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From:   Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Date:   Thu, 3 Aug 2023 18:36:23 +0300
Message-ID: <CAA8EJppCECObEe5UG3LsHUsmYfKzakWzVw33S4nVc=DB9sA0ig@mail.gmail.com>
Subject: Re: [PATCH 3/4] drm/uapi: document the USB subconnector type
To:     Simon Ser <contact@emersion.fr>
Cc:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andrzej Hajda <andrzej.hajda@intel.com>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Robert Foss <rfoss@kernel.org>,
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        Bjorn Andersson <andersson@kernel.org>,
        Konrad Dybcio <konrad.dybcio@linaro.org>,
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        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
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On Thu, 3 Aug 2023 at 18:31, Simon Ser <contact@emersion.fr> wrote:
>
> On Thursday, August 3rd, 2023 at 17:22, Simon Ser <contact@emersion.fr> w=
rote:
>
> > 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 =E2=86=92 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.

If we want to make it different from GUD, we might want to define a
USB-DP connector type (which would also include SlimPort).

>
> However, in the USB-C case, DP itself is tunneled inside USB-C. And you
> might use a USB-C =E2=86=92 DP adapter. So it's not really *sub*connector=
, it's
> more of a *super*connector, right?
>
> I think [1] is somewhat related, since it also allows user-space to
> discover whether a connector uses USB-C. But relying on sysfs to figure
> this out isn't super optimal perhaps.
>
> [1]: https://lore.kernel.org/dri-devel/20221108185004.2263578-1-wonchung@=
google.com/


--=20
With best wishes
Dmitry