linux-kernel - Re: [PATCH v5 5/9] drm/bridge: anx7625: Add typec_mux

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Date:   Tue, 28 Jun 2022 15:40:44 -0500
From:   Stephen Boyd <swboyd@...omium.org>
To:     Prashant Malani <pmalani@...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>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Nícolas F . R . A . Prado 
        <nfraprado@...labora.com>, Allen Chen <allen.chen@....com.tw>,
        Andrzej Hajda <andrzej.hajda@...el.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>,
        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 5/9] drm/bridge: anx7625: Add typec_mux_set callback function

Quoting Prashant Malani (2022-06-28 12:48:11)
> On Tue, Jun 28, 2022 at 12:25 PM Stephen Boyd <swboyd@...omium.org> wrote:
> >
> > Quoting Prashant Malani (2022-06-22 10:34:34)
> > > diff --git a/drivers/gpu/drm/bridge/analogix/anx7625.c b/drivers/gpu/drm/bridge/analogix/anx7625.c
> > > index bd21f159b973..5992fc8beeeb 100644
> > > --- a/drivers/gpu/drm/bridge/analogix/anx7625.c
> > > +++ b/drivers/gpu/drm/bridge/analogix/anx7625.c
[..]
> > > +
> > > +       if (ctx->num_typec_switches == 1)
> >
> > How do we handle the case where the usb-c-connector is directly
> > connected to the RX1/TX1 and RX2/TX2 pins? This device would be an
> > orientation (normal/reverse) and mode switch (usb/dp) in that scenario,
> > but this code is written in a way that the orientation switch isn't
> > going to flip the crosspoint switch for the different pin assignments.
>
> If all 4 SS lanes are connected to 1 usb-c-connector; there would be
> just 1 "typec-switch" node.
> In that case, the DT would only specify it as an "orientation-switch"
> and register
> an orientation-switch with the Type-C framework. The orientation switch would
> pretty much do what the mode-switch callback does here (configuring
> the crosspoint
> switch).
> One could also register a "mode-switch" there but it wouldn't do
> anything (all 4 lanes are already
> connected so there is nothing to re-route in the crosspoint switch).
> Hence the above "if" check.

Would we still want to route the DP traffic out if the pin assignment
didn't have DP? Does the hardware support some mode where the DP traffic
is shutdown? Or maybe the HPD pin needs to be quieted unless DP is
assigned?

I suppose none of those things matter though as long as there is some
typec switch registered here so that the driver can be informed of the
pin assignment. Is it right that the "mode-switch" property is only
required in DT if this device is going to control the mode of the
connector, i.e. USB+DP, or just DP? Where this device can't do that
because it doesn't support only DP.

>
> Unfortunately, I don't have hardware which connects all 4 SS lanes
> from 1 Type-C port
> to the anx7625, so I didn't add the orientation switch handling to the
> driver (since I have no way of verifying it).

Alright. Maybe add a TODO then so it's more obvious that orientation
isn't handled.

>
> Regarding DP alt-mode pin assignments : I think anx7625 will only support Pin D
> (only 2 lane DP, no 4 lane DP).
>

Makes sense. Thanks!