drm/mgag200: Implement connector's get_modes with helper

Provide drm_connector_helper_get_modes_from_ddc() to implement the
connector's get_modes callback. The new helper updates the connector
from DDC-provided EDID data.

v2:
	* clear property if EDID is NULL in helper
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Tested-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220516134343.6085-4-tzimmermann@suse.de

drivers/gpu/drm/drm_probe_helper.c

@@ -964,3 +964,39 @@ bool drm_helper_hpd_irq_event(struct drm_device *dev)
 	return changed;
 }
 EXPORT_SYMBOL(drm_helper_hpd_irq_event);
+
+/**
+ * drm_connector_helper_get_modes_from_ddc - Updates the connector's EDID
+ *                                           property from the connector's
+ *                                           DDC channel
+ * @connector: The connector
+ *
+ * Returns:
+ * The number of detected display modes.
+ *
+ * Uses a connector's DDC channel to retrieve EDID data and update the
+ * connector's EDID property and display modes. Drivers can use this
+ * function to implement struct &drm_connector_helper_funcs.get_modes
+ * for connectors with a DDC channel.
+ */
+int drm_connector_helper_get_modes_from_ddc(struct drm_connector *connector)
+{
+	struct edid *edid;
+	int count = 0;
+
+	if (!connector->ddc)
+		return 0;
+
+	edid = drm_get_edid(connector, connector->ddc);
+
+	// clears property if EDID is NULL
+	drm_connector_update_edid_property(connector, edid);
+
+	if (edid) {
+		count = drm_add_edid_modes(connector, edid);
+		kfree(edid);
+	}
+
+	return count;
+}
+EXPORT_SYMBOL(drm_connector_helper_get_modes_from_ddc);

drivers/gpu/drm/mgag200/mgag200_mode.c

@@ -689,26 +689,17 @@ static void mgag200_disable_display(struct mga_device *mdev)
  * Connector
  */
 
-static int mga_vga_get_modes(struct drm_connector *connector)
+static int mgag200_vga_connector_helper_get_modes(struct drm_connector *connector)
 {
 	struct mga_device *mdev = to_mga_device(connector->dev);
-	struct mga_connector *mga_connector = to_mga_connector(connector);
-	struct edid *edid;
-	int ret = 0;
+	int ret;
 
 	/*
 	 * Protect access to I/O registers from concurrent modesetting
 	 * by acquiring the I/O-register lock.
 	 */
 	mutex_lock(&mdev->rmmio_lock);
-
-	edid = drm_get_edid(connector, &mga_connector->i2c->adapter);
-	if (edid) {
-		drm_connector_update_edid_property(connector, edid);
-		ret = drm_add_edid_modes(connector, edid);
-		kfree(edid);
-	}
-
+	ret = drm_connector_helper_get_modes_from_ddc(connector);
 	mutex_unlock(&mdev->rmmio_lock);
 
 	return ret;
@@ -828,7 +819,7 @@ static void mga_connector_destroy(struct drm_connector *connector)
 }
 
 static const struct drm_connector_helper_funcs mga_vga_connector_helper_funcs = {
-	.get_modes  = mga_vga_get_modes,
+	.get_modes  = mgag200_vga_connector_helper_get_modes,
 	.mode_valid = mga_vga_mode_valid,
 };
 

include/drm/drm_probe_helper.h

@@ -26,4 +26,6 @@ void drm_kms_helper_poll_disable(struct drm_device *dev);
 void drm_kms_helper_poll_enable(struct drm_device *dev);
 bool drm_kms_helper_is_poll_worker(void);
 
+int drm_connector_helper_get_modes_from_ddc(struct drm_connector *connector);
+
 #endif