linux-kernel - Re: [PATCH v3 0/5] Add generic-display-mux driver and bindings

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Date:   Thu, 30 Mar 2023 12:11:18 +0800
From:   Chen-Yu Tsai <wenst@...omium.org>
To:     Jagan Teki <jagan@...rulasolutions.com>
Cc:     Pin-yen Lin <treapking@...omium.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Robert Foss <rfoss@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jonas Karlman <jonas@...boo.se>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        linux-mediatek@...ts.infradead.org,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        chrome-platform@...ts.linux.dev,
        Guenter Roeck <groeck@...omium.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 0/5] Add generic-display-mux driver and bindings

On Thu, Mar 30, 2023 at 2:10 AM Jagan Teki <jagan@...rulasolutions.com> wrote:
>
> On Sat, Feb 18, 2023 at 4:47 PM Pin-yen Lin <treapking@...omium.org> wrote:
> >
> > This series is developed for and tested on MT8173 board, and the layout is:
> >
> >                                   /-- anx7688
> > -- MT8173 HDMI bridge -- GPIO mux
> >                                   \-- native HDMI
>
> What is the part number of this GPIO mux? Does mux gpio interrupt
> based and able to switch output HDMI and DP. If so, how this gpio
> interrupt is different than the HPD in native HDMI? I mean does HPD
> have any detection bottlenecks with mux gpio interrupt?

It's a full blown HDMI 1:2 demultiplexer, so DDC and HPD signals are muxed
as well. The anx7688 handles all the Type-C stuff, and our EC talks to it.
If HDMI output from the SoC needs to be muxed over for DP alt-mode, the EC
will signal the SoC.

> I do have GPIO Mux that input DSI and two outputs DMD/HDMI Input and
> HDMI Out. 2x1 with 1x2 mux.
>
> I'm thinking having a generic mux to select the specific out number of
> outputs with associated interface outputs can be a viable solution to
> address all use cases here.

AFAIK DRM doesn't allow dynamically changing the constitution of a display
pipeline, so it doesn't really work out for us.

If you're just muxing between different outputs with passive/dumb bridges,
it may still work for you.

ChenYu