebd9d..aaf904738b78 100644
> --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> @@ -114,28 +114,31 @@ static int intel_dp_mst_atomic_check(struct drm_connector *connector,
>  	struct drm_connector_state *old_conn_state;
>  	struct drm_crtc *old_crtc;
>  	struct drm_crtc_state *crtc_state;
> -	int slots, ret = 0;
> +	struct intel_connector *intel_connector =
> +		to_intel_connector(connector);
> +	struct drm_dp_mst_topology_mgr *mgr =
> +		&intel_connector->mst_port->mst_mgr;
> +	struct drm_dp_mst_port *port = intel_connector->port;
> +	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;
> +	/* Free VCPI, since compute_config() won't be run */
> +	if (!new_conn_state->crtc) {
> +		crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
>  
> -		old_encoder = old_conn_state->best_encoder;
> -		mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
> -
> -		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;
> +		ret = drm_dp_atomic_release_vcpi_slots(state, mgr, port);
> +		if (ret) {
> +			DRM_DEBUG_KMS("failed releasing vcpi slots: %d\n",
> +				      ret);
> +			return ret;
> +		}
> +		to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
>  	}
> +
>  	return ret;
>  }
>  
> diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
> index 3faceb66f5cb..08b67948b8f9 100644
> --- a/include/drm/drm_dp_mst_helper.h
> +++ b/include/drm/drm_dp_mst_helper.h
> @@ -406,9 +406,15 @@ 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;
>  };
>  
> @@ -619,14 +625,17 @@ 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);
>  
>  extern const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs;
>  
> -- 
> 2.19.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH v3 2/5] drm/dp_mst: Start tracking per-port VCPI allocations

[Lyude Paul]

On Wed, 2018-11-07 at 21:59 +0100, Daniel Vetter wrote:
> On Tue, Nov 06, 2018 at 08:21:14PM -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 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>
> > ---
> >  drivers/gpu/drm/drm_dp_mst_topology.c | 222 ++++++++++++++++++++++----
> >  drivers/gpu/drm/i915/intel_display.c  |   4 +
> >  drivers/gpu/drm/i915/intel_dp_mst.c   |  31 ++--
> >  include/drm/drm_dp_mst_helper.h       |  23 ++-
> >  4 files changed, 225 insertions(+), 55 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > index 8c3cfac437f4..74823afb262e 100644
> > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > @@ -2614,21 +2614,34 @@ 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. The allocations are not
> > checked
> > + * against the bandwidth restraints of @mgr until the driver calls
> > + * drm_dp_mst_atomic_check().
> > + *
> > + * 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))
> > @@ -2637,20 +2650,41 @@ int drm_dp_atomic_find_vcpi_slots(struct
> > drm_atomic_state *state,
> >  	port = drm_dp_get_validated_port_ref(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_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;
> > +			break;
> > +		}
> >  	}
> > +	if (!vcpi)
> > +		prev_slots = 0;
> > +
> > +	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
> >  
> > -	topology_state->avail_slots -= req_slots;
> > -	DRM_DEBUG_KMS("vcpi slots avail=%d", topology_state->avail_slots);
> > +	DRM_DEBUG_KMS("[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;
> > +		}
> > +
> > +		vcpi->port = port;
> > +		list_add(&vcpi->next, &topology_state->vcpis);
> > +	}
> > +	vcpi->vcpi = req_slots;
> > +
> > +	ret = req_slots;
> > +out:
> >  	drm_dp_put_port(port);
> > -	return req_slots;
> > +	return ret;
> >  }
> >  EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
> >  
> > @@ -2658,32 +2692,50 @@ 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).
> > + *
> > + * It is OK to call this even if @port has been removed from the system,
> > in
> > + * which case it will just amount to a no-op.
> > + *
> > + * 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 *tmp, *pos;
> >  
> >  	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_safe(pos, tmp, &topology_state->vcpis, next) {
> > +		if (pos->port == port) {
> > +			list_del(&pos->next);
> > +			DRM_DEBUG_KMS("[MST PORT:%p] vcpi %d -> 0\n",
> > +				      port, pos->vcpi);
> >  
> > +			kfree(pos);
> > +			return 0;
> > +		}
> > +	}
> > +
> > +	/* If no allocation was found, all that means is that the port was
> > +	 * destroyed since the last atomic commit. That's OK!
> > +	 */
> 
> This case here has me a bit worried. I thought with your changes we'll
> always have the port pointer still around, to be able to clean things up
> properly. If this is not the case then we'd potentially leak the vcpi
> allocation for an unplugged port.
> 
> Otoh if the driver releases the allocation for a port twice it's probably
> mixed up it's own book-keeping. We should WARN about that case.
> 
> This is kinda fallout from your change to not prune allocations on
> duplicate, and I think will further clean up how this is handled.
> 
> So with the comment removed and replaced by a WARNING(1,"no vcpi
> allocation found for port %p\n", port) or something like that this should
> be solid.

Hm; that comment is leftover from the fallout of moving the port verification
logic out of the state duplicate functions, but I don't think this would
nessecarily be a bookkeeping error. If we're going to support fallback
link retraining, we'll need to make sure that every driver's
drm_connector->atomic_check() function is idempotent so that if the
atomic helpers have to pull in more CRTCs to perform modesets on then
userspace originally added, the second check on the DRM connector
doesn't cause any issues. Remember: if we're trying to retrain an MST
topology at a lower link rate then before, that means changing the PBN
divisor which in turn means that the only valid actions that can be
taken are recalculating every active VCPI allocation at once in order to
prevent state inconsistencies, or disabling all of the displays (since
going from >0 VCPI to 0 VCPI should always be safe).

We /could/ just leave this up to the driver to do the bookkeeping on
this, but that seems rather redundant. We could add extra bookkeeping in
the atomic check though so that instead of just deleting the structs for
each VCPI allocation when they go to 0, we instead just set them to 0
then free them somewhere else.

