[v2,1/3] drm/display: add transparent bridge helper

diff --git a/drivers/gpu/drm/display/Kconfig b/drivers/gpu/drm/display/Kconfig
index 09712b88a5b8..a6132984b9e3 100644
--- a/drivers/gpu/drm/display/Kconfig
+++ b/drivers/gpu/drm/display/Kconfig
@@ -49,3 +49,12 @@  config DRM_DP_CEC
 
 	  Note: not all adapters support this feature, and even for those
 	  that do support this they often do not hook up the CEC pin.
+
+config DRM_SIMPLE_BRIDGE
+	tristate
+	depends on DRM
+	select AUXILIARY_BUS
+	select DRM_PANEL_BRIDGE
+	help
+	  Simple transparent bridge that is used by several drivers to build
+	  bridges chain.
diff --git a/drivers/gpu/drm/display/Makefile b/drivers/gpu/drm/display/Makefile
index 17ac4a1006a8..6e2b0d7f24b3 100644
--- a/drivers/gpu/drm/display/Makefile
+++ b/drivers/gpu/drm/display/Makefile
@@ -16,3 +16,5 @@  drm_display_helper-$(CONFIG_DRM_DP_AUX_CHARDEV) += drm_dp_aux_dev.o
 drm_display_helper-$(CONFIG_DRM_DP_CEC) += drm_dp_cec.o
 
 obj-$(CONFIG_DRM_DISPLAY_HELPER) += drm_display_helper.o
+
+obj-$(CONFIG_DRM_SIMPLE_BRIDGE) += drm_simple_bridge.o
diff --git a/drivers/gpu/drm/display/drm_simple_bridge.c b/drivers/gpu/drm/display/drm_simple_bridge.c
new file mode 100644
index 000000000000..94cdd927b708
--- /dev/null
+++ b/drivers/gpu/drm/display/drm_simple_bridge.c
@@ -0,0 +1,125 @@ 
+// 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 <drm/drm_bridge.h>
+#include <drm/display/drm_simple_bridge.h>
+
+static DEFINE_IDA(simple_bridge_ida);
+
+static void drm_simple_bridge_release(struct device *dev)
+{
+	struct auxiliary_device *adev = to_auxiliary_dev(dev);
+
+	kfree(adev);
+}
+
+static void drm_simple_bridge_unregister_adev(void *_adev)
+{
+	struct auxiliary_device *adev = _adev;
+
+	auxiliary_device_delete(adev);
+	auxiliary_device_uninit(adev);
+}
+
+int drm_simple_bridge_register(struct device *parent)
+{
+	struct auxiliary_device *adev;
+	int ret;
+
+	adev = kzalloc(sizeof(*adev), GFP_KERNEL);
+	if (!adev)
+		return -ENOMEM;
+
+	ret = ida_alloc(&simple_bridge_ida, GFP_KERNEL);
+	if (ret < 0)
+		return ret;
+
+	adev->id = ret;
+	adev->name = "simple_bridge";
+	adev->dev.parent = parent;
+	adev->dev.of_node = parent->of_node;
+	adev->dev.release = drm_simple_bridge_release;
+
+	ret = auxiliary_device_init(adev);
+	if (ret) {
+		kfree(adev);
+		return ret;
+	}
+
+	ret = auxiliary_device_add(adev);
+	if (ret) {
+		auxiliary_device_uninit(adev);
+		return ret;
+	}
+
+	return devm_add_action_or_reset(parent, drm_simple_bridge_unregister_adev, adev);
+}
+EXPORT_SYMBOL_GPL(drm_simple_bridge_register);
+
+struct drm_simple_bridge_data {
+	struct drm_bridge bridge;
+	struct drm_bridge *next_bridge;
+	struct device *dev;
+};
+
+static int drm_simple_bridge_attach(struct drm_bridge *bridge,
+				    enum drm_bridge_attach_flags flags)
+{
+	struct drm_simple_bridge_data *data;
+
+	if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR))
+		return -EINVAL;
+
+	data = container_of(bridge, struct drm_simple_bridge_data, bridge);
+
+	return drm_bridge_attach(bridge->encoder, data->next_bridge, bridge,
+				 DRM_BRIDGE_ATTACH_NO_CONNECTOR);
+}
+
+static const struct drm_bridge_funcs drm_simple_bridge_funcs = {
+	.attach	= drm_simple_bridge_attach,
+};
+
+static int drm_simple_bridge_probe(struct auxiliary_device *auxdev,
+				   const struct auxiliary_device_id *id)
+{
+	struct drm_simple_bridge_data *data;
+
+	data = devm_kzalloc(&auxdev->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->dev = &auxdev->dev;
+	data->next_bridge = devm_drm_of_get_bridge(&auxdev->dev, auxdev->dev.of_node, 0, 0);
+	if (IS_ERR(data->next_bridge))
+		return dev_err_probe(&auxdev->dev, PTR_ERR(data->next_bridge),
+				     "failed to acquire drm_bridge\n");
+
+	data->bridge.funcs = &drm_simple_bridge_funcs;
+	data->bridge.of_node = data->dev->of_node;
+
+	return devm_drm_bridge_add(data->dev, &data->bridge);
+}
+
+static const struct auxiliary_device_id drm_simple_bridge_table[] = {
+	{ .name = KBUILD_MODNAME ".simple_bridge" },
+	{},
+};
+MODULE_DEVICE_TABLE(auxiliary, drm_simple_bridge_table);
+
+struct auxiliary_driver drm_simple_bridge_drv = {
+	.name = "simple_bridge",
+	.id_table = drm_simple_bridge_table,
+	.probe = drm_simple_bridge_probe,
+};
+module_auxiliary_driver(drm_simple_bridge_drv);
+
+MODULE_AUTHOR("Dmitry Baryshkov <dmitry.baryshkov@linaro.org>");
+MODULE_DESCRIPTION("DRM simple bridge helper");
+MODULE_LICENSE("GPL");
diff --git a/include/drm/display/drm_simple_bridge.h b/include/drm/display/drm_simple_bridge.h
new file mode 100644
index 000000000000..3da8e1fb1137
--- /dev/null
+++ b/include/drm/display/drm_simple_bridge.h
@@ -0,0 +1,19 @@ 
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2023 Linaro Ltd.
+ *
+ * Author: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
+ */
+#ifndef DRM_SIMPLE_BRIDGE_H
+#define DRM_SIMPLE_BRIDGE_H
+
+#if IS_ENABLED(CONFIG_DRM_SIMPLE_BRIDGE)
+int drm_simple_bridge_register(struct device *parent);
+#else
+static inline int drm_simple_bridge_register(struct device *parent)
+{
+	return 0;
+}
+#endif
+
+#endif