linux-kernel - Re: [PATCH 3/4] drm/uapi: document the USB subconnector type

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Date:   Thu, 3 Aug 2023 23:57:27 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Simon Ser <contact@...rsion.fr>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Janne Grunau <j@...nau.net>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org
Subject: Re: [PATCH 3/4] drm/uapi: document the USB subconnector type

On Thu, 3 Aug 2023 at 23:47, Simon Ser <contact@...rsion.fr> wrote:
>
> On Thursday, August 3rd, 2023 at 22:44, Laurent Pinchart <laurent.pinchart@...asonboard.com> wrote:
>
> > On Thu, Aug 03, 2023 at 03:31:16PM +0000, Simon Ser wrote:
> >
> > > On Thursday, August 3rd, 2023 at 17:22, Simon Ser contact@...rsion.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.
> >
> > Doesn't this contradict the example use case you gave in your previous
> > e-mail, with wlroots stating "DP-3 via DVI-D" ? I understand that as DP
> > carried over a DVI-D physical connector, did I get it wrong ?
>
> No, this is DVI carried over DP. DP cannot be carried over VGA/DVI/HDMI,
> but VGA/DVI/HDMI can be carried over DP.

Well, not quite. It means that the sink (display) connected to this
port identifies itself as an VGA / DVI / HDMI monitor.
E.g. on if connect HDMI/DVI monitor through the DP-DVI dongle (native
DP connector), AMD driver still identifies it as 'subconnector HDMI',
despite dongle a DVI connector on the other side.

-- 
With best wishes
Dmitry