> 
> 
> >  	return 0;
> >  }
> >  EXPORT_SYMBOL(drm_dp_atomic_release_vcpi_slots);
> > @@ -3112,15 +3164,34 @@ 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) {
> > +		vcpi = kmemdup(pos, sizeof(*vcpi), GFP_KERNEL);
> > +		if (!vcpi)
> > +			goto fail_alloc;
> > +
> > +		list_add(&vcpi->next, &state->vcpis);
> > +	}
> > +
> >  	return &state->base;
> > +
> > +fail_alloc:
> > +	list_for_each_entry_safe(pos, vcpi, &state->vcpis, next)
> > +		kfree(pos);
> > +	kfree(state);
> > +
> > +	return NULL;
> >  }
> >  
> >  static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
> > @@ -3128,14 +3199,99 @@ 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)
> > +		kfree(pos);
> >  
> >  	kfree(mst_state);
> >  }
> >  
> > -static const struct drm_private_state_funcs mst_state_funcs = {
> > +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;
> > +	struct drm_dp_mst_port *port;
> > +	int avail_slots = 63, ret;
> > +
> > +	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
> > +		/* Ports that no longer exist shouldn't be counted towards the
> > +		 * bandwidth requirements for the state, so skip them
> > +		 */
> 
> Scenario:
> - 2 mst sinks on a single host side port.
> - 1st connector is active, 2nd connector is off.
> - 1st connector is hot-unplugged, but userspace hasn't realized this yet,
>   so not yet come around to do the disabling modeset.
> - At the same time userspace decides to enable the 2nd output, which
>   forces a modeset and pulls the topology state in.
> - This function here decides to only look at the vcpi allocation for the
>   2nd connector because the first one is gone already.
> - Unfortunately lighting up both connectors at the same time isn't
>   possible, because too many vcpi. But since userspace didn't ask for a
>   modeset on the now unplugged first connector.
> -> Modeset goes boom because we enable too many vcpi.
> 
> But with the change in how we release vcpi allocations there's no need to
> ignore disconnected stuff here, and we should be able to check vcpi limits
> by just checking all of them.
> 
> I didn't see anything else serious, so with the above two things resolved
> this has my Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> One bikeshed below, because I need to prove I scrolled to the end :-)
> 
> > +		port = drm_dp_get_validated_port_ref(mgr, vcpi->port);
> > +		if (!port) {
> > +			DRM_DEBUG_ATOMIC("[MST PORT:%p] is stale, skipping
> > checks\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);
> > +			ret = -ENOSPC;
> > +			goto port_fail;
> > +		}
> > +
> > +		drm_dp_put_port(port);
> > +	}
> > +	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;
> > +port_fail:
> > +	drm_dp_put_port(port);
> > +	return ret;
> > +}
> > +
> > +/**
> > + * 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,
> >  };
> > +EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);
> >  
> >  /**
> >   * drm_atomic_get_mst_topology_state: get MST topology state
> > @@ -3213,13 +3369,11 @@ 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(&mgr->base,
> >  				    &mst_state->base,
> > -				    &mst_state_funcs);
> > +				    &drm_dp_mst_topology_state_funcs);
> >  
> >  	return 0;
> >  }
> > diff --git a/drivers/gpu/drm/i915/intel_display.c
> > b/drivers/gpu/drm/i915/intel_display.c
> > index bbf8ca21a7a2..8749cf61a6ac 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -12553,6 +12553,10 @@ static int intel_atomic_check(struct drm_device
> > *dev,
> >  				       "[modeset]" : "[fastset]");
> >  	}
> >  
> > +	ret = drm_dp_mst_atomic_check(state);
> > +	if (ret)
> > +		return ret;
> 
> Complete bikeshed, so feel free to ignore: I'd stuff this into
> intel_modeset_checks(). Feel free to ignore.
> 
> Cheers, Daniel
> 
> > +
> >  	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 8b71d64ebd9d..aaf904738b78 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> > @@ -114,28 +114,31 @@ static int intel_dp_mst_atomic_check(struct
> > drm_connector *connector,
> >  	struct drm_connector_state *old_conn_state;
> >  	struct drm_crtc *old_crtc;
> >  	struct drm_crtc_state *crtc_state;
> > -	int slots, ret = 0;
> > +	struct intel_connector *intel_connector =
> > +		to_intel_connector(connector);
> > +	struct drm_dp_mst_topology_mgr *mgr =
> > +		&intel_connector->mst_port->mst_mgr;
> > +	struct drm_dp_mst_port *port = intel_connector->port;
> > +	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;
> > +	/* Free VCPI, since compute_config() won't be run */
> > +	if (!new_conn_state->crtc) {
> > +		crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
> >  
> > -		old_encoder = old_conn_state->best_encoder;
> > -		mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
> > -
> > -		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;
> > +		ret = drm_dp_atomic_release_vcpi_slots(state, mgr, port);
> > +		if (ret) {
> > +			DRM_DEBUG_KMS("failed releasing vcpi slots: %d\n",
> > +				      ret);
> > +			return ret;
> > +		}
> > +		to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
> >  	}
> > +
> >  	return ret;
> >  }
> >  
> > diff --git a/include/drm/drm_dp_mst_helper.h
> > b/include/drm/drm_dp_mst_helper.h
> > index 3faceb66f5cb..08b67948b8f9 100644
> > --- a/include/drm/drm_dp_mst_helper.h
> > +++ b/include/drm/drm_dp_mst_helper.h
> > @@ -406,9 +406,15 @@ 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;
> >  };
> >  
> > @@ -619,14 +625,17 @@ 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);
> >  
> >  extern const struct drm_private_state_funcs
> > drm_dp_mst_topology_state_funcs;
> >  
> > -- 
> > 2.19.1
> > 
-- 
Cheers,
	Lyude Paul

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Re: [PATCH v3 2/5] drm/dp_mst: Start tracking per-port VCPI allocations

[Lyude Paul]

On Wed, 2018-11-07 at 16:23 -0500, Lyude Paul wrote:
> On Wed, 2018-11-07 at 21:59 +0100, Daniel Vetter wrote:
> > On Tue, Nov 06, 2018 at 08:21:14PM -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 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>
> > > ---
> > >  drivers/gpu/drm/drm_dp_mst_topology.c | 222 ++++++++++++++++++++++----
> > >  drivers/gpu/drm/i915/intel_display.c  |   4 +
> > >  drivers/gpu/drm/i915/intel_dp_mst.c   |  31 ++--
> > >  include/drm/drm_dp_mst_helper.h       |  23 ++-
> > >  4 files changed, 225 insertions(+), 55 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > index 8c3cfac437f4..74823afb262e 100644
> > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > @@ -2614,21 +2614,34 @@ 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. The allocations are not
> > > checked
> > > + * against the bandwidth restraints of @mgr until the driver calls
> > > + * drm_dp_mst_atomic_check().
> > > + *
> > > + * 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))
> > > @@ -2637,20 +2650,41 @@ int drm_dp_atomic_find_vcpi_slots(struct
> > > drm_atomic_state *state,
> > >  	port = drm_dp_get_validated_port_ref(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_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;
> > > +			break;
> > > +		}
> > >  	}
> > > +	if (!vcpi)
> > > +		prev_slots = 0;
> > > +
> > > +	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
> > >  
> > > -	topology_state->avail_slots -= req_slots;
> > > -	DRM_DEBUG_KMS("vcpi slots avail=%d", topology_state->avail_slots);
> > > +	DRM_DEBUG_KMS("[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;
> > > +		}
> > > +
> > > +		vcpi->port = port;
> > > +		list_add(&vcpi->next, &topology_state->vcpis);
> > > +	}
> > > +	vcpi->vcpi = req_slots;
> > > +
> > > +	ret = req_slots;
> > > +out:
> > >  	drm_dp_put_port(port);
> > > -	return req_slots;
> > > +	return ret;
> > >  }
> > >  EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
> > >  
> > > @@ -2658,32 +2692,50 @@ 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).
> > > + *
> > > + * It is OK to call this even if @port has been removed from the
> > > system,
> > > in
> > > + * which case it will just amount to a no-op.
> > > + *
> > > + * 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 *tmp, *pos;
> > >  
> > >  	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_safe(pos, tmp, &topology_state->vcpis, next) {
> > > +		if (pos->port == port) {
> > > +			list_del(&pos->next);
> > > +			DRM_DEBUG_KMS("[MST PORT:%p] vcpi %d -> 0\n",
> > > +				      port, pos->vcpi);
> > >  
> > > +			kfree(pos);
> > > +			return 0;
> > > +		}
> > > +	}
> > > +
> > > +	/* If no allocation was found, all that means is that the port was
> > > +	 * destroyed since the last atomic commit. That's OK!
> > > +	 */
> > 
> > This case here has me a bit worried. I thought with your changes we'll
> > always have the port pointer still around, to be able to clean things up
> > properly. If this is not the case then we'd potentially leak the vcpi
> > allocation for an unplugged port.
> > 
> > Otoh if the driver releases the allocation for a port twice it's probably
> > mixed up it's own book-keeping. We should WARN about that case.
> > 
> > This is kinda fallout from your change to not prune allocations on
> > duplicate, and I think will further clean up how this is handled.
> > 
> > So with the comment removed and replaced by a WARNING(1,"no vcpi
> > allocation found for port %p\n", port) or something like that this should
> > be solid.
> 
> Hm; that comment is leftover from the fallout of moving the port
> verification
> logic out of the state duplicate functions, but I don't think this would
> nessecarily be a bookkeeping error. If we're going to support fallback
> link retraining, we'll need to make sure that every driver's
> drm_connector->atomic_check() function is idempotent so that if the
> atomic helpers have to pull in more CRTCs to perform modesets on then
> userspace originally added, the second check on the DRM connector
> doesn't cause any issues. Remember: if we're trying to retrain an MST
> topology at a lower link rate then before, that means changing the PBN
> divisor which in turn means that the only valid actions that can be
> taken are recalculating every active VCPI allocation at once in order to
> prevent state inconsistencies, or disabling all of the displays (since
> going from >0 VCPI to 0 VCPI should always be safe).
> 
> We /could/ just leave this up to the driver to do the bookkeeping on
> this, but that seems rather redundant. We could add extra bookkeeping in
> the atomic check though so that instead of just deleting the structs for
> each VCPI allocation when they go to 0, we instead just set them to 0
> then free them somewhere else.

