drm/vmwgfx: Trigger a modeset when the screen moves

When multi-monitor is cycled the X,Y position of the Screen Target will
likely change but the resolution will not. We need to trigger a modeset
when this occurs in order to recreate the Screen Target with the correct
X,Y position.

Fixes a bug where multiple displays are shown in a single scrollable
host window rather than in 2+ windows on separate host displays.

Fixes: 42682693 ("drm/vmwgfx: Filter modes which exceed graphics memory")
Signed-off-by: Ian Forbes <ian.forbes@broadcom.com>
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240624205951.23343-1-ian.forbes@broadcom.com

drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c

@@ -873,6 +873,32 @@ vmw_stdu_connector_mode_valid(struct drm_connector *connector,
 	return MODE_OK;
 }
 
+/*
+ * Trigger a modeset if the X,Y position of the Screen Target changes.
+ * This is needed when multi-mon is cycled. The original Screen Target will have
+ * the same mode but its relative X,Y position in the topology will change.
+ */
+static int vmw_stdu_connector_atomic_check(struct drm_connector *conn,
+					   struct drm_atomic_state *state)
+{
+	struct drm_connector_state *conn_state;
+	struct vmw_screen_target_display_unit *du;
+	struct drm_crtc_state *new_crtc_state;
+
+	conn_state = drm_atomic_get_connector_state(state, conn);
+	du = vmw_connector_to_stdu(conn);
+
+	if (!conn_state->crtc)
+		return 0;
+
+	new_crtc_state = drm_atomic_get_new_crtc_state(state, conn_state->crtc);
+	if (du->base.gui_x != du->base.set_gui_x ||
+	    du->base.gui_y != du->base.set_gui_y)
+		new_crtc_state->mode_changed = true;
+
+	return 0;
+}
+
 static const struct drm_connector_funcs vmw_stdu_connector_funcs = {
 	.dpms = vmw_du_connector_dpms,
 	.detect = vmw_du_connector_detect,
@@ -887,7 +913,8 @@ static const struct drm_connector_funcs vmw_stdu_connector_funcs = {
 static const struct
 drm_connector_helper_funcs vmw_stdu_connector_helper_funcs = {
 	.get_modes = vmw_connector_get_modes,
-	.mode_valid = vmw_stdu_connector_mode_valid
+	.mode_valid = vmw_stdu_connector_mode_valid,
+	.atomic_check = vmw_stdu_connector_atomic_check,
 };