drm/amd/display: Relax requirements for CRTCs to be enabled

[Why]
As long as we have at least one non-cursor plane enabled on a CRTC then
the CRTC itself can remain enabled.

This will allow for commits where there's an overlay plane enabled but
no primary plane enabled.

[How]
Remove existing primary plane fb != NULL checks and replace them with
the new does_crtc_have_active_plane helper.

This will be called from atomic check when validating the CRTC.

Since the primary plane state can now potentially be NULL we'll need
to guard for that when accessing it in some of the cursor logic.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: David Francis <David.Francis@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -3862,6 +3862,38 @@ static void dm_crtc_helper_disable(struct drm_crtc *crtc)
 {
 }
 
+static bool does_crtc_have_active_plane(struct drm_crtc_state *new_crtc_state)
+{
+	struct drm_atomic_state *state = new_crtc_state->state;
+	struct drm_plane *plane;
+	int num_active = 0;
+
+	drm_for_each_plane_mask(plane, state->dev, new_crtc_state->plane_mask) {
+		struct drm_plane_state *new_plane_state;
+
+		/* Cursor planes are "fake". */
+		if (plane->type == DRM_PLANE_TYPE_CURSOR)
+			continue;
+
+		new_plane_state = drm_atomic_get_new_plane_state(state, plane);
+
+		if (!new_plane_state) {
+			/*
+			 * The plane is enable on the CRTC and hasn't changed
+			 * state. This means that it previously passed
+			 * validation and is therefore enabled.
+			 */
+			num_active += 1;
+			continue;
+		}
+
+		/* We need a framebuffer to be considered enabled. */
+		num_active += (new_plane_state->fb != NULL);
+	}
+
+	return num_active > 0;
+}
+
 static int dm_crtc_helper_atomic_check(struct drm_crtc *crtc,
 				       struct drm_crtc_state *state)
 {
@@ -3880,6 +3912,11 @@ static int dm_crtc_helper_atomic_check(struct drm_crtc *crtc,
 	if (!dm_crtc_state->stream)
 		return 0;
 
+	/* We want at least one hardware plane enabled to use the stream. */
+	if (state->enable && state->active &&
+	    !does_crtc_have_active_plane(state))
+		return -EINVAL;
+
 	if (dc_validate_stream(dc, dm_crtc_state->stream) == DC_OK)
 		return 0;
 
@@ -4849,9 +4886,13 @@ static int get_cursor_position(struct drm_plane *plane, struct drm_crtc *crtc,
 
 	x = plane->state->crtc_x;
 	y = plane->state->crtc_y;
-	/* avivo cursor are offset into the total surface */
-	x += crtc->primary->state->src_x >> 16;
-	y += crtc->primary->state->src_y >> 16;
+
+	if (crtc->primary->state) {
+		/* avivo cursor are offset into the total surface */
+		x += crtc->primary->state->src_x >> 16;
+		y += crtc->primary->state->src_y >> 16;
+	}
+
 	if (x < 0) {
 		xorigin = min(-x, amdgpu_crtc->max_cursor_width - 1);
 		x = 0;
@@ -5872,21 +5913,12 @@ static int dm_update_crtc_state(struct amdgpu_display_manager *dm,
 	struct amdgpu_dm_connector *aconnector = NULL;
 	struct drm_connector_state *drm_new_conn_state = NULL, *drm_old_conn_state = NULL;
 	struct dm_connector_state *dm_new_conn_state = NULL, *dm_old_conn_state = NULL;
-	struct drm_plane_state *new_plane_state = NULL;
 
 	new_stream = NULL;
 
 	dm_old_crtc_state = to_dm_crtc_state(old_crtc_state);
 	dm_new_crtc_state = to_dm_crtc_state(new_crtc_state);
 	acrtc = to_amdgpu_crtc(crtc);
-
-	new_plane_state = drm_atomic_get_new_plane_state(state, new_crtc_state->crtc->primary);
-
-	if (new_crtc_state->enable && new_plane_state && !new_plane_state->fb) {
-		ret = -EINVAL;
-		goto fail;
-	}
-
 	aconnector = amdgpu_dm_find_first_crtc_matching_connector(state, crtc);
 
 	/* TODO This hack should go away */