[PATCH v6 07/16] drm/bridge: synopsys: dw-dp: Add follow-up bridge support

[Sebastian Reichel]

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

It's fine to fatally error out when there is no follow-up bridge
as the Rockchip Designware Displayport controller is the only
user of the bridge helper and has the port marked as required
in its binding.

Signed-off-by: Sebastian Reichel <sebastian.reichel@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/bridge/synopsys/dw-dp.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-dp.c b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
index 259efc25b56e..591b75c4cc36 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-dp.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
@@ -329,6 +329,8 @@ struct dw_dp {
 	struct dw_dp_plat_data plat_data;
 	u8 pixel_mode;
 
+	struct drm_bridge *next_bridge;
+
 	DECLARE_BITMAP(sdp_reg_bank, SDP_REG_BANK_SIZE);
 };
 
@@ -2021,18 +2023,35 @@ int dw_dp_bind(struct dw_dp *dp, struct drm_encoder *encoder)
 		goto unregister_aux;
 	}
 
+	dp->next_bridge = of_drm_get_bridge_by_endpoint(dev->of_node, 1, 0);
+	if (IS_ERR(dp->next_bridge)) {
+		ret = PTR_ERR(dp->next_bridge);
+		dev_err_probe(dev, ret, "failed to get follow-up bridge.\n");
+		goto unregister_aux;
+	}
+
+	ret = drm_bridge_attach(encoder, dp->next_bridge, bridge,
+				DRM_BRIDGE_ATTACH_NO_CONNECTOR);
+	if (ret) {
+		dev_err_probe(dev, ret, "Failed to attach next bridge\n");
+		goto put_next_bridge;
+	}
+
 	dw_dp_init_hw(dp);
 
 	ret = phy_init(dp->phy);
 	if (ret) {
 		dev_err_probe(dev, ret, "phy init failed\n");
-		goto unregister_aux;
+		goto put_next_bridge;
 	}
 
 	enable_irq(dp->irq);
 
 	return 0;
 
+put_next_bridge:
+	drm_bridge_put(dp->next_bridge);
+
 unregister_aux:
 	drm_dp_aux_unregister(&dp->aux);
 
@@ -2048,6 +2067,7 @@ void dw_dp_unbind(struct dw_dp *dp)
 	disable_irq(dp->irq);
 	cancel_work_sync(&dp->hpd_work);
 	phy_exit(dp->phy);
+	drm_bridge_put(dp->next_bridge);
 	drm_dp_aux_unregister(&dp->aux);
 	drm_bridge_remove(&dp->bridge);
 }

-- 
2.53.0