On Wed, 2 Aug 2023 at 11:15, Neil Armstrong <neil.armstrong@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx>
> > ---
> > 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.
Why not? I'm open to any suggestions.
>
> > 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@xxxxxxxxxx>
> > + */
> > +#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
Hmm, true. Probably we should rework bridges to use fwnode at some point.
>
> > +
> > + 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@xxxxxxxxxx>");
> > +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@xxxxxxxxxx>
> > + */
> > +#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
>
--
With best wishes
Dmitry
