drm/msm/dp: support attaching bridges to the DP encoder

Currently DP driver will allocate panel bridge for eDP panels. This
supports only the following topology:

- eDP encoder ⇒ eDP panel (wrapped using panel-bridge)

Simplify this code to just check if there is any next bridge in the
chain (be it a panel bridge or regular bridge). Rename panel_bridge
field to next_bridge accordingly.

This allows one to use e.g. one of the following display topologies:

- eDP encoder ⇒ ptn3460 ⇒ fixed LVDS panel
- eDP encoder ⇒ ptn3460 ⇒ LVDS connector with EDID lines for panel autodetect
- eDP encoder ⇒ ptn3460 ⇒ THC63LVD1024 ⇒ DPI panel.
- eDP encoder ⇒ LT8912 ⇒ DSI panel

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Tested-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20220211224006.1797846-3-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/dp/dp_display.c

@@ -266,7 +266,7 @@ static int dp_display_bind(struct device *dev, struct device *master,
 		goto end;
 	}
 
-	dp->dp_display.panel_bridge = dp->parser->panel_bridge;
+	dp->dp_display.next_bridge = dp->parser->next_bridge;
 
 	dp->aux->drm_dev = drm;
 	rc = dp_aux_register(dp->aux);

drivers/gpu/drm/msm/dp/dp_display.h

@@ -16,7 +16,7 @@ struct msm_dp {
 	struct drm_bridge *bridge;
 	struct drm_connector *connector;
 	struct drm_encoder *encoder;
-	struct drm_bridge *panel_bridge;
+	struct drm_bridge *next_bridge;
 	bool is_connected;
 	bool audio_enabled;
 	bool power_on;

drivers/gpu/drm/msm/dp/dp_drm.c

@@ -236,9 +236,9 @@ struct drm_bridge *msm_dp_bridge_init(struct msm_dp *dp_display, struct drm_devi
 		return ERR_PTR(rc);
 	}
 
-	if (dp_display->panel_bridge) {
+	if (dp_display->next_bridge) {
 		rc = drm_bridge_attach(dp_display->encoder,
-					dp_display->panel_bridge, bridge,
+					dp_display->next_bridge, bridge,
 					DRM_BRIDGE_ATTACH_NO_CONNECTOR);
 		if (rc < 0) {
 			DRM_ERROR("failed to attach panel bridge: %d\n", rc);

drivers/gpu/drm/msm/dp/dp_parser.c

@@ -265,23 +265,16 @@ static int dp_parser_clock(struct dp_parser *parser)
 	return 0;
 }
 
-static int dp_parser_find_panel(struct dp_parser *parser)
+static int dp_parser_find_next_bridge(struct dp_parser *parser)
 {
 	struct device *dev = &parser->pdev->dev;
-	struct drm_panel *panel;
-	int rc;
+	struct drm_bridge *bridge;
 
-	rc = drm_of_find_panel_or_bridge(dev->of_node, 1, 0, &panel, NULL);
-	if (rc) {
-		DRM_ERROR("failed to acquire DRM panel: %d\n", rc);
-		return rc;
-	}
+	bridge = devm_drm_of_get_bridge(dev, dev->of_node, 1, 0);
+	if (IS_ERR(bridge))
+		return PTR_ERR(bridge);
 
-	parser->panel_bridge = devm_drm_panel_bridge_add(dev, panel);
-	if (IS_ERR(parser->panel_bridge)) {
-		DRM_ERROR("failed to create panel bridge\n");
-		return PTR_ERR(parser->panel_bridge);
-	}
+	parser->next_bridge = bridge;
 
 	return 0;
 }
@@ -307,10 +300,18 @@ static int dp_parser_parse(struct dp_parser *parser, int connector_type)
 	if (rc)
 		return rc;
 
+	/*
+	 * Currently we support external bridges only for eDP connectors.
+	 *
+	 * No external bridges are expected for the DisplayPort connector,
+	 * it is physically present in a form of a DP or USB-C connector.
+	 */
 	if (connector_type == DRM_MODE_CONNECTOR_eDP) {
-		rc = dp_parser_find_panel(parser);
-		if (rc)
+		rc = dp_parser_find_next_bridge(parser);
+		if (rc) {
+			DRM_ERROR("DP: failed to find next bridge\n");
 			return rc;
+		}
 	}
 
 	/* Map the corresponding regulator information according to

drivers/gpu/drm/msm/dp/dp_parser.h

@@ -123,7 +123,7 @@ struct dp_parser {
 	struct dp_display_data disp_data;
 	const struct dp_regulator_cfg *regulator_cfg;
 	u32 max_dp_lanes;
-	struct drm_bridge *panel_bridge;
+	struct drm_bridge *next_bridge;
 
 	int (*parse)(struct dp_parser *parser, int connector_type);
 };