drm/vc4: crtc: Move the BO handling out of common page-flip callback

We'll soon introduce another completion callback source that won't need
to use the BO reference counting, so let's move it around to create a
function we will be able to share between both callbacks.
Reviewed-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20220610115149.964394-11-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_crtc.c

@@ -802,21 +802,8 @@ vc4_async_page_flip_complete(struct vc4_async_flip_state *flip_state)
 	drm_crtc_vblank_put(crtc);
 	drm_framebuffer_put(flip_state->fb);
 
-	/* Decrement the BO usecnt in order to keep the inc/dec calls balanced
-	 * when the planes are updated through the async update path.
-	 * FIXME: we should move to generic async-page-flip when it's
-	 * available, so that we can get rid of this hand-made cleanup_fb()
-	 * logic.
-	 */
-	if (flip_state->old_fb) {
-		struct drm_gem_cma_object *cma_bo;
-		struct vc4_bo *bo;
-
-		cma_bo = drm_fb_cma_get_gem_obj(flip_state->old_fb, 0);
-		bo = to_vc4_bo(&cma_bo->base);
-		vc4_bo_dec_usecnt(bo);
+	if (flip_state->old_fb)
 		drm_framebuffer_put(flip_state->old_fb);
-	}
 
 	kfree(flip_state);
 }
@@ -825,8 +812,27 @@ static void vc4_async_page_flip_seqno_complete(struct vc4_seqno_cb *cb)
 {
 	struct vc4_async_flip_state *flip_state =
 		container_of(cb, struct vc4_async_flip_state, cb.seqno);
+	struct vc4_bo *bo = NULL;
+
+	if (flip_state->old_fb) {
+		struct drm_gem_cma_object *cma_bo =
+			drm_fb_cma_get_gem_obj(flip_state->old_fb, 0);
+		bo = to_vc4_bo(&cma_bo->base);
+	}
 
 	vc4_async_page_flip_complete(flip_state);
+
+	/*
+	 * Decrement the BO usecnt in order to keep the inc/dec
+	 * calls balanced when the planes are updated through
+	 * the async update path.
+	 *
+	 * FIXME: we should move to generic async-page-flip when
+	 * it's available, so that we can get rid of this
+	 * hand-made cleanup_fb() logic.
+	 */
+	if (bo)
+		vc4_bo_dec_usecnt(bo);
 }
 
 /* Implements async (non-vblank-synced) page flips.