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

1 files changed, 36 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
index 682359512996..d77f17867195 100644
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/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);