drm/bridge: implement generic DP HPD bridge

Several USB-C controllers implement a pretty simple DRM bridge which
implements just the HPD notification operations. Add special helper
for creating such simple bridges.

Acked-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231203114333.1305826-5-dmitry.baryshkov@linaro.org

drivers/gpu/drm/bridge/Kconfig

@@ -21,6 +21,14 @@ config DRM_AUX_BRIDGE
 	  Simple transparent bridge that is used by several non-DRM drivers to
 	  build bridges chain.
 
+config DRM_AUX_HPD_BRIDGE
+	tristate
+	depends on DRM_BRIDGE && OF
+	select AUXILIARY_BUS
+	help
+	  Simple bridge that terminates the bridge chain and provides HPD
+	  support.
+
 menu "Display Interface Bridges"
 	depends on DRM && DRM_BRIDGE
 

drivers/gpu/drm/bridge/Makefile

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_DRM_AUX_BRIDGE) += aux-bridge.o
+obj-$(CONFIG_DRM_AUX_HPD_BRIDGE) += aux-hpd-bridge.o
 obj-$(CONFIG_DRM_CHIPONE_ICN6211) += chipone-icn6211.o
 obj-$(CONFIG_DRM_CHRONTEL_CH7033) += chrontel-ch7033.o
 obj-$(CONFIG_DRM_CROS_EC_ANX7688) += cros-ec-anx7688.o

