drm: add drm_set_preferred_mode

New helper function to set the preferred video mode.  Can be called
after drm_add_modes_noedid if you don't want the largest supported
video mode be used by default.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_edid.c

@@ -3482,6 +3482,19 @@ int drm_add_modes_noedid(struct drm_connector *connector,
 }
 EXPORT_SYMBOL(drm_add_modes_noedid);
 
+void drm_set_preferred_mode(struct drm_connector *connector,
+			   int hpref, int vpref)
+{
+	struct drm_display_mode *mode;
+
+	list_for_each_entry(mode, &connector->probed_modes, head) {
+		if (drm_mode_width(mode)  == hpref &&
+		    drm_mode_height(mode) == vpref)
+			mode->type |= DRM_MODE_TYPE_PREFERRED;
+	}
+}
+EXPORT_SYMBOL(drm_set_preferred_mode);
+
 /**
  * drm_hdmi_avi_infoframe_from_display_mode() - fill an HDMI AVI infoframe with
  *                                              data from a DRM display mode

include/drm/drm_crtc.h

@@ -1118,6 +1118,8 @@ extern struct drm_display_mode *drm_gtf_mode_complex(struct drm_device *dev,
 				int GTF_2C, int GTF_K, int GTF_2J);
 extern int drm_add_modes_noedid(struct drm_connector *connector,
 				int hdisplay, int vdisplay);
+extern void drm_set_preferred_mode(struct drm_connector *connector,
+				   int hpref, int vpref);
 
 extern int drm_edid_header_is_valid(const u8 *raw_edid);
 extern bool drm_edid_block_valid(u8 *raw_edid, int block, bool print_bad_edid);