Re: [PATCH v8 03/10] drm/bridge: Implement generic USB Type-C DP HPD bridge

[Chaoyi Chen <chaoyi.chen@rock-chips.com>]

On 11/3/2025 9:48 PM, Heikki Krogerus wrote:

>>>> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
>>>> index a250afd8d662..17257b223a28 100644
>>>> --- a/drivers/gpu/drm/bridge/Kconfig
>>>> +++ b/drivers/gpu/drm/bridge/Kconfig
>>>> @@ -23,13 +23,16 @@ config DRM_AUX_BRIDGE
>>>>    	  build bridges chain.
>>>>    config DRM_AUX_HPD_BRIDGE
>>>> -	tristate
>>>> +	tristate "AUX HPD bridge support"
>>> Why? No, this is supposed to be selected by other drivers. Users don't
>>> know an wouldn't know what is this.
>> In v7, I implemented an additional module for selecting this option. But
>> Heikki believes that it would be better to merge the two modules into one.
> Like I said before, I was merely curious why not just squash the
> support into that AUX_PD_HPD_BRIDGE. If that does not make sense, then
> so be it - make it a "Display Interface Bridge" driver like you
> originally proposed.

Yes, it is.


>>>>    	depends on DRM_BRIDGE && OF
>>>>    	select AUXILIARY_BUS
>>>>    	help
>>>>    	  Simple bridge that terminates the bridge chain and provides HPD
>>>>    	  support.
>>>> +	  Specifically, if you want a default Type-C DisplayPort HPD bridge for
>>>> +	  each port of the Type-C controller, say Y here.
>>>> +
>>>>    menu "Display Interface Bridges"
>>>>    	depends on DRM && DRM_BRIDGE
>>>> diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
>>>> index c7dc03182e59..2998937444bc 100644
>>>> --- a/drivers/gpu/drm/bridge/Makefile
>>>> +++ b/drivers/gpu/drm/bridge/Makefile
>>>> @@ -1,6 +1,12 @@
>>>>    # SPDX-License-Identifier: GPL-2.0
>>>>    obj-$(CONFIG_DRM_AUX_BRIDGE) += aux-bridge.o
>>>> -obj-$(CONFIG_DRM_AUX_HPD_BRIDGE) += aux-hpd-bridge.o
>>>> +
>>>> +hpd-bridge-y := aux-hpd-bridge.o
>>>> +ifneq ($(CONFIG_TYPEC),)
>>>> +hpd-bridge-y += aux-hpd-typec-dp-bridge.o
>>>> +endif
>>>> +obj-$(CONFIG_DRM_AUX_HPD_BRIDGE) += hpd-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-hpd-bridge.c b/drivers/gpu/drm/bridge/aux-hpd-bridge.c
>>>> index 2e9c702c7087..11ad6dc776c7 100644
>>>> --- a/drivers/gpu/drm/bridge/aux-hpd-bridge.c
>>>> +++ b/drivers/gpu/drm/bridge/aux-hpd-bridge.c
>>>> @@ -12,6 +12,8 @@
>>>>    #include <drm/drm_bridge.h>
>>>>    #include <drm/bridge/aux-bridge.h>
>>>> +#include "aux-hpd-bridge.h"
>>>> +
>>>>    static DEFINE_IDA(drm_aux_hpd_bridge_ida);
>>>>    struct drm_aux_hpd_bridge_data {
>>>> @@ -204,7 +206,26 @@ static struct auxiliary_driver drm_aux_hpd_bridge_drv = {
>>>>    	.id_table = drm_aux_hpd_bridge_table,
>>>>    	.probe = drm_aux_hpd_bridge_probe,
>>>>    };
>>>> -module_auxiliary_driver(drm_aux_hpd_bridge_drv);
>>>> +
>>>> +static int drm_aux_hpd_bridge_mod_init(void)
>>>> +{
>>>> +	int ret;
>>>> +
>>>> +	ret = auxiliary_driver_register(&drm_aux_hpd_bridge_drv);
>>>> +	if (ret)
>>>> +		return ret;
>>>> +
>>>> +	return drm_aux_hpd_typec_dp_bridge_init();
>>>> +}
>>>> +
>>>> +static void drm_aux_hpd_bridge_mod_exit(void)
>>>> +{
>>>> +	drm_aux_hpd_typec_dp_bridge_exit();
>>>> +	auxiliary_driver_unregister(&drm_aux_hpd_bridge_drv);
>>>> +}
>>>> +
>>>> +module_init(drm_aux_hpd_bridge_mod_init);
