drm/atomic: Refcounting for plane_state->fb

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 references.

- 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 can't 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.

v2: Update kerneldoc - copypasta fail.

v3: Fix spelling in the commit message (Sean).

Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index ad15a88..ed991ba 100644 (file)
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -367,6 +367,34 @@ 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 framebuffer for a plane requires us to grab a reference
+ * to the new fb and drop the reference to the old fb, if there is one. 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

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 2b1db0c..ca839bd 100644 (file)
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1182,7 +1182,7 @@ retry:
        ret = drm_atomic_set_crtc_for_plane(plane_state, crtc);
        if (ret != 0)
                goto fail;
-       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;
@@ -1250,7 +1250,7 @@ retry:
        ret = drm_atomic_set_crtc_for_plane(plane_state, NULL);
        if (ret != 0)
                goto fail;
-       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;
@@ -1422,7 +1422,7 @@ retry:
        ret = drm_atomic_set_crtc_for_plane(primary_state, crtc);
        if (ret != 0)
                goto fail;
-       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;
@@ -1694,7 +1694,7 @@ retry:
        ret = drm_atomic_set_crtc_for_plane(plane_state, crtc);
        if (ret != 0)
                goto fail;
-       plane_state->fb = fb;
+       drm_atomic_set_fb_for_plane(plane_state, fb);
 
        ret = drm_atomic_async_commit(state);
        if (ret != 0)
@@ -1808,6 +1808,9 @@ 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);
 }
@@ -1823,10 +1826,17 @@ 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);
 
@@ -1839,8 +1849,11 @@ 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 --cc drivers/gpu/drm/drm_crtc_helper.c
Simple merge

diff --cc drivers/gpu/drm/drm_plane_helper.c
Simple merge

diff --cc include/drm/drm_atomic.h
Simple merge