[PATCH v10 10/21] drm/bridge: synopsys: dw-dp: Add follow-up bridge support

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 <[email protected]>
---
 drivers/gpu/drm/bridge/synopsys/dw-dp.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-dp.c b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
index 106978544cdf..ce5bf9f107cd 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-dp.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
@@ -330,6 +330,8 @@ 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);
 };
 
@@ -1893,8 +1895,28 @@ static int dw_dp_bridge_attach(struct drm_bridge *bridge,
 		goto err_disable_irq;
 	}
 
+	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(dev, "failed to get follow-up bridge: %d\n", ret);
+		goto err_unregister_dp_aux;
+	}
+
+	ret = drm_bridge_attach(encoder, dp->next_bridge, bridge,
+				DRM_BRIDGE_ATTACH_NO_CONNECTOR);
+	if (ret) {
+		dev_err(dev, "Failed to attach next bridge: %d\n", ret);
+		goto err_put_next_bridge;
+	}
+
 	return 0;
 
+err_put_next_bridge:
+	drm_bridge_put(dp->next_bridge);
+
+err_unregister_dp_aux:
+	drm_dp_aux_unregister(&dp->aux);
+
 err_disable_irq:
 	disable_irq(dp->irq);
 	cancel_work_sync(&dp->hpd_work);
@@ -1905,6 +1927,7 @@ static void dw_dp_bridge_detach(struct drm_bridge *bridge)
 {
 	struct dw_dp *dp = bridge_to_dp(bridge);
 
+	drm_bridge_put(dp->next_bridge);
 	drm_dp_aux_unregister(&dp->aux);
 	disable_irq(dp->irq);
 	cancel_work_sync(&dp->hpd_work);

-- 
2.53.0