>>>> +module_exit(drm_aux_hpd_bridge_mod_exit);
>>>>    MODULE_AUTHOR("Dmitry Baryshkov <dmitry.baryshkov@linaro.org>");
>>>>    MODULE_DESCRIPTION("DRM HPD bridge");
>>>> diff --git a/drivers/gpu/drm/bridge/aux-hpd-bridge.h b/drivers/gpu/drm/bridge/aux-hpd-bridge.h
>>>> new file mode 100644
>>>> index 000000000000..69364731c2f1
>>>> --- /dev/null
>>>> +++ b/drivers/gpu/drm/bridge/aux-hpd-bridge.h
>>>> @@ -0,0 +1,13 @@
>>>> +/* SPDX-License-Identifier: GPL-2.0-only */
>>>> +#ifndef AUX_HPD_BRIDGE_H
>>>> +#define AUX_HPD_BRIDGE_H
>>>> +
>>>> +#if IS_REACHABLE(CONFIG_TYPEC)
>>>> +int drm_aux_hpd_typec_dp_bridge_init(void);
>>>> +void drm_aux_hpd_typec_dp_bridge_exit(void);
>>>> +#else
>>>> +static inline int drm_aux_hpd_typec_dp_bridge_init(void) { return 0; }
>>>> +static inline void drm_aux_hpd_typec_dp_bridge_exit(void) { }
>>>> +#endif /* IS_REACHABLE(CONFIG_TYPEC) */
>>>> +
>>>> +#endif /* AUX_HPD_BRIDGE_H */
>>>> diff --git a/drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c b/drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c
>>>> new file mode 100644
>>>> index 000000000000..6f2a1fca0fc5
>>>> --- /dev/null
>>>> +++ b/drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c
>>>> @@ -0,0 +1,47 @@
>>>> +// SPDX-License-Identifier: GPL-2.0+
>>>> +#include <linux/of.h>
>>>> +#include <linux/usb/typec_altmode.h>
>>>> +#include <linux/usb/typec_dp.h>
>>>> +#include <linux/usb/typec_notify.h>
>>>> +
>>>> +#include <drm/bridge/aux-bridge.h>
>>>> +
>>>> +#include "aux-hpd-bridge.h"
>>>> +
>>>> +#if IS_REACHABLE(CONFIG_TYPEC)
>>>> +static int drm_typec_bus_event(struct notifier_block *nb,
>>>> +			       unsigned long action, void *data)
>>>> +{
>>> This feels like this should be a part of the Type-C subsystem rather
>>> than DRM.
>> In v7, this used to be a part of the Type-C subsystem. I'm not sure what
>> Heikki thinks about this.
> Your original proposal of making the entire TYPEC subsystem depend on
> DRM is _not_ going to happen. In general, if I've now understood this
> correctly, this thing probable should be a "display interface bridge
> driver", similar to what you proposed in the previous version.
>
> Note also that you could make it selected automatically, so there is
> no need for user selectable option if that's the preference. Kconfig
> and Makefile gives you options on how to do that. For example, maybe
> this Kconfig works (or does not, but something like it will):
>
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index a250afd8d662..7487024ba2ce 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -30,6 +30,15 @@ config DRM_AUX_HPD_BRIDGE
>            Simple bridge that terminates the bridge chain and provides HPD
>            support.
>   
> +if DRM_AUX_HPD_BRIDGE
> +
> +config DRM_AUX_HPD_TYPEC_BRIDGE
> +       tristate
> +       depends on TYPEC || !TYPEC
> +       default TYPEC
> +
> +endif /* DRM_AUX_HPD_BRIDGE */
> +
>   menu "Display Interface Bridges"
>          depends on DRM && DRM_BRIDGE

Thank you for your code. I think both of your points make sense. So choosing the approach you mentioned now (similar to v7) might be a reasonable compromise.



>   
>
>
> thanks,
>
-- 
Best,
Chaoyi


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