[PATCH v12 10/23] 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

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.

Reviewed-by: Chaoyi Chen <chaoyi.chen@rock-chips.com>
Tested-by: Igor Paunovic <royalnet026@gmail.com> # Orange Pi 5+
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
---
 drivers/gpu/drm/bridge/synopsys/dw-dp.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-dp.c b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
index 5db9063ee97e..74ba1306caee 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-dp.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-dp.c
@@ -327,6 +327,7 @@ struct dw_dp {
 
 	struct dw_dp_link link;
 	struct dw_dp_plat_data plat_data;
+	struct drm_bridge *next_bridge;
 	u8 pixel_mode;
 
 	DECLARE_BITMAP(sdp_reg_bank, SDP_REG_BANK_SIZE);
@@ -1895,7 +1896,22 @@ static int dw_dp_bridge_attach(struct drm_bridge *bridge,
 
 	enable_irq(dp->irq);
 
+	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_disable_irq;
+	}
+
 	return 0;
+
+err_disable_irq:
+	disable_irq(dp->irq);
+	cancel_work_sync(&dp->hpd_work);
+
+	drm_dp_aux_unregister(&dp->aux);
+
+	return ret;
 }
 
 static void dw_dp_bridge_detach(struct drm_bridge *bridge)
@@ -2061,6 +2077,13 @@ void dw_dp_unbind(struct dw_dp *dp)
 }
 EXPORT_SYMBOL_GPL(dw_dp_unbind);
 
+static void dw_dp_put_next_bridge(void *data)
+{
+	struct dw_dp *dp = data;
+
+	drm_bridge_put(dp->next_bridge);
+}
+
 static void dw_dp_phy_exit(void *data)
 {
 	struct dw_dp *dp = data;
@@ -2156,6 +2179,16 @@ struct dw_dp *dw_dp_probe(struct platform_device *pdev, const struct dw_dp_plat_
 	if (ret)
 		return ERR_PTR(ret);
 
+	dp->next_bridge = of_drm_get_bridge_by_endpoint(dev->of_node, 1, 0);
+	if (IS_ERR(dp->next_bridge)) {
+		dev_err_probe(dev, PTR_ERR(dp->next_bridge), "failed to get follow-up bridge\n");
+		return ERR_CAST(dp->next_bridge);
+	}
+
+	ret = devm_add_action_or_reset(dev, dw_dp_put_next_bridge, dp);
+	if (ret)
+		return ERR_PTR(ret);
+
 	dw_dp_init_hw(dp);
 
 	ret = phy_init(dp->phy);

-- 
2.53.0