drm/client: Look for command-line modes first

When picking a mode, first look for modes that have been specified
by the user on the kernel's command line. Only if that fails, use
the existing heuristic of picking a nearby mode from it's various
parameters.
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/20220511183125.14294-3-tzimmermann@suse.de

drivers/gpu/drm/drm_client_modeset.c

@@ -165,6 +165,17 @@ drm_connector_pick_cmdline_mode(struct drm_connector *connector)
 	struct drm_display_mode *mode;
 	bool prefer_non_interlace;
 
+	/*
+	 * Find a user-defined mode. If the user gave us a valid
+	 * mode on the kernel command line, it will show up in this
+	 * list.
+	 */
+
+	list_for_each_entry(mode, &connector->modes, head) {
+		if (mode->type & DRM_MODE_TYPE_USERDEF)
+			return mode;
+	}
+
 	cmdline_mode = &connector->cmdline_mode;
 	if (cmdline_mode->specified == false)
 		return NULL;