[PATCH 17/17] drm/atomic: Refcounting for plane_state->fb

[Daniel Vetter <daniel.vetter@ffwll.ch>]

So my original plan was that the drm core refcounts framebuffers like
with the legacy ioctls. But that doesn't work for a bunch of reasons:

- State objects might live longer than until the next fb change
  happens for a plane. For example delayed cleanup work only happens
  _after_ the pageflip ioctl has completed. So this definitely doesn't
  work without the plane state holding its own refernces.

- The other issue is transition from legacy to atomic implementations,
  where the driver works under a mix of both worlds. Which means
  legacy paths might not properly update the ->fb pointer under
  plane->state->fb. Which is a bit a problem when then someone comes
  around and _does_ try to clean it up when it's long gone.

The second issue is just a bit a transition bug, since drivers should
update plane->state->fb in all the paths that aren't converted yet.
But a bit more robustness for the transition cant' hurt - we pull
similar tricks with cleaning up the old fb in the transitional helpers
already.

The pattern for drivers that transition is

	if (plane->state)
		drm_atomic_set_fb_for_plane(plane->state, plane->fb);

inserted after the fb update has logically completed at the end of
->set_config (or ->set_base/mode_set if using the crtc helpers),
->page_flip, ->update_plane or any other entry point which updates
plane->fb.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
---
 drivers/gpu/drm/drm_atomic.c        | 27 +++++++++++++++++++++++++++
 drivers/gpu/drm/drm_atomic_helper.c | 25 +++++++++++++++++++------
 drivers/gpu/drm/drm_crtc_helper.c   |  7 ++++---
 drivers/gpu/drm/drm_plane_helper.c  | 14 +++++++-------
 include/drm/drm_atomic.h            |  2 ++
 5 files changed, 59 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index c6db8a48cad6..af34321b675d 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -366,6 +366,33 @@ drm_atomic_set_crtc_for_plane(struct drm_plane_state *plane_state,
 EXPORT_SYMBOL(drm_atomic_set_crtc_for_plane);
 
 /**
+ * drm_atomic_set_fb_for_plane - set crtc for plane
+ * @plane_state: atomic state object for the plane
+ * @fb: fb to use for the plane
+ *
+ * Changing the assigned crtc for a plane requires us to grab the lock and state
+ * for the new crtc, as needed. This function takes care of all these details
+ * besides updating the pointer in the state object itself.
+ */
+void
+drm_atomic_set_fb_for_plane(struct drm_plane_state *plane_state,
+			    struct drm_framebuffer *fb)
+{
+	if (plane_state->fb)
+		drm_framebuffer_unreference(plane_state->fb);
+	if (fb)
+		drm_framebuffer_reference(fb);
+	plane_state->fb = fb;
+
+	if (fb)
+		DRM_DEBUG_KMS("Set [FB:%d] for plane state %p\n",
+			      fb->base.id, plane_state);
+	else
+		DRM_DEBUG_KMS("Set [NOFB] for plane state %p\n", plane_state);
+}
+EXPORT_SYMBOL(drm_atomic_set_fb_for_plane);
+
+/**
  * drm_atomic_set_crtc_for_connector - set crtc for connector
  * @conn_state: atomic state object for the connector
  * @crtc: crtc to use for the connector
diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index d0ca681d6326..a5de60faedff 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1175,7 +1175,7 @@ retry:
 	}
 
 	drm_atomic_set_crtc_for_plane(plane_state, crtc);
-	plane_state->fb = fb;
+	drm_atomic_set_fb_for_plane(plane_state, fb);
 	plane_state->crtc_x = crtc_x;
 	plane_state->crtc_y = crtc_y;
 	plane_state->crtc_h = crtc_h;
@@ -1242,7 +1242,7 @@ retry:
 	}
 
