Subject: Re: [PATCH v15 1/9] drm/bridge: Implement generic USB Type-C DP HPD bridge

From: Chaoyi Chen <[email-masked]>
Date: Fri, 29 May 2026 09:18:03 +0800

Hello Nicolas,

On 5/28/2026 11:37 PM, Nicolas Frattaroli wrote:
> On Wednesday, 4 March 2026 10:41:44 Central European Summer Time Chaoyi Chen wrote:
>> From: Chaoyi Chen <[email-masked]>
>>
>> The HPD function of Type-C DP is implemented through
>> drm_connector_oob_hotplug_event(). For embedded DP, it is required
>> that the DRM connector fwnode corresponds to the Type-C port fwnode.
>>
>> To describe the relationship between the DP controller and the Type-C
>> port device, we usually using drm_bridge to build a bridge chain.
>>
>> Now several USB-C controller drivers have already implemented the DP
>> HPD bridge function provided by aux-hpd-bridge.c, it will build a DP
>> HPD bridge on USB-C connector port device.
>>
>> But this requires the USB-C controller driver to manually register the
>> HPD bridge. If the driver does not implement this feature, the bridge
>> will not be create.
>>
>> So this patch implements a generic DP HPD bridge based on
>> aux-hpd-bridge.c. It will monitor Type-C bus events, and when a
>> Type-C port device containing the DP svid is registered, it will
>> create an HPD bridge for it without the need for the USB-C controller
>> driver to implement it.
>>
>> Signed-off-by: Chaoyi Chen <[email-masked]>
>> Reviewed-by: Heikki Krogerus <[email-masked]>
>> ---
>>
>> (no changes since v14)
>>
>> Changes in v13:
>> - Only register drm dp hpd bridge for typec port altmode device.
>>
>> (no changes since v12)
>>
>> Changes in v11:
>> - Switch to using typec bus notifiers.
>>
>> (no changes since v10)
>>
>> Changes in v9:
>> - Remove the exposed DRM_AUX_HPD_BRIDGE option, and select
>> DRM_AUX_HPD_TYPEC_BRIDGE when it is available.
>> - Add more commit comment about problem background.
>>
>> Changes in v8:
>> - Merge generic DP HPD bridge into one module.
>> ---
>>
>>  drivers/gpu/drm/bridge/Kconfig                | 10 ++++
>>  drivers/gpu/drm/bridge/Makefile               |  1 +
>>  .../gpu/drm/bridge/aux-hpd-typec-dp-bridge.c  | 49 +++++++++++++++++++
>>  3 files changed, 60 insertions(+)
>>  create mode 100644 drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c
>>
>> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
>> index a250afd8d662..559487aa09a9 100644
>> --- a/drivers/gpu/drm/bridge/Kconfig
>> +++ b/drivers/gpu/drm/bridge/Kconfig
>> @@ -30,6 +30,16 @@ 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
>> +	help
>> +	  Simple bridge that terminates the bridge chain and provides HPD
>> +	  support. It build bridge on each USB-C connector device node.
>> +endif
>> +
>>  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..a3a0393d2e72 100644
>> --- a/drivers/gpu/drm/bridge/Makefile
>> +++ b/drivers/gpu/drm/bridge/Makefile
>> @@ -1,6 +1,7 @@
>>  # SPDX-License-Identifier: GPL-2.0
>>  obj-$(CONFIG_DRM_AUX_BRIDGE) += aux-bridge.o
>>  obj-$(CONFIG_DRM_AUX_HPD_BRIDGE) += aux-hpd-bridge.o
>> +obj-$(CONFIG_DRM_AUX_HPD_TYPEC_BRIDGE) += aux-hpd-typec-dp-bridge.o
>>  obj-$(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-typec-dp-bridge.c b/drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c
>> new file mode 100644
>> index 000000000000..d915e0fb0668
>> --- /dev/null
>> +++ b/drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c
>> @@ -0,0 +1,49 @@
>> +// SPDX-License-Identifier: GPL-2.0+
> 
> Having a copyright statement added here is likely required.
> Something like
> 
> /*
>  * Copyright (C) 2026 Rockchip Electronics Co., Ltd.
>  *
>  * Author: Chaoyi Chen <[email-masked]>
>  */
> 
> will suffice. While I hope it's never relevant for a driver this
> small, explicit copyright statements in this form have a legal
> effect in some jurisdictions like the US, where by law it
> automatically dismisses the defense that the copyright holder
> wasn't known.
> 

Oh! I hadn't noticed that. Thank you for your legal advice.

>> +#include <linux/of.h>
>> +#include <linux/usb/typec_altmode.h>
>> +#include <linux/usb/typec_dp.h>
>> +
>> +#include <drm/bridge/aux-bridge.h>
>> +
>> +static int drm_typec_bus_event(struct notifier_block *nb,
>> +			       unsigned long action, void *data)
>> +{
>> +	struct device *dev = (struct device *)data;
> 
> Small nitpick: The explicit (struct device *) cast of data isn't
> needed here. Just
> 
>     struct device *dev = data;
> 
> will work fine. The benefit is that if the type of "data" ever changes
> (e.g. from void *data to const void *data) then we're not silencing
> a warning/error through an explicit cast.
>

Yep. Will fix in v2.

>> +	struct typec_altmode *alt = to_typec_altmode(dev);
>> +
>> +	if (action != BUS_NOTIFY_ADD_DEVICE)
>> +		goto done;
>> +
>> +	/*
>> +	 * alt->dev.parent->parent : USB-C controller device
>> +	 * alt->dev.parent         : USB-C connector device
>> +	 */
>> +	if (is_typec_port_altmode(&alt->dev) && alt->svid == USB_TYPEC_DP_SID)
>> +		drm_dp_hpd_bridge_register(alt->dev.parent->parent,
>> +					   to_of_node(alt->dev.parent->fwnode));
>> +
>> +done:
>> +	return NOTIFY_OK;
>> +}
> 
> Nitpicking: the "done" label and "goto done" here is redundant.
> You could remove the label and replace the goto with another
> "return NOTIFY_OK;". There's no functional change here though.
> 

Will fix in v2.

>> +
>> +static struct notifier_block drm_typec_event_nb = {
>> +	.notifier_call = drm_typec_bus_event,
>> +};
>> +
>> +static void drm_aux_hpd_typec_dp_bridge_module_exit(void)
>> +{
>> +	bus_unregister_notifier(&typec_bus, &drm_typec_event_nb);
>> +}
>> +
>> +static int __init drm_aux_hpd_typec_dp_bridge_module_init(void)
>> +{
>> +	bus_register_notifier(&typec_bus, &drm_typec_event_nb);
>> +
>> +	return 0;
>> +}
>> +
>> +module_init(drm_aux_hpd_typec_dp_bridge_module_init);
>> +module_exit(drm_aux_hpd_typec_dp_bridge_module_exit);
>> +
>> +MODULE_DESCRIPTION("DRM TYPEC DP HPD BRIDGE");
>> +MODULE_LICENSE("GPL");
>>
> 
> Feel free to add yourself as MODULE_AUTHOR here. :)
> 
> With those things changed:
> 
> Reviewed-by: Nicolas Frattaroli <[email-masked]>
> 
> Kind regards,
> Nicolas Frattaroli
> 
> 
> 

-- 
Best, 
Chaoyi