jfyi; I think it would go something like this:

drm_dp_atomic_release_vcpi_slots():

for each vcpi:
  if vcpi.port == port:
    vcpi.vcpi = 0
    return 0;

drm_error("No previous VCPI allocation found! Help!!!\n");
return -EINVAL;

Then we'd need to add something to prune the VCPI allocations in the state,
which the driver would call after all atomic checks/mode validations have been
performed, including drm_dp_mst_atomic_check()

drm_dp_mst_atomic_check_finish():
  for each vcpi:
    if vcpi.vcpi == 0:
      del vcpi

Then, that way we've made sure that multiple VCPI frees in the same check are
OK, but freeing VCPI that never existed actually throws errors
> 
> > 
> > >  	return 0;
> > >  }
> > >  EXPORT_SYMBOL(drm_dp_atomic_release_vcpi_slots);
> > > @@ -3112,15 +3164,34 @@ 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) {
> > > +		vcpi = kmemdup(pos, sizeof(*vcpi), GFP_KERNEL);
> > > +		if (!vcpi)
> > > +			goto fail_alloc;
> > > +
> > > +		list_add(&vcpi->next, &state->vcpis);
> > > +	}
> > > +
> > >  	return &state->base;
> > > +
> > > +fail_alloc:
> > > +	list_for_each_entry_safe(pos, vcpi, &state->vcpis, next)
> > > +		kfree(pos);
> > > +	kfree(state);
> > > +
> > > +	return NULL;
> > >  }
> > >  
> > >  static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
> > > @@ -3128,14 +3199,99 @@ 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)
> > > +		kfree(pos);
> > >  
> > >  	kfree(mst_state);
> > >  }
> > >  
> > > -static const struct drm_private_state_funcs mst_state_funcs = {
> > > +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;
> > > +	struct drm_dp_mst_port *port;
> > > +	int avail_slots = 63, ret;
> > > +
> > > +	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
> > > +		/* Ports that no longer exist shouldn't be counted towards the
> > > +		 * bandwidth requirements for the state, so skip them
> > > +		 */
> > 
> > Scenario:
> > - 2 mst sinks on a single host side port.
> > - 1st connector is active, 2nd connector is off.
> > - 1st connector is hot-unplugged, but userspace hasn't realized this yet,
> >   so not yet come around to do the disabling modeset.
> > - At the same time userspace decides to enable the 2nd output, which
> >   forces a modeset and pulls the topology state in.
> > - This function here decides to only look at the vcpi allocation for the
> >   2nd connector because the first one is gone already.
> > - Unfortunately lighting up both connectors at the same time isn't
> >   possible, because too many vcpi. But since userspace didn't ask for a
> >   modeset on the now unplugged first connector.
> > -> Modeset goes boom because we enable too many vcpi.
> > 
> > But with the change in how we release vcpi allocations there's no need to
> > ignore disconnected stuff here, and we should be able to check vcpi limits
> > by just checking all of them.
> > 
> > I didn't see anything else serious, so with the above two things resolved
> > this has my Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> > 
> > One bikeshed below, because I need to prove I scrolled to the end :-)
> > 
> > > +		port = drm_dp_get_validated_port_ref(mgr, vcpi->port);
> > > +		if (!port) {
> > > +			DRM_DEBUG_ATOMIC("[MST PORT:%p] is stale, skipping
> > > checks\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);
> > > +			ret = -ENOSPC;
> > > +			goto port_fail;
> > > +		}
> > > +
> > > +		drm_dp_put_port(port);
> > > +	}
> > > +	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;
> > > +port_fail:
> > > +	drm_dp_put_port(port);
> > > +	return ret;
> > > +}
> > > +
> > > +/**
> > > + * 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,
> > >  };
> > > +EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);
> > >  
> > >  /**
> > >   * drm_atomic_get_mst_topology_state: get MST topology state
> > > @@ -3213,13 +3369,11 @@ 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(&mgr->base,
> > >  				    &mst_state->base,
> > > -				    &mst_state_funcs);
> > > +				    &drm_dp_mst_topology_state_funcs);
> > >  
> > >  	return 0;
> > >  }
> > > diff --git a/drivers/gpu/drm/i915/intel_display.c
> > > b/drivers/gpu/drm/i915/intel_display.c
> > > index bbf8ca21a7a2..8749cf61a6ac 100644
> > > --- a/drivers/gpu/drm/i915/intel_display.c
> > > +++ b/drivers/gpu/drm/i915/intel_display.c
> > > @@ -12553,6 +12553,10 @@ static int intel_atomic_check(struct drm_device
> > > *dev,
> > >  				       "[modeset]" : "[fastset]");
> > >  	}
> > >  
> > > +	ret = drm_dp_mst_atomic_check(state);
> > > +	if (ret)
> > > +		return ret;
> > 
> > Complete bikeshed, so feel free to ignore: I'd stuff this into
> > intel_modeset_checks(). Feel free to ignore.
> > 
> > Cheers, Daniel
> > 
> > > +
> > >  	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 8b71d64ebd9d..aaf904738b78 100644
> > > --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> > > +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> > > @@ -114,28 +114,31 @@ static int intel_dp_mst_atomic_check(struct
> > > drm_connector *connector,
> > >  	struct drm_connector_state *old_conn_state;
> > >  	struct drm_crtc *old_crtc;
> > >  	struct drm_crtc_state *crtc_state;
> > > -	int slots, ret = 0;
> > > +	struct intel_connector *intel_connector =
> > > +		to_intel_connector(connector);
> > > +	struct drm_dp_mst_topology_mgr *mgr =
> > > +		&intel_connector->mst_port->mst_mgr;
> > > +	struct drm_dp_mst_port *port = intel_connector->port;
> > > +	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;
> > > +	/* Free VCPI, since compute_config() won't be run */
> > > +	if (!new_conn_state->crtc) {
> > > +		crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
> > >  
> > > -		old_encoder = old_conn_state->best_encoder;
> > > -		mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
> > > -
> > > -		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;
> > > +		ret = drm_dp_atomic_release_vcpi_slots(state, mgr, port);
> > > +		if (ret) {
> > > +			DRM_DEBUG_KMS("failed releasing vcpi slots: %d\n",
> > > +				      ret);
> > > +			return ret;
> > > +		}
> > > +		to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
> > >  	}
> > > +
> > >  	return ret;
> > >  }
> > >  
> > > diff --git a/include/drm/drm_dp_mst_helper.h
> > > b/include/drm/drm_dp_mst_helper.h
> > > index 3faceb66f5cb..08b67948b8f9 100644
> > > --- a/include/drm/drm_dp_mst_helper.h
> > > +++ b/include/drm/drm_dp_mst_helper.h
> > > @@ -406,9 +406,15 @@ 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;
> > >  };
> > >  
> > > @@ -619,14 +625,17 @@ 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);
> > >  
> > >  extern const struct drm_private_state_funcs
> > > drm_dp_mst_topology_state_funcs;
> > >  
> > > -- 
> > > 2.19.1
> > > 
-- 
Cheers,
	Lyude Paul

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Re: [PATCH v3 2/5] drm/dp_mst: Start tracking per-port VCPI allocations

[Daniel Vetter]

