drm: Always warn if user-defined modes are not supported

Print a warning if a user-specifed display mode is not supported by
the display pipeline. Users specified the display mode on the kernel
command line with the use of the video= parameter. Setting an
unsupported mode will leave the console blank, so we should at least
let the user know why.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220511183125.14294-2-tzimmermann@suse.de

drivers/gpu/drm/drm_modes.c

@@ -1328,6 +1328,10 @@ void drm_mode_prune_invalid(struct drm_device *dev,
 	list_for_each_entry_safe(mode, t, mode_list, head) {
 		if (mode->status != MODE_OK) {
 			list_del(&mode->head);
+			if (mode->type & DRM_MODE_TYPE_USERDEF) {
+				drm_warn(dev, "User-defined mode not supported: "
+					 DRM_MODE_FMT "\n", DRM_MODE_ARG(mode));
+			}
 			if (verbose) {
 				drm_mode_debug_printmodeline(mode);
 				DRM_DEBUG_KMS("Not using %s mode: %s\n",