[PATCH 5.1 69/70] drm/amd: fix fb references in async update

[Greg Kroah-Hartman]

From: Helen Koike <helen.koike@xxxxxxxxxxxxx>

commit 332af874db929f92931727bfe191b2c666438c81 upstream.

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

Calling drm_atomic_set_fb_for_plane() (which gets a reference of the new
fb and put the old fb) is not required, as it's taken care by
drm_mode_cursor_universal() when calling drm_atomic_helper_update_plane().

Cc: <stable@xxxxxxxxxxxxxxx> # v4.20+
Fixes: 674e78acae0d ("drm/amd/display: Add fast path for cursor plane updates")
Suggested-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
Signed-off-by: Helen Koike <helen.koike@xxxxxxxxxxxxx>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@xxxxxxx>
Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20190603165610.24614-3-helen.koike@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -3789,8 +3789,7 @@ static void dm_plane_atomic_async_update
 	struct drm_plane_state *old_state =
 		drm_atomic_get_old_plane_state(new_state->state, plane);
 
-	if (plane->state->fb != new_state->fb)
-		drm_atomic_set_fb_for_plane(plane->state, new_state->fb);
+	swap(plane->state->fb, new_state->fb);
 
 	plane->state->src_x = new_state->src_x;
 	plane->state->src_y = new_state->src_y;