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

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Date:   Thu, 03 Aug 2023 15:22:05 +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 Wednesday, August 2nd, 2023 at 21:23, Dmitry Baryshkov <dmitry.baryshkov@...aro.org> wrote:

> >> >> +	{ DRM_MODE_SUBCONNECTOR_USB,	     "USB"       }, /* DP */
> >> >
> >> > Should this be DRM_MODE_SUBCONNECTOR_USB_C and "USB-C", in case we get
> >> > another USB type later ?
> >>
> >> Hmm, which id should I use for micro-USB then? (consider anx7808,
> >> SlimPort). I thought about using DRM_MODE_SUBCONNECTOR_USB for both of
> >> them. But maybe I should add another subtype for SlimPort.
> >
> >I suppose it depends on whether userspace needs a way to differentiate
> >those. Do you have a good visibility on the userspace use cases ?
> 
> No. I'm not even sure, which userspace handles subtypes properly.

wlroots uses it for human-readable output descriptions, e.g.

    > wayland-info
    interface: 'wl_output',                                  version:  4, name: 49
    	name: DP-3
    	description: Samsung Electric Company SyncMaster HS3P505873 (DP-3 via DVI-D)

The "via DVI-D" bit comes from subconnector.

The description is displayed to the user when picking an output to screen
capture, among other things. It is helpful to users because they can better
understand why their output connected via DVI shows up as "DP".

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?