linux-kernel - Re: [PATCH v5 6/9] dt/bindings: drm/bridge: it6505: Add mode-switch support

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Message-ID: <CACeCKaem-b5ePtkeR2njS9ZgX3Ez1GViArPxS92fk7eF0=NmFA@mail.gmail.com>
Date:   Thu, 23 Jun 2022 12:15:42 -0700
From:   Prashant Malani <pmalani@...omium.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        bleung@...omium.org, heikki.krogerus@...ux.intel.com,
        Pin-Yen Lin <treapking@...omium.org>,
        Allen Chen <allen.chen@....com.tw>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>, devicetree@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>,
        José Expósito <jose.exposito89@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Maxime Ripard <maxime@...no.tech>,
        Neil Armstrong <narmstrong@...libre.com>,
        Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>, Robert Foss <robert.foss@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Xin Ji <xji@...logixsemi.com>
Subject: Re: [PATCH v5 6/9] dt/bindings: drm/bridge: it6505: Add mode-switch support

On Thu, Jun 23, 2022 at 12:08 PM Stephen Boyd <swboyd@...omium.org> wrote:
>
> Quoting Prashant Malani (2022-06-23 11:37:08)
> > On Thu, Jun 23, 2022 at 11:24 AM Stephen Boyd <swboyd@...omium.org> wrote:
> > >
> > > Quoting Prashant Malani (2022-06-22 10:34:35)
> > > > From: Pin-Yen Lin <treapking@...omium.org>
> > > >
> > > > ITE IT6505 can be used in systems to switch USB Type-C DisplayPort
> > > > alternate mode lane traffic between 2 Type-C ports.
> > >
> > > How does it work? From what I can tell from the information I find when
> > > googling this part[1] and looking at the existing binding doc is that
> > > this device is a DPI to DP bridge, and it outputs DP (probably 4 lanes
> > > of it?). Does the 2 type-c port design work by transmitting DP on two
> > > lanes of DP for one type-c port and another two lanes of DP for the
> > > other type-c port?
> > >
> > > DP could be one lane, so if this device is able to output one lane on
> > > any output differential pair then I suspect it could support 4 type-c
> > > ports if the hardware engineer connected it that way. Can you confirm my
> > > suspicion?
> >
> > I will let Pin-Yen comment re: this hardware, but 1-lane DP is not a
> > supported Type-C Pin assignment
> > (as per VESA DP Alternate Mode Spec version 2.0 [2]), so the H/W
>
> Some missing link?

My bad. I tried to find a publicly accessible link to the DP altmode
spec, but it
seems like one needs to be a VESA member to access it :/

>
> > configuration you are suggesting shouldn't be possible.
> >
>
> Alright, cool. But it is possible in the DP spec. So it seems like if
> this is connected to 4 DP connectors it could be used to mux between DP
> on 4 DP ports.

Ack. In that case, no "typec-switches" should be added to the DT.