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

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Message-ID: <ADjuOeqA6575DKutMPaR9mW9rLhm-wjLc4ruoUkNwImf-GB90FdwDB7v7y6LFdzVG3BC4R52A0RUtStK4_smmGYTUs3UPDOX4T4Zl2YHkxE=@emersion.fr>
Date:   Thu, 03 Aug 2023 15:31:16 +0000
From:   Simon Ser <contact@...rsion.fr>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
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 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.

However, in the USB-C case, DP itself is tunneled inside USB-C. And you
might use a USB-C → 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/