drm/vc4: crtc: Use an union to store the page flip callback

We'll need to extend the vc4_async_flip_state structure to rely on
another callback implementation, so let's move the current one into a
union.
Reviewed-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20220610115149.964394-10-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_crtc.c

@@ -775,17 +775,17 @@ struct vc4_async_flip_state {
 	struct drm_framebuffer *old_fb;
 	struct drm_pending_vblank_event *event;
 
-	struct vc4_seqno_cb cb;
+	union {
+		struct vc4_seqno_cb seqno;
+	} cb;
 };
 
 /* Called when the V3D execution for the BO being flipped to is done, so that
  * we can actually update the plane's address to point to it.
  */
 static void
-vc4_async_page_flip_complete(struct vc4_seqno_cb *cb)
+vc4_async_page_flip_complete(struct vc4_async_flip_state *flip_state)
 {
-	struct vc4_async_flip_state *flip_state =
-		container_of(cb, struct vc4_async_flip_state, cb);
 	struct drm_crtc *crtc = flip_state->crtc;
 	struct drm_device *dev = crtc->dev;
 	struct drm_plane *plane = crtc->primary;
@@ -821,6 +821,14 @@ vc4_async_page_flip_complete(struct vc4_seqno_cb *cb)
 	kfree(flip_state);
 }
 
+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);
+
+	vc4_async_page_flip_complete(flip_state);
+}
+
 /* Implements async (non-vblank-synced) page flips.
  *
  * The page flip ioctl needs to return immediately, so we grab the
@@ -881,8 +889,8 @@ static int vc4_async_page_flip(struct drm_crtc *crtc,
 	 */
 	drm_atomic_set_fb_for_plane(plane->state, fb);
 
-	vc4_queue_seqno_cb(dev, &flip_state->cb, bo->seqno,
-			   vc4_async_page_flip_complete);
+	vc4_queue_seqno_cb(dev, &flip_state->cb.seqno, bo->seqno,
+			   vc4_async_page_flip_seqno_complete);
 
 	/* Driver takes ownership of state on successful async commit. */
 	return 0;