[PATCH 4/5] drm/msm: fix fb references in async update

[Helen Koike]

Async update callbacks are expected to set the old_fb in the new_state
so prepare/cleanup framebuffers are balanced.

Cc: <stable at vger.kernel.org> # v4.14+: 25dc194b34dd: drm: Block fb changes for async plane updates
Cc: <stable at vger.kernel.org> # v4.14+: 8105bbaf9afd: drm: don't block fb changes for async plane updates
Fixes: 25dc194b34dd ("drm: Block fb changes for async plane updates")
Suggested-by: Boris Brezillon <boris.brezillon at collabora.com>
Signed-off-by: Helen Koike <helen.koike at collabora.com>

---
Hello,

As mentioned in the cover letter,
I tested on the rockchip and on i915 using igt plane_cursor_legacy and
kms_cursor_legacy and I didn't see any regressions.
But I couldn't test on MSM because I don't have the hardware and I would
appreciate if anyone could test it.

In other platforms (VC4, AMD, Rockchip), there is a hidden
drm_framebuffer_get(new_fb)/drm_framebuffer_put(old_fb) in async_update
that is wrong, but I couldn't identify those here, not sure if it is hidden
somewhere else, but if tests fail this is probably the cause.

Thanks!
Helen

 drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
index be13140967b4..b854f471e9e5 100644
--- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
+++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_plane.c
@@ -502,6 +502,8 @@ static int mdp5_plane_atomic_async_check(struct drm_plane *plane,
 static void mdp5_plane_atomic_async_update(struct drm_plane *plane,
 					   struct drm_plane_state *new_state)
 {
+	struct drm_framebuffer *old_fb = plane->state->fb;
+
 	plane->state->src_x = new_state->src_x;
 	plane->state->src_y = new_state->src_y;
 	plane->state->crtc_x = new_state->crtc_x;
@@ -524,6 +526,8 @@ static void mdp5_plane_atomic_async_update(struct drm_plane *plane,
 
 	*to_mdp5_plane_state(plane->state) =
 		*to_mdp5_plane_state(new_state);
+
+	new_state->fb = old_fb;
 }
 
 static const struct drm_plane_helper_funcs mdp5_plane_helper_funcs = {
-- 
2.20.1