[PATCH v2 05/12] drm/bridge: synopsys: dw-dp: Add follow-up bridge support

[Sebastian Reichel <sebastian.reichel@collabora.com>]

Add support to use USB-C connectors with the DP altmode helper code on
devicetree based platforms. To get this working there must be a DRM
bridge chain from the DisplayPort controller to the USB-C connector.
E.g. on Rockchip RK3576:

root@rk3576 # cat /sys/kernel/debug/dri/0/encoder-0/bridges
bridge[0]: dw_dp_bridge_funcs
        refcount: 7
        type: [10] DP
        OF: /soc/dp@27e40000:rockchip,rk3576-dp
        ops: [0x47] detect edid hpd
bridge[1]: drm_aux_bridge_funcs
        refcount: 4
        type: [0] Unknown
        OF: /soc/phy@2b010000:rockchip,rk3576-usbdp-phy
        ops: [0x0]
bridge[2]: drm_aux_hpd_bridge_funcs
        refcount: 5
        type: [10] DP
        OF: /soc/i2c@2ac50000/typec-portc@22/connector:usb-c-connector
        ops: [0x4] hpd

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
---
 drivers/gpu/drm/bridge/synopsys/dw-dp.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-dp.c b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
index fc4ddb7792d7..ccc55e40e81c 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-dp.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
@@ -1970,7 +1970,7 @@ struct dw_dp *dw_dp_bind(struct device *dev, struct drm_encoder *encoder,
 {
 	struct platform_device *pdev = to_platform_device(dev);
 	struct dw_dp *dp;
-	struct drm_bridge *bridge;
+	struct drm_bridge *bridge, *next_bridge;
 	void __iomem *res;
 	int ret;
 
@@ -2064,6 +2064,20 @@ struct dw_dp *dw_dp_bind(struct device *dev, struct drm_encoder *encoder,
 		goto unregister_aux;
 	}
 
+	next_bridge = devm_drm_of_get_bridge(dev, dev->of_node, 1, 0);
+	if (IS_ERR(next_bridge)) {
+		ret = PTR_ERR(next_bridge);
+		dev_err_probe(dev, ret, "failed to get follow-up bridge.\n");
+		goto unregister_aux;
+	}
+
+	ret = drm_bridge_attach(encoder, next_bridge, bridge,
+				DRM_BRIDGE_ATTACH_NO_CONNECTOR);
+	if (ret) {
+		dev_err_probe(dev, ret, "Failed to attach next bridge\n");
+		goto unregister_aux;
+	}
+
 	dw_dp_init_hw(dp);
 
 	ret = phy_init(dp->phy);

-- 
2.53.0