Re: [PATCH v9 03/10] drm/bridge: Implement generic USB Type-C DP HPD bridge

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

On 11/17/2025 4:40 PM, Heikki Krogerus wrote:

> Tue, Nov 11, 2025 at 06:50:33PM +0800, Chaoyi Chen kirjoitti:
>> From: Chaoyi Chen <chaoyi.chen@rock-chips.com>
>>
>> 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 <chaoyi.chen@rock-chips.com>
> Normally there is no "help" section for hidden config options. I
> guess it can not cause any harm? It is a bit confusing, though. But
> FWIW:

The hidden options "DRM_AUX_BRIDGE" and "DRM_AUX_HPD_BRIDGE" also have a help section.

I think this is just for comment purposes :)


>
> Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
>
>> ---
>>
>> 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  | 50 +++++++++++++++++++
>>   3 files changed, 61 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..9cb6a0cb0f0a
>> --- /dev/null
>> +++ b/drivers/gpu/drm/bridge/aux-hpd-typec-dp-bridge.c
>> @@ -0,0 +1,50 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +#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 typec_altmode *alt = (struct typec_altmode *)data;
>> +
>> +	if (action != TYPEC_ALTMODE_REGISTERED)
>> +		goto done;
>> +
>> +	if (is_typec_partner(&alt->dev) || alt->svid != USB_TYPEC_DP_SID)
>> +		goto done;
>> +
>> +	/*
>> +	 * alt->dev.parent->parent : USB-C controller device
>> +	 * alt->dev.parent         : USB-C connector device
>> +	 */
>> +	drm_dp_hpd_bridge_register(alt->dev.parent->parent,
>> +				   to_of_node(alt->dev.parent->fwnode));
>> +
>> +done:
>> +	return NOTIFY_OK;
>> +}
>> +
>> +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)
>> +{
>> +	typec_altmode_unregister_notify(&drm_typec_event_nb);
>> +}
>> +
>> +static int __init drm_aux_hpd_typec_dp_bridge_module_init(void)
>> +{
>> +	typec_altmode_register_notify(&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");
>> -- 
>> 2.51.1

-- 
Best,
Chaoyi