drm/bridge: ti-sn65dsi86: Read EDID blob over DDC

Use the DDC connection to read the EDID from the eDP panel instead of
relying on the panel to tell us the modes.
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Cc: Jonas Karlman <jonas@kwiboo.se>
Cc: Jernej Skrabec <jernej.skrabec@siol.net>
Cc: Sean Paul <seanpaul@chromium.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201102181144.3469197-4-swboyd@chromium.org

drivers/gpu/drm/bridge/ti-sn65dsi86.c

@@ -121,6 +121,7 @@
  * @debugfs:      Used for managing our debugfs.
  * @host_node:    Remote DSI node.
  * @dsi:          Our MIPI DSI source.
+ * @edid:         Detected EDID of eDP panel.
  * @refclk:       Our reference clock.
  * @panel:        Our panel.
  * @enable_gpio:  The GPIO we toggle to enable the bridge.
@@ -146,6 +147,7 @@ struct ti_sn_bridge {
 	struct drm_bridge		bridge;
 	struct drm_connector		connector;
 	struct dentry			*debugfs;
+	struct edid			*edid;
 	struct device_node		*host_node;
 	struct mipi_dsi_device		*dsi;
 	struct clk			*refclk;
@@ -267,6 +269,23 @@ connector_to_ti_sn_bridge(struct drm_connector *connector)
 static int ti_sn_bridge_connector_get_modes(struct drm_connector *connector)
 {
 	struct ti_sn_bridge *pdata = connector_to_ti_sn_bridge(connector);
+	struct edid *edid = pdata->edid;
+	int num, ret;
+
+	if (!edid) {
+		pm_runtime_get_sync(pdata->dev);
+		edid = pdata->edid = drm_get_edid(connector, &pdata->aux.ddc);
+		pm_runtime_put(pdata->dev);
+	}
+
+	if (edid && drm_edid_is_valid(edid)) {
+		ret = drm_connector_update_edid_property(connector, edid);
+		if (!ret) {
+			num = drm_add_edid_modes(connector, edid);
+			if (num)
+				return num;
+		}
+	}
 
 	return drm_panel_get_modes(pdata->panel, connector);
 }
@@ -1262,6 +1281,7 @@ static int ti_sn_bridge_remove(struct i2c_client *client)
 	if (!pdata)
 		return -EINVAL;
 
+	kfree(pdata->edid);
 	ti_sn_debugfs_remove(pdata);
 
 	of_node_put(pdata->host_node);