On Wed, Nov 07, 2018 at 04:39:57PM -0500, Lyude Paul wrote:
> On Wed, 2018-11-07 at 16:23 -0500, Lyude Paul wrote:
> > On Wed, 2018-11-07 at 21:59 +0100, Daniel Vetter wrote:
> > > On Tue, Nov 06, 2018 at 08:21:14PM -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 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>
> > > > ---
> > > >  drivers/gpu/drm/drm_dp_mst_topology.c | 222 ++++++++++++++++++++++----
> > > >  drivers/gpu/drm/i915/intel_display.c  |   4 +
> > > >  drivers/gpu/drm/i915/intel_dp_mst.c   |  31 ++--
> > > >  include/drm/drm_dp_mst_helper.h       |  23 ++-
> > > >  4 files changed, 225 insertions(+), 55 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > index 8c3cfac437f4..74823afb262e 100644
> > > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > @@ -2614,21 +2614,34 @@ 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. The allocations are not
> > > > checked
> > > > + * against the bandwidth restraints of @mgr until the driver calls
> > > > + * drm_dp_mst_atomic_check().
> > > > + *
> > > > + * 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))
> > > > @@ -2637,20 +2650,41 @@ int drm_dp_atomic_find_vcpi_slots(struct
> > > > drm_atomic_state *state,
> > > >  	port = drm_dp_get_validated_port_ref(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_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;
> > > > +			break;
> > > > +		}
> > > >  	}
> > > > +	if (!vcpi)
> > > > +		prev_slots = 0;
> > > > +
> > > > +	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
> > > >  
> > > > -	topology_state->avail_slots -= req_slots;
> > > > -	DRM_DEBUG_KMS("vcpi slots avail=%d", topology_state->avail_slots);
> > > > +	DRM_DEBUG_KMS("[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;
> > > > +		}
> > > > +
> > > > +		vcpi->port = port;
> > > > +		list_add(&vcpi->next, &topology_state->vcpis);
> > > > +	}
> > > > +	vcpi->vcpi = req_slots;
> > > > +
> > > > +	ret = req_slots;
> > > > +out:
> > > >  	drm_dp_put_port(port);
> > > > -	return req_slots;
> > > > +	return ret;
> > > >  }
> > > >  EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
> > > >  
> > > > @@ -2658,32 +2692,50 @@ 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).
> > > > + *
> > > > + * It is OK to call this even if @port has been removed from the
> > > > system,
> > > > in
> > > > + * which case it will just amount to a no-op.
> > > > + *
> > > > + * 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 *tmp, *pos;
> > > >  
> > > >  	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_safe(pos, tmp, &topology_state->vcpis, next) {
> > > > +		if (pos->port == port) {
> > > > +			list_del(&pos->next);
> > > > +			DRM_DEBUG_KMS("[MST PORT:%p] vcpi %d -> 0\n",
> > > > +				      port, pos->vcpi);
> > > >  
> > > > +			kfree(pos);
> > > > +			return 0;
> > > > +		}
> > > > +	}
> > > > +
> > > > +	/* If no allocation was found, all that means is that the port was
> > > > +	 * destroyed since the last atomic commit. That's OK!
> > > > +	 */
> > > 
> > > This case here has me a bit worried. I thought with your changes we'll
> > > always have the port pointer still around, to be able to clean things up
> > > properly. If this is not the case then we'd potentially leak the vcpi
> > > allocation for an unplugged port.
> > > 
> > > Otoh if the driver releases the allocation for a port twice it's probably
> > > mixed up it's own book-keeping. We should WARN about that case.
> > > 
> > > This is kinda fallout from your change to not prune allocations on
> > > duplicate, and I think will further clean up how this is handled.
> > > 
> > > So with the comment removed and replaced by a WARNING(1,"no vcpi
> > > allocation found for port %p\n", port) or something like that this should
> > > be solid.
> > 
> > Hm; that comment is leftover from the fallout of moving the port
> > verification
> > logic out of the state duplicate functions, but I don't think this would
> > nessecarily be a bookkeeping error. If we're going to support fallback
> > link retraining, we'll need to make sure that every driver's
> > drm_connector->atomic_check() function is idempotent so that if the
> > atomic helpers have to pull in more CRTCs to perform modesets on then
> > userspace originally added, the second check on the DRM connector
> > doesn't cause any issues. Remember: if we're trying to retrain an MST
> > topology at a lower link rate then before, that means changing the PBN
> > divisor which in turn means that the only valid actions that can be
> > taken are recalculating every active VCPI allocation at once in order to
> > prevent state inconsistencies, or disabling all of the displays (since
> > going from >0 VCPI to 0 VCPI should always be safe).
> > 
> > We /could/ just leave this up to the driver to do the bookkeeping on
> > this, but that seems rather redundant. We could add extra bookkeeping in
> > the atomic check though so that instead of just deleting the structs for
> > each VCPI allocation when they go to 0, we instead just set them to 0
> > then free them somewhere else.
> 
> jfyi; I think it would go something like this:
> 
> drm_dp_atomic_release_vcpi_slots():
> 
> for each vcpi:
>   if vcpi.port == port:
>     vcpi.vcpi = 0
>     return 0;
> 
> drm_error("No previous VCPI allocation found! Help!!!\n");
> return -EINVAL;
> 
> Then we'd need to add something to prune the VCPI allocations in the state,
> which the driver would call after all atomic checks/mode validations have been
> performed, including drm_dp_mst_atomic_check()
> 
> drm_dp_mst_atomic_check_finish():
>   for each vcpi:
>     if vcpi.vcpi == 0:
>       del vcpi
> 
> Then, that way we've made sure that multiple VCPI frees in the same check are
> OK, but freeing VCPI that never existed actually throws errors

Not sure that's needed at all. The way link training works is we just ask
userspace to do the heavy lifting for us, by issuing a new modeset. If
that means mode pruning, we also ask userspace to do the heavy lifting for
us, again by issuing a new modeset. Kernel never needs to retrain if that
means recomputing state stuff or pruning modes or other fun problems. It
doesn't even need to retrain if that means shutting down a bunch of links,
it can just punt that to userspace and let it retrain at a convenient
time.

Of course that retrain might then result in a modeset, which might fail if
the connector is entirely gone by then.

Otoh I might just be talking nonsense right now, it's a bit late :-)

