[PATCH 3/4] drm/uapi: document the USB subconnector type

[Dmitry Baryshkov]

On Thu, 3 Aug 2023 at 18:43, Simon Ser <contact at emersion.fr> wrote:
>
> On Thursday, August 3rd, 2023 at 17:36, Dmitry Baryshkov <dmitry.baryshkov at linaro.org> wrote:
>
> > On Thu, 3 Aug 2023 at 18:31, Simon Ser contact at emersion.fr wrote:
> >
> > > On Thursday, August 3rd, 2023 at 17:22, Simon Ser contact at emersion.fr wrote:
> > >
> > > > The KMS docs describe "subconnector" to be defined as "downstream port" for DP.
> > > > Can USB-C (or USB) be seen as a DP downstream port?
> > >
> > > To expand on this a bit: I'm wondering if we're mixing apples and
> > > oranges here. The current values of "subconnector" typically describe
> > > the lower-level protocol tunneled inside DP. For instance, VGA can be
> > > tunneled inside the DP cable when using DP → VGA adapter.
> >
> > My opinion hasn't changed: I think this should be the USB connector
> > with proper DP / DVI / HDMI / etc. subconnector type (or lack of it).
> > In the end, the physical connector on the side of laptop is USB-C.
>
> - Even if the connector is USB-C, the protocol used for display is
>   still DP. There's also the case of Thunderbolt.

Yes. But the connector type is not about the protocol.

> - This is inconsistent with existing drivers. i915 and amdgpu expose
>   DP ports for their USB-C ports. Changing that isn't possible without
>   causing user-space regressions (compositor config files use the
>   connector type).

Yes, I know. Consider my phrase as a personal opinion or minority report.

I think that using DisplayPort for USB-C connectors was a mistake,
which we now have to cope with somehow.

-- 
With best wishes
Dmitry