 	drm_atomic_set_crtc_for_plane(plane_state, NULL);
-	plane_state->fb = NULL;
+	drm_atomic_set_fb_for_plane(plane_state, NULL);
 	plane_state->crtc_x = 0;
 	plane_state->crtc_y = 0;
 	plane_state->crtc_h = 0;
@@ -1402,7 +1402,7 @@ retry:
 	}
 
 	drm_atomic_set_crtc_for_plane(primary_state, crtc);
-	primary_state->fb = set->fb;
+	drm_atomic_set_fb_for_plane(primary_state, set->fb);
 	primary_state->crtc_x = 0;
 	primary_state->crtc_y = 0;
 	primary_state->crtc_h = set->mode->vdisplay;
@@ -1695,7 +1695,7 @@ retry:
 	}
 
 	drm_atomic_set_crtc_for_plane(plane_state, crtc);
-	plane_state->fb = fb;
+	drm_atomic_set_fb_for_plane(plane_state, fb);
 
 	ret = drm_atomic_async_commit(state);
 	if (ret == -EDEADLK)
@@ -1809,6 +1809,9 @@ EXPORT_SYMBOL(drm_atomic_helper_crtc_destroy_state);
  */
 void drm_atomic_helper_plane_reset(struct drm_plane *plane)
 {
+	if (plane->state && plane->state->fb)
+		drm_framebuffer_unreference(plane->state->fb);
+
 	kfree(plane->state);
 	plane->state = kzalloc(sizeof(*plane->state), GFP_KERNEL);
 }
@@ -1824,10 +1827,17 @@ EXPORT_SYMBOL(drm_atomic_helper_plane_reset);
 struct drm_plane_state *
 drm_atomic_helper_plane_duplicate_state(struct drm_plane *plane)
 {
+	struct drm_plane_state *state;
+
 	if (WARN_ON(!plane->state))
 		return NULL;
 
-	return kmemdup(plane->state, sizeof(*plane->state), GFP_KERNEL);
+	state = kmemdup(plane->state, sizeof(*plane->state), GFP_KERNEL);
+
+	if (state && state->fb)
+		drm_framebuffer_reference(state->fb);
+
+	return state;
 }
 EXPORT_SYMBOL(drm_atomic_helper_plane_duplicate_state);
 
@@ -1840,8 +1850,11 @@ EXPORT_SYMBOL(drm_atomic_helper_plane_duplicate_state);
  * subclassed plane state structure.
  */
 void drm_atomic_helper_plane_destroy_state(struct drm_plane *plane,
-					  struct drm_plane_state *state)
+					   struct drm_plane_state *state)
 {
+	if (state->fb)
+		drm_framebuffer_unreference(state->fb);
+
 	kfree(state);
 }
 EXPORT_SYMBOL(drm_atomic_helper_plane_destroy_state);
diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
index 33195e9adaab..d552708409de 100644
--- a/drivers/gpu/drm/drm_crtc_helper.c
+++ b/drivers/gpu/drm/drm_crtc_helper.c
@@ -34,11 +34,13 @@
 #include <linux/moduleparam.h>
 
 #include <drm/drmP.h>
+#include <drm/drm_atomic.h>
 #include <drm/drm_crtc.h>
 #include <drm/drm_fourcc.h>
 #include <drm/drm_crtc_helper.h>
 #include <drm/drm_fb_helper.h>
 #include <drm/drm_plane_helper.h>
+#include <drm/drm_atomic_helper.h>
 #include <drm/drm_edid.h>
 
