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

[Chaoyi Chen]

Hello Xu Yang,

On 6/26/2026 7:15 PM, Xu Yang wrote:
> On Wed, Mar 04, 2026 at 05:41:44PM +0800, Chaoyi Chen wrote:
>> From: Chaoyi Chen <chaoyi.chen@xxxxxxxxxxxxxx>
>>
>> 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@xxxxxxxxxxxxxx>
>> Reviewed-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
>> ---
>>
>> (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
>> +
> 
> Should CONFIG_TYPEC_DP_ALTMODE select this one? Otherwise, we need to do it
> manually.
> 
> $ grep -nr --include=Kconfig "select DRM_AUX_HPD_BRIDGE" .
> ./drivers/soc/qcom/Kconfig:118: select DRM_AUX_HPD_BRIDGE
> ./drivers/usb/typec/ucsi/Kconfig:88:    select DRM_AUX_HPD_BRIDGE if DRM_BRIDGE && OF
> ./drivers/usb/typec/ucsi/Kconfig:99:    select DRM_AUX_HPD_BRIDGE if DRM_BRIDGE && OF
> ./drivers/usb/typec/tcpm/Kconfig:62:    select DRM_AUX_HPD_BRIDGE if DRM_BRIDGE && OF
> ./drivers/usb/typec/tcpm/Kconfig:85:    select DRM_AUX_HPD_BRIDGE if DRM_BRIDGE && OF
> 

That's a fair point. But based on the previous discussion, Heikki
point out that configurations in the TYPEC subsystem should not
select configurations from DRM.

-- 
Best, 
Chaoyi