[PATCH v3 1/3] drm/display: add transparent bridge helper

[Neil Armstrong]

Hi,

On 02/08/2023 03:18, Dmitry Baryshkov wrote:
> Define a helper for creating simple transparent bridges which serve the
> only purpose of linking devices into the bridge chain up to the last
> bridge representing the connector. This is especially useful for
> DP/USB-C bridge chains, which can span across several devices, but do
> not require any additional functionality from the intermediate bridges.
> 
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
> ---
>   drivers/gpu/drm/display/Kconfig             |   9 ++
>   drivers/gpu/drm/display/Makefile            |   2 +
>   drivers/gpu/drm/display/drm_simple_bridge.c | 127 ++++++++++++++++++++

I wonder why drm/display/ and not drm/bridge ?

It's an helper, but it's mainly a bridge.

>   include/drm/display/drm_simple_bridge.h     |  19 +++
>   4 files changed, 157 insertions(+)
>   create mode 100644 drivers/gpu/drm/display/drm_simple_bridge.c
>   create mode 100644 include/drm/display/drm_simple_bridge.h
> 
> 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..9e80efe67b93
> --- /dev/null
> +++ b/drivers/gpu/drm/display/drm_simple_bridge.c
> @@ -0,0 +1,127 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright (C) 2023 Linaro Ltd.
> + *
> + * Author: Dmitry Baryshkov <dmitry.baryshkov at 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;
> +#ifdef CONFIG_OF
> +	data->bridge.of_node = data->dev->of_node;
> +#endif

I think the whole stuff should depend on OF since devm_drm_of_get_bridge() is a no-op when !OF

> +
> +	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 at 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 at 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

The design looks fine, but I'll need another review.

Thanks,
Neil