linux-kernel - Re: [RFC PATCH v1 00/12] drm,usb/typec: uABI for USB-C DisplayPort connectors

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Message-ID: <11765348-1d5c-41aa-babc-7c6da68cd9f1@linaro.org>
Date:   Mon, 4 Sep 2023 18:49:02 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Bjorn Andersson <andersson@...nel.org>
Cc:     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>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Janne Grunau <j@...nau.net>, Simon Ser <contact@...rsion.fr>,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        freedreno@...ts.freedesktop.org
Subject: Re: [RFC PATCH v1 00/12] drm,usb/typec: uABI for USB-C DisplayPort
 connectors

On 04/09/2023 18:46, Bjorn Andersson wrote:
> On Mon, Sep 04, 2023 at 12:41:38AM +0300, Dmitry Baryshkov wrote:
>> During the discussion regarding DisplayPort wrapped in the USB-C
>> connectors (via the USB-C altmode) it was pointed out that currently
>> there is no good way to let userspace know if the DRM connector in
>> question is the 'native' DP connector or if it is the USB-C connector.
>>
>> An attempt to use DRM_MODE_CONNECTOR_USB for such connectors was
>> declined, as existing DP drivers (i915, AMD) use
>> DRM_MODE_CONNECTOR_DisplayPort. New drivers should behave in the same
>> way.
>>
> 
> Sorry, didn't see the commit message before posting my complaint about
> USB -> DisplayPort.
> 
>> An attempt to use subconnector property was also declined. It is defined
>> to the type of the DP dongle connector rather than the host connector.
>>
>> This attempt targets reusing the connector's PATH property. Currently
>> this property is only used for the DP MST connectors. This patchset
>> reuses it to point out to the corresponding registered typec port
>> device.
>>
> 
> Still interested in understanding how the path string should look like.

As wrote in the other letter, on RB5 it is 'typec:port0'. If the machine 
has two Type-C ports and two connected DP blocks, one of them will have 
'typec:port0', another one 'typec:port1'. This way one can further look 
under /sys/class/typec/portN/physical_localtion/ and find corresponding 
location, etc.

> Is the path expected to be consumed by machine, or is it only there for
> human convenience?

As with DP MST it is expected that userspace will consume this 
information, possibly renaming the connector. For example, on my laptop 
I have DP-1, ... DP-5 connectors (with DP-2 -- DP-5 being DP MST ones). 
Xorg renames them to DP-1, DP-2, DP-1-1, DP-1-2, DP-1-3, because the MST 
ones are branches for the DP-1.

-- 
With best wishes
Dmitry