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

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/display/Kconfig             |   9 ++
 drivers/gpu/drm/display/Makefile            |   2 +
 drivers/gpu/drm/display/drm_simple_bridge.c | 120 ++++++++++++++++++++
 include/drm/display/drm_simple_bridge.h     |  19 ++++
 4 files changed, 150 insertions(+)
 create mode 100644 drivers/gpu/drm/display/drm_simple_bridge.c
 create mode 100644 include/drm/display/drm_simple_bridge.h

On Sat, 29 Jul 2023 at 23:43, Dmitry Baryshkov
<dmitry.baryshkov@linaro.org> 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/display/Kconfig             |   9 ++
>  drivers/gpu/drm/display/Makefile            |   2 +
>  drivers/gpu/drm/display/drm_simple_bridge.c | 120 ++++++++++++++++++++
>  include/drm/display/drm_simple_bridge.h     |  19 ++++
>  4 files changed, 150 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..c9966691efb1
> --- /dev/null
> +++ b/drivers/gpu/drm/display/drm_simple_bridge.c
> @@ -0,0 +1,120 @@
> +// 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);
> +}

Forgot EXPORT_SYMBOL_GPL, MODULE_LICENSE, etc. I'll fix that for v2 if
the overall idea is found to be acceptable.

> +
> +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);
> 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
> --
> 2.39.2
>