drm/rockchip: fix fb references in async update

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
cleaned up (instead of the old_state, unlike what happens 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().

Fixes: 15609559 ("drm/rockchip: update cursors asynchronously through atomic.")
Cc: <stable@vger.kernel.org> # v4.20+
Signed-off-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190603165610.24614-2-helen.koike@collabora.com

drivers/gpu/drm/rockchip/rockchip_drm_vop.c

@@ -924,29 +924,17 @@ 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;
-
-	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) {
-		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);
-	}
+	struct drm_framebuffer *old_fb = plane->state->fb;
+
+	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;
+	swap(plane->state->fb, new_state->fb);
 
 	if (vop->is_enabled) {
 		rockchip_drm_psr_inhibit_get_state(new_state->state);
@@ -955,9 +943,22 @@ static void vop_plane_atomic_async_update(struct drm_plane *plane,
 		vop_cfg_done(vop);
 		spin_unlock(&vop->reg_lock);
 		rockchip_drm_psr_inhibit_put_state(new_state->state);
-	}
 
-	plane->funcs->atomic_destroy_state(plane, plane_state);
+		/*
+		 * 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.
+		 * FIXME: if we perform 500 async_update calls before the
+		 * vblank, then we can have 500 different framebuffers waiting
+		 * to be released.
+		 */
+		if (old_fb && plane->state->fb != old_fb) {
+			drm_framebuffer_get(old_fb);
+			WARN_ON(drm_crtc_vblank_get(plane->state->crtc) != 0);
+			drm_flip_work_queue(&vop->fb_unref_work, old_fb);
+			set_bit(VOP_PENDING_FB_UNREF, &vop->pending);
+		}
+	}
 }
 
 static const struct drm_plane_helper_funcs plane_helper_funcs = {