Cheers, Daniel


> > 
> > > 
> > > >  	return 0;
> > > >  }
> > > >  EXPORT_SYMBOL(drm_dp_atomic_release_vcpi_slots);
> > > > @@ -3112,15 +3164,34 @@ 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) {
> > > > +		vcpi = kmemdup(pos, sizeof(*vcpi), GFP_KERNEL);
> > > > +		if (!vcpi)
> > > > +			goto fail_alloc;
> > > > +
> > > > +		list_add(&vcpi->next, &state->vcpis);
> > > > +	}
> > > > +
> > > >  	return &state->base;
> > > > +
> > > > +fail_alloc:
> > > > +	list_for_each_entry_safe(pos, vcpi, &state->vcpis, next)
> > > > +		kfree(pos);
> > > > +	kfree(state);
> > > > +
> > > > +	return NULL;
> > > >  }
> > > >  
> > > >  static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
> > > > @@ -3128,14 +3199,99 @@ 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)
> > > > +		kfree(pos);
> > > >  
> > > >  	kfree(mst_state);
> > > >  }
> > > >  
> > > > -static const struct drm_private_state_funcs mst_state_funcs = {
> > > > +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;
> > > > +	struct drm_dp_mst_port *port;
> > > > +	int avail_slots = 63, ret;
> > > > +
> > > > +	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
> > > > +		/* Ports that no longer exist shouldn't be counted towards the
> > > > +		 * bandwidth requirements for the state, so skip them
> > > > +		 */
> > > 
> > > Scenario:
> > > - 2 mst sinks on a single host side port.
> > > - 1st connector is active, 2nd connector is off.
> > > - 1st connector is hot-unplugged, but userspace hasn't realized this yet,
> > >   so not yet come around to do the disabling modeset.
> > > - At the same time userspace decides to enable the 2nd output, which
> > >   forces a modeset and pulls the topology state in.
> > > - This function here decides to only look at the vcpi allocation for the
> > >   2nd connector because the first one is gone already.
> > > - Unfortunately lighting up both connectors at the same time isn't
> > >   possible, because too many vcpi. But since userspace didn't ask for a
> > >   modeset on the now unplugged first connector.
> > > -> Modeset goes boom because we enable too many vcpi.
> > > 
> > > But with the change in how we release vcpi allocations there's no need to
> > > ignore disconnected stuff here, and we should be able to check vcpi limits
> > > by just checking all of them.
> > > 
> > > I didn't see anything else serious, so with the above two things resolved
> > > this has my Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > 
> > > One bikeshed below, because I need to prove I scrolled to the end :-)
> > > 
> > > > +		port = drm_dp_get_validated_port_ref(mgr, vcpi->port);
> > > > +		if (!port) {
> > > > +			DRM_DEBUG_ATOMIC("[MST PORT:%p] is stale, skipping
> > > > checks\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);
> > > > +			ret = -ENOSPC;
> > > > +			goto port_fail;
> > > > +		}
> > > > +
> > > > +		drm_dp_put_port(port);
> > > > +	}
> > > > +	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;
> > > > +port_fail:
> > > > +	drm_dp_put_port(port);
> > > > +	return ret;
> > > > +}
> > > > +
> > > > +/**
> > > > + * 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,
> > > >  };
> > > > +EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);
> > > >  
> > > >  /**
> > > >   * drm_atomic_get_mst_topology_state: get MST topology state
> > > > @@ -3213,13 +3369,11 @@ 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(&mgr->base,
> > > >  				    &mst_state->base,
> > > > -				    &mst_state_funcs);
> > > > +				    &drm_dp_mst_topology_state_funcs);
> > > >  
> > > >  	return 0;
> > > >  }
> > > > diff --git a/drivers/gpu/drm/i915/intel_display.c
> > > > b/drivers/gpu/drm/i915/intel_display.c
> > > > index bbf8ca21a7a2..8749cf61a6ac 100644
> > > > --- a/drivers/gpu/drm/i915/intel_display.c
> > > > +++ b/drivers/gpu/drm/i915/intel_display.c
> > > > @@ -12553,6 +12553,10 @@ static int intel_atomic_check(struct drm_device
> > > > *dev,
> > > >  				       "[modeset]" : "[fastset]");
> > > >  	}
> > > >  
> > > > +	ret = drm_dp_mst_atomic_check(state);
> > > > +	if (ret)
> > > > +		return ret;
> > > 
> > > Complete bikeshed, so feel free to ignore: I'd stuff this into
> > > intel_modeset_checks(). Feel free to ignore.
> > > 
> > > Cheers, Daniel
> > > 
> > > > +
> > > >  	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 8b71d64ebd9d..aaf904738b78 100644
> > > > --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> > > > +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> > > > @@ -114,28 +114,31 @@ static int intel_dp_mst_atomic_check(struct
> > > > drm_connector *connector,
> > > >  	struct drm_connector_state *old_conn_state;
> > > >  	struct drm_crtc *old_crtc;
> > > >  	struct drm_crtc_state *crtc_state;
> > > > -	int slots, ret = 0;
> > > > +	struct intel_connector *intel_connector =
> > > > +		to_intel_connector(connector);
> > > > +	struct drm_dp_mst_topology_mgr *mgr =
> > > > +		&intel_connector->mst_port->mst_mgr;
> > > > +	struct drm_dp_mst_port *port = intel_connector->port;
> > > > +	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;
> > > > +	/* Free VCPI, since compute_config() won't be run */
> > > > +	if (!new_conn_state->crtc) {
> > > > +		crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
> > > >  
> > > > -		old_encoder = old_conn_state->best_encoder;
> > > > -		mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
> > > > -
> > > > -		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;
> > > > +		ret = drm_dp_atomic_release_vcpi_slots(state, mgr, port);
> > > > +		if (ret) {
> > > > +			DRM_DEBUG_KMS("failed releasing vcpi slots: %d\n",
> > > > +				      ret);
> > > > +			return ret;
> > > > +		}
> > > > +		to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
> > > >  	}
> > > > +
> > > >  	return ret;
> > > >  }
> > > >  
> > > > diff --git a/include/drm/drm_dp_mst_helper.h
> > > > b/include/drm/drm_dp_mst_helper.h
> > > > index 3faceb66f5cb..08b67948b8f9 100644
> > > > --- a/include/drm/drm_dp_mst_helper.h
> > > > +++ b/include/drm/drm_dp_mst_helper.h
> > > > @@ -406,9 +406,15 @@ 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;
> > > >  };
> > > >  
> > > > @@ -619,14 +625,17 @@ 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);
> > > >  
> > > >  extern const struct drm_private_state_funcs
> > > > drm_dp_mst_topology_state_funcs;
> > > >  
> > > > -- 
> > > > 2.19.1
> > > > 
> -- 
> Cheers,
> 	Lyude Paul
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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✓ Fi.CI.IGT: success for drm/dp_mst: Add some atomic state iterator macros

[Patchwork]

== Series Details ==

Series: drm/dp_mst: Add some atomic state iterator macros
URL   : https://patchwork.freedesktop.org/series/52130/
State : success

== Summary ==

= CI Bug Log - changes from CI_DRM_5097_full -> Patchwork_10749_full =

== Summary - WARNING ==

  Minor unknown changes coming with Patchwork_10749_full need to be verified
  manually.
  
  If you think the reported changes have nothing to do with the changes
  introduced in Patchwork_10749_full, please notify your bug team to allow them
  to document this new failure mode, which will reduce false positives in CI.

  

== Possible new issues ==

  Here are the unknown changes that may have been introduced in Patchwork_10749_full:

  === IGT changes ===

    ==== Warnings ====

    igt@pm_rc6_residency@rc6-accuracy:
      shard-snb:          PASS -> SKIP

    
== Known issues ==

  Here are the changes found in Patchwork_10749_full that come from known issues:

  === IGT changes ===

    ==== Issues hit ====

    igt@gem_exec_store@basic-vebox:
      shard-kbl:          PASS -> DMESG-WARN (fdo#105602, fdo#103558) +9

    igt@gem_workarounds@suspend-resume:
      shard-skl:          PASS -> INCOMPLETE (fdo#107773, fdo#104108)

    igt@kms_busy@extended-modeset-hang-newfb-render-a:
      shard-skl:          NOTRUN -> DMESG-WARN (fdo#107956) +1

    igt@kms_busy@extended-modeset-hang-newfb-with-reset-render-c:
      shard-apl:          NOTRUN -> DMESG-WARN (fdo#107956)

    igt@kms_color@pipe-b-legacy-gamma:
      shard-apl:          PASS -> FAIL (fdo#104782)

    igt@kms_cursor_crc@cursor-128x128-onscreen:
      shard-apl:          PASS -> FAIL (fdo#103232) +1

    igt@kms_cursor_crc@cursor-128x42-sliding:
      shard-apl:          NOTRUN -> FAIL (fdo#103232) +1

    igt@kms_flip@dpms-off-confusion-interruptible:
      shard-apl:          PASS -> INCOMPLETE (fdo#103927)

    igt@kms_flip@flip-vs-expired-vblank:
      shard-skl:          PASS -> FAIL (fdo#105363)

    igt@kms_frontbuffer_tracking@fbc-1p-primscrn-spr-indfb-draw-mmap-cpu:
      shard-apl:          PASS -> FAIL (fdo#103167) +3

    igt@kms_plane_alpha_blend@pipe-b-alpha-transparant-fb:
      shard-skl:          NOTRUN -> FAIL (fdo#108145) +1

    igt@kms_plane_multiple@atomic-pipe-a-tiling-yf:
      shard-apl:          PASS -> FAIL (fdo#103166) +1

    igt@kms_properties@connector-properties-atomic:
      shard-skl:          NOTRUN -> FAIL (fdo#108642)

    igt@pm_rpm@system-suspend-execbuf:
      shard-skl:          PASS -> INCOMPLETE (fdo#107773, fdo#104108, fdo#107807)

    igt@prime_busy@basic-wait-before-default:
      shard-snb:          PASS -> INCOMPLETE (fdo#105411)

