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>

1 files changed, 4 insertions, 3 deletions

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;