[PATCH 2/5] drm/rockchip: fix fb references in async update

[Helen Koike]

In the case of async update, modifications are done in place, i.e. in the
current plane state, so the new_state is prepared and the new_state is
cleanup up (instead of the old_state, diferrently on what happen in a
normal sync update).
To cleanup the old_fb properly, it needs to be placed in the new_state
in the end of async_update, so cleanup call will unreference the old_fb
correctly.

Also, the previous code had a:

	plane_state = plane->funcs->atomic_duplicate_state(plane);
	...
	swap(plane_state, plane->state);

	if (plane->state->fb && plane->state->fb != new_state->fb) {
	...
	}

Which was wrong, as the fb were just assigned to be equal, so this if
statement nevers evaluates to true.

Another details is that the function drm_crtc_vblank_get() can only be
called when vop->is_enabled is true, otherwise it has no effect and
trows a WARN_ON().

Calling drm_atomic_set_fb_for_plane() (which get a referent of the new
fb and pus the old fb) is not required, as it is taken care by
drm_mode_cursor_universal() when calling
drm_atomic_helper_update_plane().

Signed-off-by: Helen Koike <helen.koike@xxxxxxxxxxxxx>

---
Hello,

I tested on the rockchip ficus v1.1 using igt plane_cursor_legacy and
kms_cursor_legacy and I didn't see any regressions.

It was me who worked on the first version and I am really sorry about that
dead code in the if statement.
Now I understand drm better and I know better how to properly test things with
more care/details.

Also, I didn't CC to stable here as I saw the async_update function was only
added on v4.20, please let me know if I should CC to stable.

Thanks!
Helen

 drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 42 ++++++++++++---------
 1 file changed, 24 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
index c7d4c6073ea5..a1ee8c156a7b 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
@@ -912,30 +912,31 @@ static void vop_plane_atomic_async_update(struct drm_plane *plane,
 					  struct drm_plane_state *new_state)
 {
 	struct vop *vop = to_vop(plane->state->crtc);
-	struct drm_plane_state *plane_state;
+	struct drm_framebuffer *old_fb = plane->state->fb;
 
-	plane_state = plane->funcs->atomic_duplicate_state(plane);
-	plane_state->crtc_x = new_state->crtc_x;
-	plane_state->crtc_y = new_state->crtc_y;
-	plane_state->crtc_h = new_state->crtc_h;
-	plane_state->crtc_w = new_state->crtc_w;
-	plane_state->src_x = new_state->src_x;
-	plane_state->src_y = new_state->src_y;
-	plane_state->src_h = new_state->src_h;
-	plane_state->src_w = new_state->src_w;
-
-	if (plane_state->fb != new_state->fb)
-		drm_atomic_set_fb_for_plane(plane_state, new_state->fb);
-
-	swap(plane_state, plane->state);
-
-	if (plane->state->fb && plane->state->fb != new_state->fb) {
+	/*
+	 * A scanout can still be occurring, so we can't drop the reference to
+	 * the old framebuffer. To solve this we get a reference to old_fb and
+	 * set a worker to release it later.
+	 */
+	if (vop->is_enabled &&
+	    plane->state->fb && plane->state->fb != new_state->fb) {
 		drm_framebuffer_get(plane->state->fb);
 		WARN_ON(drm_crtc_vblank_get(plane->state->crtc) != 0);
 		drm_flip_work_queue(&vop->fb_unref_work, plane->state->fb);
 		set_bit(VOP_PENDING_FB_UNREF, &vop->pending);
 	}
 
+	plane->state->crtc_x = new_state->crtc_x;
+	plane->state->crtc_y = new_state->crtc_y;
+	plane->state->crtc_h = new_state->crtc_h;
+	plane->state->crtc_w = new_state->crtc_w;
+	plane->state->src_x = new_state->src_x;
+	plane->state->src_y = new_state->src_y;
+	plane->state->src_h = new_state->src_h;
+	plane->state->src_w = new_state->src_w;
+	plane->state->fb = new_state->fb;
+
 	if (vop->is_enabled) {
 		rockchip_drm_psr_inhibit_get_state(new_state->state);
 		vop_plane_atomic_update(plane, plane->state);
@@ -945,7 +946,12 @@ static void vop_plane_atomic_async_update(struct drm_plane *plane,
 		rockchip_drm_psr_inhibit_put_state(new_state->state);
 	}
 
-	plane->funcs->atomic_destroy_state(plane, plane_state);
+	/*
+	 * In async update we perform inplace modifications and release the
+	 * new_state. The following is required so we release the reference of
+	 * the old framebuffer.
+	 */
+	new_state->fb = old_fb;
 }
 
 static const struct drm_plane_helper_funcs plane_helper_funcs = {
-- 
2.20.1