    
    ==== Possible fixes ====

    igt@gem_ctx_isolation@vecs0-s3:
      shard-skl:          INCOMPLETE (fdo#107773, fdo#104108) -> PASS

    igt@gem_exec_reuse@baggage:
      shard-apl:          DMESG-WARN -> PASS

    igt@kms_busy@extended-pageflip-modeset-hang-oldfb-render-b:
      shard-kbl:          DMESG-WARN (fdo#107956) -> PASS

    igt@kms_color@pipe-a-ctm-max:
      shard-apl:          FAIL (fdo#108147) -> PASS

    igt@kms_cursor_crc@cursor-256x256-random:
      shard-apl:          FAIL (fdo#103232) -> PASS +5

    igt@kms_cursor_crc@cursor-256x256-suspend:
      shard-apl:          FAIL (fdo#103232, fdo#103191) -> PASS

    igt@kms_flip@flip-vs-expired-vblank-interruptible:
      shard-skl:          FAIL (fdo#105363) -> PASS

    igt@kms_flip_tiling@flip-to-yf-tiled:
      shard-skl:          FAIL (fdo#107931) -> PASS

    igt@kms_frontbuffer_tracking@fbc-1p-offscren-pri-shrfb-draw-render:
      shard-skl:          FAIL (fdo#105682) -> PASS

    igt@kms_frontbuffer_tracking@fbc-1p-primscrn-spr-indfb-draw-pwrite:
      shard-apl:          FAIL (fdo#103167) -> PASS +3

    igt@kms_frontbuffer_tracking@psr-1p-primscrn-pri-indfb-draw-pwrite:
      shard-skl:          FAIL (fdo#103167) -> PASS +1

    igt@kms_pipe_crc_basic@suspend-read-crc-pipe-b:
      shard-apl:          INCOMPLETE (fdo#103927) -> PASS +1

    igt@kms_plane_alpha_blend@pipe-c-coverage-7efc:
      shard-skl:          FAIL (fdo#107815) -> PASS +1

    igt@kms_plane_multiple@atomic-pipe-a-tiling-y:
      shard-apl:          FAIL (fdo#103166) -> PASS

    igt@kms_plane_multiple@atomic-pipe-a-tiling-yf:
      shard-glk:          FAIL (fdo#103166) -> PASS

    igt@kms_vblank@pipe-a-accuracy-idle:
      shard-skl:          FAIL (fdo#102583) -> PASS

    igt@pm_rpm@dpms-lpsp:
      shard-skl:          INCOMPLETE (fdo#107807) -> PASS

    
  fdo#102583 https://bugs.freedesktop.org/show_bug.cgi?id=102583
  fdo#103166 https://bugs.freedesktop.org/show_bug.cgi?id=103166
  fdo#103167 https://bugs.freedesktop.org/show_bug.cgi?id=103167
  fdo#103191 https://bugs.freedesktop.org/show_bug.cgi?id=103191
  fdo#103232 https://bugs.freedesktop.org/show_bug.cgi?id=103232
  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#105363 https://bugs.freedesktop.org/show_bug.cgi?id=105363
  fdo#105411 https://bugs.freedesktop.org/show_bug.cgi?id=105411
  fdo#105602 https://bugs.freedesktop.org/show_bug.cgi?id=105602
  fdo#105682 https://bugs.freedesktop.org/show_bug.cgi?id=105682
  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#107931 https://bugs.freedesktop.org/show_bug.cgi?id=107931
  fdo#107956 https://bugs.freedesktop.org/show_bug.cgi?id=107956
  fdo#108145 https://bugs.freedesktop.org/show_bug.cgi?id=108145
  fdo#108147 https://bugs.freedesktop.org/show_bug.cgi?id=108147
  fdo#108642 https://bugs.freedesktop.org/show_bug.cgi?id=108642


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

  No changes in participating hosts


== Build changes ==

    * Linux: CI_DRM_5097 -> Patchwork_10749

  CI_DRM_5097: c20dfc4f015dfd41246beb7d72338aa50543a5ef @ git://anongit.freedesktop.org/gfx-ci/linux
  IGT_4711: cc41f4c921e56c62c85ec5349c47022ae9b5f008 @ git://anongit.freedesktop.org/xorg/app/intel-gpu-tools
  Patchwork_10749: b58c9476ea09620366de5a2ba7ecbcd01a5a8962 @ 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_10749/shards.html
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Re: [PATCH v3 2/5] drm/dp_mst: Start tracking per-port VCPI allocations

[Lyude Paul]

