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

[Chaoyi Chen]

Hello Xu Yang, Heikki

On 6/29/2026 4:26 PM, Xu Yang wrote:
> On Mon, Jun 29, 2026 at 09:29:08AM +0800, Chaoyi Chen wrote:
>> 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.
> 
> I have just reviewed your previous patchsets but I did't find such opinion from
> Heikki. Otherwise, why are tcpm.c/ucsi.c already allowed to add the above select
> condition in their configs?
> 
> I think Heikki means that the DRM_AUX_HPD_BRIDGE shouldn't been selected at the
> top level of Type-C subsystem. Because not all Type-C devices support the DP function.
> 
> As a generic Type-C DP HPD bridge, displayport.c will likely need to use it in
> the future. Therefore, allowing displayport.c to select DRM_AUX_HPD_BRIDGE makes sense.
> 
> According to my testing, it's impossible to build this driver in unless TYPEC_FUSB302
> or a relevant CONFIG is built in to select DRM_AUX_HPD_BRIDGE, or the defconfig is modified.
> 

Yep. For me, I select DRM_AUX_HPD_BRIDGE in DRM.

@Heikki, what do you think of the following change?
Should we add a new patch for this? Thanks.


diff --git a/drivers/usb/typec/altmodes/Kconfig b/drivers/usb/typec/altmodes/Kconfig
index 7867fa7c405d..f89cdf3c949b 100644
--- a/drivers/usb/typec/altmodes/Kconfig
+++ b/drivers/usb/typec/altmodes/Kconfig
@@ -5,6 +5,7 @@ menu "USB Type-C Alternate Mode drivers"
 config TYPEC_DP_ALTMODE
        tristate "DisplayPort Alternate Mode driver"
        depends on DRM
+       select DRM_AUX_HPD_BRIDGE 
        help
          DisplayPort USB Type-C Alternate Mode allows DisplayPort
          displays and adapters to be attached to the USB Type-C

-- 
Best, 
Chaoyi