drivers/gpu/drm/bridge/aux-hpd-bridge.c

@@ -0,0 +1,163 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2023 Linaro Ltd.
+ *
+ * Author: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
+ */
+#include <linux/auxiliary_bus.h>
+#include <linux/module.h>
+#include <linux/of_device.h>
+
+#include <drm/drm_bridge.h>
+#include <drm/bridge/aux-bridge.h>
+
+static DEFINE_IDA(drm_aux_hpd_bridge_ida);
+
+struct drm_aux_hpd_bridge_data {
+	struct drm_bridge bridge;
+	struct device *dev;
+};
+
+static void drm_aux_hpd_bridge_release(struct device *dev)
+{
+	struct auxiliary_device *adev = to_auxiliary_dev(dev);
+
+	ida_free(&drm_aux_hpd_bridge_ida, adev->id);
+
+	of_node_put(adev->dev.platform_data);
+
+	kfree(adev);
+}
+
+static void drm_aux_hpd_bridge_unregister_adev(void *_adev)
+{
+	struct auxiliary_device *adev = _adev;
+
+	auxiliary_device_delete(adev);
+	auxiliary_device_uninit(adev);
+}
+
+/**
+ * drm_dp_hpd_bridge_register - Create a simple HPD DisplayPort bridge
+ * @parent: device instance providing this bridge
+ * @np: device node pointer corresponding to this bridge instance
+ *
+ * Creates a simple DRM bridge with the type set to
+ * DRM_MODE_CONNECTOR_DisplayPort, which terminates the bridge chain and is
+ * able to send the HPD events.
+ *
+ * Return: device instance that will handle created bridge or an error code
+ * encoded into the pointer.
+ */
+struct device *drm_dp_hpd_bridge_register(struct device *parent,
+					  struct device_node *np)
+{
+	struct auxiliary_device *adev;
+	int ret;
+
+	adev = kzalloc(sizeof(*adev), GFP_KERNEL);
+	if (!adev)
+		return ERR_PTR(-ENOMEM);
+
+	ret = ida_alloc(&drm_aux_hpd_bridge_ida, GFP_KERNEL);
+	if (ret < 0) {
+		kfree(adev);
+		return ERR_PTR(ret);
+	}
+
+	adev->id = ret;
+	adev->name = "dp_hpd_bridge";
+	adev->dev.parent = parent;
+	adev->dev.of_node = parent->of_node;
+	adev->dev.release = drm_aux_hpd_bridge_release;
+	adev->dev.platform_data = np;
+
+	ret = auxiliary_device_init(adev);
+	if (ret) {
+		ida_free(&drm_aux_hpd_bridge_ida, adev->id);
+		kfree(adev);
+		return ERR_PTR(ret);
+	}
+
+	ret = auxiliary_device_add(adev);
+	if (ret) {
+		auxiliary_device_uninit(adev);
+		return ERR_PTR(ret);
+	}
+
+	ret = devm_add_action_or_reset(parent, drm_aux_hpd_bridge_unregister_adev, adev);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return &adev->dev;
+}
+EXPORT_SYMBOL_GPL(drm_dp_hpd_bridge_register);
+
+/**
+ * drm_aux_hpd_bridge_notify - notify hot plug detection events
+ * @dev: device created for the HPD bridge
+ * @status: output connection status
+ *
+ * A wrapper around drm_bridge_hpd_notify() that is used to report hot plug
+ * detection events for bridges created via drm_dp_hpd_bridge_register().
+ *
+ * This function shall be called in a context that can sleep.
+ */
+void drm_aux_hpd_bridge_notify(struct device *dev, enum drm_connector_status status)
+{
+	struct auxiliary_device *adev = to_auxiliary_dev(dev);
+	struct drm_aux_hpd_bridge_data *data = auxiliary_get_drvdata(adev);
+
+	if (!data)
+		return;
+
+	drm_bridge_hpd_notify(&data->bridge, status);
+}
+EXPORT_SYMBOL_GPL(drm_aux_hpd_bridge_notify);
+
+static int drm_aux_hpd_bridge_attach(struct drm_bridge *bridge,
+				     enum drm_bridge_attach_flags flags)
+{
+	return flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR ? 0 : -EINVAL;
+}
+
+static const struct drm_bridge_funcs drm_aux_hpd_bridge_funcs = {
+	.attach	= drm_aux_hpd_bridge_attach,
+};
+
+static int drm_aux_hpd_bridge_probe(struct auxiliary_device *auxdev,
+				    const struct auxiliary_device_id *id)
+{
+	struct drm_aux_hpd_bridge_data *data;
+
+	data = devm_kzalloc(&auxdev->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->dev = &auxdev->dev;
+	data->bridge.funcs = &drm_aux_hpd_bridge_funcs;
+	data->bridge.of_node = dev_get_platdata(data->dev);
+	data->bridge.ops = DRM_BRIDGE_OP_HPD;
+	data->bridge.type = id->driver_data;
+
+	auxiliary_set_drvdata(auxdev, data);
+
+	return devm_drm_bridge_add(data->dev, &data->bridge);
+}
+
+static const struct auxiliary_device_id drm_aux_hpd_bridge_table[] = {
+	{ .name = KBUILD_MODNAME ".dp_hpd_bridge", .driver_data = DRM_MODE_CONNECTOR_DisplayPort, },
+	{},
+};
+MODULE_DEVICE_TABLE(auxiliary, drm_aux_hpd_bridge_table);
+
+static struct auxiliary_driver drm_aux_hpd_bridge_drv = {
+	.name = "aux_hpd_bridge",
+	.id_table = drm_aux_hpd_bridge_table,
+	.probe = drm_aux_hpd_bridge_probe,
+};
+module_auxiliary_driver(drm_aux_hpd_bridge_drv);
+
+MODULE_AUTHOR("Dmitry Baryshkov <dmitry.baryshkov@linaro.org>");
+MODULE_DESCRIPTION("DRM HPD bridge");
+MODULE_LICENSE("GPL");

include/drm/bridge/aux-bridge.h

@@ -7,6 +7,8 @@
 #ifndef DRM_AUX_BRIDGE_H
 #define DRM_AUX_BRIDGE_H
 
+#include <drm/drm_connector.h>
+
 #if IS_ENABLED(CONFIG_DRM_AUX_BRIDGE)
 int drm_aux_bridge_register(struct device *parent);
 #else
@@ -16,4 +18,20 @@ static inline int drm_aux_bridge_register(struct device *parent)
 }
 #endif
 
+#if IS_ENABLED(CONFIG_DRM_AUX_HPD_BRIDGE)
+struct device *drm_dp_hpd_bridge_register(struct device *parent,
+					  struct device_node *np);
+void drm_aux_hpd_bridge_notify(struct device *dev, enum drm_connector_status status);
+#else
+static inline struct device *drm_dp_hpd_bridge_register(struct device *parent,
+							struct device_node *np)
+{
+	return 0;
+}
+
+static inline void drm_aux_hpd_bridge_notify(struct device *dev, enum drm_connector_status status)
+{
+}
+#endif
+
 #endif