On Wed, 2018-11-07 at 22:59 +0100, Daniel Vetter wrote:
> On Wed, Nov 07, 2018 at 04:39:57PM -0500, Lyude Paul wrote:
> > On Wed, 2018-11-07 at 16:23 -0500, Lyude Paul wrote:
> > > On Wed, 2018-11-07 at 21:59 +0100, Daniel Vetter wrote:
> > > > On Tue, Nov 06, 2018 at 08:21:14PM -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 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>
> > > > > ---
> > > > >  drivers/gpu/drm/drm_dp_mst_topology.c | 222 ++++++++++++++++++++++-
> > > > > ---
> > > > >  drivers/gpu/drm/i915/intel_display.c  |   4 +
> > > > >  drivers/gpu/drm/i915/intel_dp_mst.c   |  31 ++--
> > > > >  include/drm/drm_dp_mst_helper.h       |  23 ++-
> > > > >  4 files changed, 225 insertions(+), 55 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > index 8c3cfac437f4..74823afb262e 100644
> > > > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > @@ -2614,21 +2614,34 @@ 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. The allocations are
> > > > > not
> > > > > checked
> > > > > + * against the bandwidth restraints of @mgr until the driver calls
> > > > > + * drm_dp_mst_atomic_check().
> > > > > + *
> > > > > + * 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))
> > > > > @@ -2637,20 +2650,41 @@ int drm_dp_atomic_find_vcpi_slots(struct
> > > > > drm_atomic_state *state,
> > > > >  	port = drm_dp_get_validated_port_ref(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_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;
> > > > > +			break;
> > > > > +		}
> > > > >  	}
> > > > > +	if (!vcpi)
> > > > > +		prev_slots = 0;
> > > > > +
> > > > > +	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
> > > > >  
> > > > > -	topology_state->avail_slots -= req_slots;
> > > > > -	DRM_DEBUG_KMS("vcpi slots avail=%d", topology_state-
> > > > > >avail_slots);
> > > > > +	DRM_DEBUG_KMS("[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;
> > > > > +		}
> > > > > +
> > > > > +		vcpi->port = port;
> > > > > +		list_add(&vcpi->next, &topology_state->vcpis);
> > > > > +	}
> > > > > +	vcpi->vcpi = req_slots;
> > > > > +
> > > > > +	ret = req_slots;
> > > > > +out:
> > > > >  	drm_dp_put_port(port);
> > > > > -	return req_slots;
> > > > > +	return ret;
> > > > >  }
> > > > >  EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
> > > > >  
> > > > > @@ -2658,32 +2692,50 @@
> > > > > 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).
> > > > > + *
> > > > > + * It is OK to call this even if @port has been removed from the
> > > > > system,
> > > > > in
> > > > > + * which case it will just amount to a no-op.
> > > > > + *
> > > > > + * 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 *tmp, *pos;
> > > > >  
> > > > >  	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_safe(pos, tmp, &topology_state->vcpis,
> > > > > next) {
> > > > > +		if (pos->port == port) {
> > > > > +			list_del(&pos->next);
> > > > > +			DRM_DEBUG_KMS("[MST PORT:%p] vcpi %d -> 0\n",
> > > > > +				      port, pos->vcpi);
> > > > >  
> > > > > +			kfree(pos);
> > > > > +			return 0;
> > > > > +		}
> > > > > +	}
> > > > > +
> > > > > +	/* If no allocation was found, all that means is that the port
> > > > > was
> > > > > +	 * destroyed since the last atomic commit. That's OK!
> > > > > +	 */
> > > > 
> > > > This case here has me a bit worried. I thought with your changes we'll
> > > > always have the port pointer still around, to be able to clean things
> > > > up
> > > > properly. If this is not the case then we'd potentially leak the vcpi
> > > > allocation for an unplugged port.
> > > > 
> > > > Otoh if the driver releases the allocation for a port twice it's
> > > > probably
> > > > mixed up it's own book-keeping. We should WARN about that case.
> > > > 
> > > > This is kinda fallout from your change to not prune allocations on
> > > > duplicate, and I think will further clean up how this is handled.
> > > > 
> > > > So with the comment removed and replaced by a WARNING(1,"no vcpi
> > > > allocation found for port %p\n", port) or something like that this
> > > > should
> > > > be solid.
> > > 
> > > Hm; that comment is leftover from the fallout of moving the port
> > > verification
> > > logic out of the state duplicate functions, but I don't think this would
> > > nessecarily be a bookkeeping error. If we're going to support fallback
> > > link retraining, we'll need to make sure that every driver's
> > > drm_connector->atomic_check() function is idempotent so that if the
> > > atomic helpers have to pull in more CRTCs to perform modesets on then
> > > userspace originally added, the second check on the DRM connector
> > > doesn't cause any issues. Remember: if we're trying to retrain an MST
> > > topology at a lower link rate then before, that means changing the PBN
> > > divisor which in turn means that the only valid actions that can be
> > > taken are recalculating every active VCPI allocation at once in order to
> > > prevent state inconsistencies, or disabling all of the displays (since
> > > going from >0 VCPI to 0 VCPI should always be safe).
> > > 
> > > We /could/ just leave this up to the driver to do the bookkeeping on
> > > this, but that seems rather redundant. We could add extra bookkeeping in
> > > the atomic check though so that instead of just deleting the structs for
> > > each VCPI allocation when they go to 0, we instead just set them to 0
> > > then free them somewhere else.
> > 
> > jfyi; I think it would go something like this:
> > 
> > drm_dp_atomic_release_vcpi_slots():
> > 
> > for each vcpi:
> >   if vcpi.port == port:
> >     vcpi.vcpi = 0
> >     return 0;
> > 
> > drm_error("No previous VCPI allocation found! Help!!!\n");
> > return -EINVAL;
> > 
> > Then we'd need to add something to prune the VCPI allocations in the
> > state,
> > which the driver would call after all atomic checks/mode validations have
> > been
> > performed, including drm_dp_mst_atomic_check()
> > 
> > drm_dp_mst_atomic_check_finish():
> >   for each vcpi:
> >     if vcpi.vcpi == 0:
> >       del vcpi
> > 
> > Then, that way we've made sure that multiple VCPI frees in the same check
> > are
> > OK, but freeing VCPI that never existed actually throws errors
> 
> Not sure that's needed at all. The way link training works is we just ask
> userspace to do the heavy lifting for us, by issuing a new modeset. If
> that means mode pruning, we also ask userspace to do the heavy lifting for
> us, again by issuing a new modeset. Kernel never needs to retrain if that
> means recomputing state stuff or pruning modes or other fun problems. It
> doesn't even need to retrain if that means shutting down a bunch of links,
> it can just punt that to userspace and let it retrain at a convenient
> time.
> 
> Of course that retrain might then result in a modeset, which might fail if
> the connector is entirely gone by then.
> 
> Otoh I might just be talking nonsense right now, it's a bit late :-)

hehe-it's fine. Either way, I'll try to explain it a little better to make
this easier to understand for tommorrow.

So: the VCPI allocations are all calculated based on the topology's PBN
divisor, which itself is calculated based on the link rate and bandwidth. For
a topology running at 5.4 GBit/s x 4 lanes, the pbn_divisor would be 40. For
2.7GBit/s x 4 lanes, it would be 20. The higher the PBN divisor, the more VCPI
tokens are needed for each active display, and vice versa.

So: let's say we have a topology like this:

DP-1 @ 5.4 GBit/s w/ pbn_div == 40:
 |- DP-4: 1920x1080 @ 60Hz bpp=24, VCPI = 14
 |- DP-5: 1920x1080 @ 60Hz bpp=24, VCPI = 14

As a note: because DP-4 and DP-5 share the same DP link since they're on
the same topology, I'm assuming that LINK_STATUS_BAD is set at once for
all of them.

If DP-4 and DP-5's connection status suddenly went LINK_STATUS_BAD, we'd
need to recalculate everything to fit in 2.7 GBit/s with a pbn_div of
20. This is the important part: remember that since everything's sharing
the same link, that means they're also sharing the same PBN divisor.
Which means that if userspace were to try to fix this by changing one
display at a time, say:

DP-1 @ 2.7 GBit/s w/ pbn_div == 20: (Invalid state)
 |- DP-4: 1920x1080 @ 60Hz bpp=24, VCPI=28
 |- DP-5: 1920x1080 @ 60Hz bpp=24, VCPI=14

This wouldn't work at all: the 14 VCPI slots that DP-5 has now
correspond to half the amount of real-world bandwidth then they did
previously. This would be broken, and additionally the MST spec mandates
that in the event that the all payloads need to be recalculated on link
rate changes before programming new payloads.. So, that means we're only
left with a few ways to fix this. Change DP-4 and DP-5 at the same time:

DP-1 @ 2.7 GBit/s w/ pbn_div == 20: (Link good, valid state)
 |- DP-4: 1920x1080 @ 60Hz bpp=24, VCPI=28
 |- DP-5: 1920x1080 @ 60Hz bpp=24, VCPI=28

Or disable each connector. This can be done all at once, or one at a
time since we're not programming new payloads:

DP-1 @ 5.4 GBit/s w/ pbn_div == 40: (Link bad, valid state)
 |- DP-4: 1920x1080 @ 60Hz bpp=24, VCPI = 14
 |- DP-5: <disabled>

DP-1 @ 2.7 GBit/s w/ pbn_div == 20: (Link good, valid state)
 |- DP-4: <disabled>
 |- DP-5: <disabled>

What this means for atomic userspace is that while it is a bit
complicated, we do actually need to add restrictions on what modesets it
tries to do on topologies that need fallback retraining to prevent it
from setting an invalid state like the one shown above. Part of this
means that if userspace tries to do a modeset on one connector on a
topology, we have to force a modeset on all of the other connectors on
the topology to ensure that they still fit within the VCPI restrictions
after having their allocations recalculated. /THIS/ is where having
everything that the atomic MST helpers do be idempotent comes in handy
as it would solve a situation like this:

(assuming the current setup is identical to the diagrams I listed above)

Atomic state containing:
 - mgr w/ pbn_div == 40 (link @ 5.4 GBit/s)
 - DP-4: 1920x1080 @ 60Hz bpp=24, VCPI=14
   - LINK_STATUS bad -> good (requires modeset to apply new VCPI of 28)

DP-4 encoder.atomic_check() -> OK
DP-4.atomic_check() -> OK

mgr.atomic_check() -> nono wait a second userspace!!
 - DP-4 can't be changed without changing DP-5, so:
   state.add_connector(DP-5)
   DP-5.mode_changed = true
   need_recheck = true

state.recheck():
 # Rerun checks now
 DP-4 encoder.atomic_check() -> OK
 DP-4.atomic_check() -> OK
 DP-5 encoder.atomic_check() -> OK
 DP-5.atomic_check() -> OK
 mgr.atomic_check() -> OK

As you can see: DP-4 needed to get checked a second time, which means
it's VCPI would be freed twice in the same state, but nothing would
actually be leaking! That's pretty much the whole usecase for something
like this, so that drivers don't have to track where they are in their
atomic check() since that's a lot more error prone to have rewritten
once for each MST driver.

