drm/amd/display: Bail from dm_check_crtc_cursor if no relevant change

If no plane was newly enabled or changed scaling, there can be no new
scaling mismatch with the cursor plane.

By not pulling non-cursor plane states into all atomic commits while
the cursor plane is enabled, this avoids synchronizing all cursor plane
changes to vertical blank, which caused the following IGT tests to fail:

kms_cursor_legacy@cursor-vs-flip.*
kms_cursor_legacy@flip-vs-cursor.*

Fixes: 003048dd ("drm/amd/display: Check all enabled planes in dm_check_crtc_cursor")
Signed-off-by: Michel Dänzer <mdaenzer@redhat.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -10261,10 +10261,12 @@ static int dm_check_crtc_cursor(struct drm_atomic_state *state,
 				struct drm_crtc *crtc,
 				struct drm_crtc_state *new_crtc_state)
 {
-	struct drm_plane *cursor = crtc->cursor, *underlying;
+	struct drm_plane *cursor = crtc->cursor, *plane, *underlying;
+	struct drm_plane_state *old_plane_state, *new_plane_state;
 	struct drm_plane_state *new_cursor_state, *new_underlying_state;
 	int i;
 	int cursor_scale_w, cursor_scale_h, underlying_scale_w, underlying_scale_h;
+	bool any_relevant_change = false;
 
 	/* On DCE and DCN there is no dedicated hardware cursor plane. We get a
 	 * cursor per pipe but it's going to inherit the scaling and
@@ -10272,6 +10274,35 @@ static int dm_check_crtc_cursor(struct drm_atomic_state *state,
 	 * blending properties match the underlying planes'.
 	 */
 
+	/* If no plane was enabled or changed scaling, no need to check again */
+	for_each_oldnew_plane_in_state(state, plane, old_plane_state, new_plane_state, i) {
+		int new_scale_w, new_scale_h, old_scale_w, old_scale_h;
+
+		if (!new_plane_state || !new_plane_state->fb || new_plane_state->crtc != crtc)
+			continue;
+
+		if (!old_plane_state || !old_plane_state->fb || old_plane_state->crtc != crtc) {
+			any_relevant_change = true;
+			break;
+		}
+
+		if (new_plane_state->fb == old_plane_state->fb &&
+		    new_plane_state->crtc_w == old_plane_state->crtc_w &&
+		    new_plane_state->crtc_h == old_plane_state->crtc_h)
+			continue;
+
+		dm_get_plane_scale(new_plane_state, &new_scale_w, &new_scale_h);
+		dm_get_plane_scale(old_plane_state, &old_scale_w, &old_scale_h);
+
+		if (new_scale_w != old_scale_w || new_scale_h != old_scale_h) {
+			any_relevant_change = true;
+			break;
+		}
+	}
+
+	if (!any_relevant_change)
+		return 0;
+
 	new_cursor_state = drm_atomic_get_plane_state(state, cursor);
 	if (IS_ERR(new_cursor_state))
 		return PTR_ERR(new_cursor_state);