 /**
@@ -998,15 +1000,14 @@ int drm_helper_crtc_mode_set_base(struct drm_crtc *crtc, int x, int y,
 	if (plane->funcs->atomic_duplicate_state)
 		plane_state = plane->funcs->atomic_duplicate_state(plane);
 	else if (plane->state)
-		plane_state = kmemdup(plane->state, sizeof(*plane_state),
-				      GFP_KERNEL);
+		plane_state = drm_atomic_helper_plane_duplicate_state(plane);
 	else
 		plane_state = kzalloc(sizeof(*plane_state), GFP_KERNEL);
 	if (!plane_state)
 		return -ENOMEM;
 
 	plane_state->crtc = crtc;
-	plane_state->fb = crtc->primary->fb;
+	drm_atomic_set_fb_for_plane(plane_state, crtc->primary->fb);
 	plane_state->crtc_x = 0;
 	plane_state->crtc_y = 0;
 	plane_state->crtc_h = crtc->mode.vdisplay;
diff --git a/drivers/gpu/drm/drm_plane_helper.c b/drivers/gpu/drm/drm_plane_helper.c
index df69522b1f0e..497104df112b 100644
--- a/drivers/gpu/drm/drm_plane_helper.c
+++ b/drivers/gpu/drm/drm_plane_helper.c
@@ -27,7 +27,9 @@
 #include <drm/drmP.h>
 #include <drm/drm_plane_helper.h>
 #include <drm/drm_rect.h>
+#include <drm/drm_atomic.h>
 #include <drm/drm_crtc_helper.h>
+#include <drm/drm_atomic_helper.h>
 
 #define SUBPIXEL_MASK 0xffff
 
@@ -462,7 +464,7 @@ fail:
 		if (plane->funcs->atomic_destroy_state)
 			plane->funcs->atomic_destroy_state(plane, plane_state);
 		else
-			kfree(plane_state);
+			drm_atomic_helper_plane_destroy_state(plane, plane_state);
 	}
 
 	return ret;
@@ -503,15 +505,14 @@ int drm_plane_helper_update(struct drm_plane *plane, struct drm_crtc *crtc,
 	if (plane->funcs->atomic_duplicate_state)
 		plane_state = plane->funcs->atomic_duplicate_state(plane);
 	else if (plane->state)
-		plane_state = kmemdup(plane->state, sizeof(*plane_state),
-				      GFP_KERNEL);
+		plane_state = drm_atomic_helper_plane_duplicate_state(plane);
 	else
 		plane_state = kzalloc(sizeof(*plane_state), GFP_KERNEL);
 	if (!plane_state)
 		return -ENOMEM;
 
 	plane_state->crtc = crtc;
-	plane_state->fb = fb;
+	drm_atomic_set_fb_for_plane(plane_state, fb);
 	plane_state->crtc_x = crtc_x;
 	plane_state->crtc_y = crtc_y;
 	plane_state->crtc_h = crtc_h;
@@ -550,15 +551,14 @@ int drm_plane_helper_disable(struct drm_plane *plane)
 	if (plane->funcs->atomic_duplicate_state)
 		plane_state = plane->funcs->atomic_duplicate_state(plane);
 	else if (plane->state)
-		plane_state = kmemdup(plane->state, sizeof(*plane_state),
-				      GFP_KERNEL);
+		plane_state = drm_atomic_helper_plane_duplicate_state(plane);
 	else
 		plane_state = kzalloc(sizeof(*plane_state), GFP_KERNEL);
 	if (!plane_state)
 		return -ENOMEM;
 
 	plane_state->crtc = NULL;
-	plane_state->fb = NULL;
+	drm_atomic_set_fb_for_plane(plane_state, NULL);
 
 	return drm_plane_helper_commit(plane, plane_state, plane->fb);
 }
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index 753812034e71..52d92981209f 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -45,6 +45,8 @@ drm_atomic_get_connector_state(struct drm_atomic_state *state,
 
 int drm_atomic_set_crtc_for_plane(struct drm_plane_state *plane_state,
 				  struct drm_crtc *crtc);
+void drm_atomic_set_fb_for_plane(struct drm_plane_state *plane_state,
+				 struct drm_framebuffer *fb);
 int drm_atomic_set_crtc_for_connector(struct drm_connector_state *conn_state,
 				      struct drm_crtc *crtc);
 int
-- 
2.1.1

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