> 
> Cheers, Daniel
> 
> 
> > > > >  	return 0;
> > > > >  }
> > > > >  EXPORT_SYMBOL(drm_dp_atomic_release_vcpi_slots);
> > > > > @@ -3112,15 +3164,34 @@ 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) {
> > > > > +		vcpi = kmemdup(pos, sizeof(*vcpi), GFP_KERNEL);
> > > > > +		if (!vcpi)
> > > > > +			goto fail_alloc;
> > > > > +
> > > > > +		list_add(&vcpi->next, &state->vcpis);
> > > > > +	}
> > > > > +
> > > > >  	return &state->base;
> > > > > +
> > > > > +fail_alloc:
> > > > > +	list_for_each_entry_safe(pos, vcpi, &state->vcpis, next)
> > > > > +		kfree(pos);
> > > > > +	kfree(state);
> > > > > +
> > > > > +	return NULL;
> > > > >  }
> > > > >  
> > > > >  static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
> > > > > @@ -3128,14 +3199,99 @@ 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)
> > > > > +		kfree(pos);
> > > > >  
> > > > >  	kfree(mst_state);
> > > > >  }
> > > > >  
> > > > > -static const struct drm_private_state_funcs mst_state_funcs = {
> > > > > +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;
> > > > > +	struct drm_dp_mst_port *port;
> > > > > +	int avail_slots = 63, ret;
> > > > > +
> > > > > +	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
> > > > > +		/* Ports that no longer exist shouldn't be counted
> > > > > towards the
> > > > > +		 * bandwidth requirements for the state, so skip them
> > > > > +		 */
> > > > 
> > > > Scenario:
> > > > - 2 mst sinks on a single host side port.
> > > > - 1st connector is active, 2nd connector is off.
> > > > - 1st connector is hot-unplugged, but userspace hasn't realized this
> > > > yet,
> > > >   so not yet come around to do the disabling modeset.
> > > > - At the same time userspace decides to enable the 2nd output, which
> > > >   forces a modeset and pulls the topology state in.
> > > > - This function here decides to only look at the vcpi allocation for
> > > > the
> > > >   2nd connector because the first one is gone already.
> > > > - Unfortunately lighting up both connectors at the same time isn't
> > > >   possible, because too many vcpi. But since userspace didn't ask for
> > > > a
> > > >   modeset on the now unplugged first connector.
> > > > -> Modeset goes boom because we enable too many vcpi.
> > > > 
> > > > But with the change in how we release vcpi allocations there's no need
> > > > to
> > > > ignore disconnected stuff here, and we should be able to check vcpi
> > > > limits
> > > > by just checking all of them.
> > > > 
> > > > I didn't see anything else serious, so with the above two things
> > > > resolved
> > > > this has my Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > > 
> > > > One bikeshed below, because I need to prove I scrolled to the end :-)
> > > > 
> > > > > +		port = drm_dp_get_validated_port_ref(mgr, vcpi->port);
> > > > > +		if (!port) {
> > > > > +			DRM_DEBUG_ATOMIC("[MST PORT:%p] is stale,
> > > > > skipping
> > > > > checks\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);
> > > > > +			ret = -ENOSPC;
> > > > > +			goto port_fail;
> > > > > +		}
> > > > > +
> > > > > +		drm_dp_put_port(port);
> > > > > +	}
> > > > > +	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;
> > > > > +port_fail:
> > > > > +	drm_dp_put_port(port);
> > > > > +	return ret;
> > > > > +}
> > > > > +
> > > > > +/**
> > > > > + * 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,
> > > > >  };
> > > > > +EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);
> > > > >  
> > > > >  /**
> > > > >   * drm_atomic_get_mst_topology_state: get MST topology state
> > > > > @@ -3213,13 +3369,11 @@ 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(&mgr->base,
> > > > >  				    &mst_state->base,
> > > > > -				    &mst_state_funcs);
> > > > > +				    &drm_dp_mst_topology_state_funcs);
> > > > >  
> > > > >  	return 0;
> > > > >  }
> > > > > diff --git a/drivers/gpu/drm/i915/intel_display.c
> > > > > b/drivers/gpu/drm/i915/intel_display.c
> > > > > index bbf8ca21a7a2..8749cf61a6ac 100644
> > > > > --- a/drivers/gpu/drm/i915/intel_display.c
> > > > > +++ b/drivers/gpu/drm/i915/intel_display.c
> > > > > @@ -12553,6 +12553,10 @@ static int intel_atomic_check(struct
> > > > > drm_device
> > > > > *dev,
> > > > >  				       "[modeset]" : "[fastset]");
> > > > >  	}
> > > > >  
> > > > > +	ret = drm_dp_mst_atomic_check(state);
> > > > > +	if (ret)
> > > > > +		return ret;
> > > > 
> > > > Complete bikeshed, so feel free to ignore: I'd stuff this into
> > > > intel_modeset_checks(). Feel free to ignore.
> > > > 
> > > > Cheers, Daniel
> > > > 
> > > > > +
> > > > >  	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 8b71d64ebd9d..aaf904738b78 100644
> > > > > --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> > > > > +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> > > > > @@ -114,28 +114,31 @@ static int intel_dp_mst_atomic_check(struct
> > > > > drm_connector *connector,
> > > > >  	struct drm_connector_state *old_conn_state;
> > > > >  	struct drm_crtc *old_crtc;
> > > > >  	struct drm_crtc_state *crtc_state;
> > > > > -	int slots, ret = 0;
> > > > > +	struct intel_connector *intel_connector =
> > > > > +		to_intel_connector(connector);
> > > > > +	struct drm_dp_mst_topology_mgr *mgr =
> > > > > +		&intel_connector->mst_port->mst_mgr;
> > > > > +	struct drm_dp_mst_port *port = intel_connector->port;
> > > > > +	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;
> > > > > +	/* Free VCPI, since compute_config() won't be run */
> > > > > +	if (!new_conn_state->crtc) {
> > > > > +		crtc_state = drm_atomic_get_new_crtc_state(state,
> > > > > old_crtc);
> > > > >  
> > > > > -		old_encoder = old_conn_state->best_encoder;
> > > > > -		mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
> > > > > -
> > > > > -		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;
> > > > > +		ret = drm_dp_atomic_release_vcpi_slots(state, mgr,
> > > > > port);
> > > > > +		if (ret) {
> > > > > +			DRM_DEBUG_KMS("failed releasing vcpi slots:
> > > > > %d\n",
> > > > > +				      ret);
> > > > > +			return ret;
> > > > > +		}
> > > > > +		to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
> > > > >  	}
> > > > > +
> > > > >  	return ret;
> > > > >  }
> > > > >  
> > > > > diff --git a/include/drm/drm_dp_mst_helper.h
> > > > > b/include/drm/drm_dp_mst_helper.h
> > > > > index 3faceb66f5cb..08b67948b8f9 100644
> > > > > --- a/include/drm/drm_dp_mst_helper.h
> > > > > +++ b/include/drm/drm_dp_mst_helper.h
> > > > > @@ -406,9 +406,15 @@ 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;
> > > > >  };
> > > > >  
> > > > > @@ -619,14 +625,17 @@ 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,
> > > > >  								    st
> > > > > ruct
> > > > > 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);
> > > > >  
> > > > >  extern const struct drm_private_state_funcs
> > > > > drm_dp_mst_topology_state_funcs;
> > > > >  
> > > > > -- 
> > > > > 2.19.1
> > > > > 
> > -- 
> > Cheers,
> > 	Lyude Paul
> > 
-- 
Cheers,
	Lyude Paul

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