Re: [PATCH v4 1/3] drm/bridge: add transparent bridge helper

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Oct 11, 2023 at 02:10:16AM +0300, 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@linaro.org>
> ---
>  drivers/gpu/drm/bridge/Kconfig      |   9 ++
>  drivers/gpu/drm/bridge/Makefile     |   1 +
>  drivers/gpu/drm/bridge/aux-bridge.c | 132 ++++++++++++++++++++++++++++
>  include/drm/bridge/aux-bridge.h     |  19 ++++
>  4 files changed, 161 insertions(+)
>  create mode 100644 drivers/gpu/drm/bridge/aux-bridge.c
>  create mode 100644 include/drm/bridge/aux-bridge.h
> 
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index ba82a1142adf..f12eab62799f 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -12,6 +12,15 @@ config DRM_PANEL_BRIDGE
>  	help
>  	  DRM bridge wrapper of DRM panels
>  
> +config DRM_AUX_BRIDGE
> +	tristate
> +	depends on DRM_BRIDGE && OF
> +	select AUXILIARY_BUS
> +	select DRM_PANEL_BRIDGE
> +	help
> +	  Simple transparent bridge that is used by several non-DRM drivers to
> +	  build bridges chain.
> +
>  menu "Display Interface Bridges"
>  	depends on DRM && DRM_BRIDGE
>  
> diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
> index 2b892b7ed59e..918e3bfff079 100644
> --- a/drivers/gpu/drm/bridge/Makefile
> +++ b/drivers/gpu/drm/bridge/Makefile
> @@ -1,4 +1,5 @@
>  # SPDX-License-Identifier: GPL-2.0
> +obj-$(CONFIG_DRM_AUX_BRIDGE) += aux-bridge.o
>  obj-$(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
> diff --git a/drivers/gpu/drm/bridge/aux-bridge.c b/drivers/gpu/drm/bridge/aux-bridge.c
> new file mode 100644
> index 000000000000..13fe794592f2
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/aux-bridge.c
> @@ -0,0 +1,132 @@
> +// 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/bridge/aux-bridge.h>
> +
> +static DEFINE_IDA(aux_bridge_ida);
> +
> +static void drm_aux_bridge_release(struct device *dev)
> +{
> +	struct auxiliary_device *adev = to_auxiliary_dev(dev);
> +
> +	ida_free(&aux_bridge_ida, adev->id);
> +
> +	kfree(adev);
> +}
> +
> +static void drm_aux_bridge_unregister_adev(void *_adev)
> +{
> +	struct auxiliary_device *adev = _adev;
> +
> +	auxiliary_device_delete(adev);
> +	auxiliary_device_uninit(adev);
> +}
> +
> +int drm_aux_bridge_register(struct device *parent)
> +{
> +	struct auxiliary_device *adev;
> +	int ret;
> +
> +	adev = kzalloc(sizeof(*adev), GFP_KERNEL);
> +	if (!adev)
> +		return -ENOMEM;
> +
> +	ret = ida_alloc(&aux_bridge_ida, GFP_KERNEL);
> +	if (ret < 0) {
> +		kfree(adev);
> +		return ret;
> +	}
> +
> +	adev->id = ret;
> +	adev->name = "aux_bridge";
> +	adev->dev.parent = parent;
> +#ifdef CONFIG_OF
> +	adev->dev.of_node = parent->of_node;
> +#endif
> +	adev->dev.release = drm_aux_bridge_release;
> +
> +	ret = auxiliary_device_init(adev);
> +	if (ret) {
> +		ida_free(&aux_bridge_ida, adev->id);
> +		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_aux_bridge_unregister_adev, adev);
> +}
> +EXPORT_SYMBOL_GPL(drm_aux_bridge_register);

kerneldoc for new interfaces please (you can wait if you're not sure
whether this design will land or not, but for merging we really want all
drm interfaces exposed to drivers documented). Ideally with enough links
to other interfaces/structs/docs so that people can understand what this
does and why.

Thanks, Sima
> +
> +struct drm_aux_bridge_data {
> +	struct drm_bridge bridge;
> +	struct drm_bridge *next_bridge;
> +	struct device *dev;
> +};
> +
> +static int drm_aux_bridge_attach(struct drm_bridge *bridge,
> +				    enum drm_bridge_attach_flags flags)
> +{
> +	struct drm_aux_bridge_data *data;
> +
> +	if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR))
> +		return -EINVAL;
> +
> +	data = container_of(bridge, struct drm_aux_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_aux_bridge_funcs = {
> +	.attach	= drm_aux_bridge_attach,
> +};
> +
> +static int drm_aux_bridge_probe(struct auxiliary_device *auxdev,
> +				   const struct auxiliary_device_id *id)
> +{
> +	struct drm_aux_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_aux_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_aux_bridge_table[] = {
> +	{ .name = KBUILD_MODNAME ".aux_bridge" },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(auxiliary, drm_aux_bridge_table);
> +
> +static struct auxiliary_driver drm_aux_bridge_drv = {
> +	.name = "aux_bridge",
> +	.id_table = drm_aux_bridge_table,
> +	.probe = drm_aux_bridge_probe,
> +};
> +module_auxiliary_driver(drm_aux_bridge_drv);
> +
> +MODULE_AUTHOR("Dmitry Baryshkov <dmitry.baryshkov@linaro.org>");
> +MODULE_DESCRIPTION("DRM transparent bridge");
> +MODULE_LICENSE("GPL");
> diff --git a/include/drm/bridge/aux-bridge.h b/include/drm/bridge/aux-bridge.h
> new file mode 100644
> index 000000000000..441ab3f0e920
> --- /dev/null
> +++ b/include/drm/bridge/aux-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_AUX_BRIDGE_H
> +#define DRM_AUX_BRIDGE_H
> +
> +#if IS_ENABLED(CONFIG_DRM_AUX_BRIDGE)
> +int drm_aux_bridge_register(struct device *parent);
> +#else
> +static inline int drm_aux_bridge_register(struct device *parent)
> +{
> +	return 0;
> +}
> +#endif
> +
> +#endif
> -- 
> 2.39.2
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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