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

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Date:   Thu, 03 Aug 2023 15:43:25 +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 17:36, Dmitry Baryshkov <dmitry.baryshkov@...aro.org> wrote:

> On Thu, 3 Aug 2023 at 18:31, Simon Ser contact@...rsion.fr 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.
> 
> 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.
- 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).