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

[Xu Yang]

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.

Thanks,
Xu Yang