linux-kernel - Re: [PATCH] drm/bridge: anx7625: Add anx7625 port switching.

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Message-ID: <CANdKZ0cGXkcVfevpT4y_za5vu_y0s-NdCvhw1AVibK-q_W8yBw@mail.gmail.com>
Date:   Thu, 12 Nov 2020 17:07:05 +0800
From:   Pi-Hsun Shih <pihsun@...omium.org>
To:     Prashant Malani <pmalani@...omium.org>
Cc:     Nicolas Boichat <drinkcat@...omium.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Xin Ji <xji@...logixsemi.com>,
        Sam Ravnborg <sam@...nborg.org>,
        "open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>,
        heikki.krogerus@...ux.intel.com
Subject: Re: [PATCH] drm/bridge: anx7625: Add anx7625 port switching.

Hi Prashant,

Please see inline reply as below.

On Thu, Nov 12, 2020 at 4:59 PM Prashant Malani <pmalani@...omium.org> wrote:
>
> Hi Pi-Hsun,
>
> I haven't gone through the code, but did have a high-level comment
> (kindly see inline)
>
> On Thu, Nov 12, 2020 at 02:40:40PM +0800, Pi-Hsun Shih wrote:
> > When output 2 lanes DP data, anx7625 can output to either TX1/RX1 or
> > TX2/RX2. In typical usage, these two TX/RX pairs corresponds to two
> > orientations of typec.
> >
> > On some board one anx7625 is used as DPI to DP converter for two typec
> > ports. In this case, the TX1/RX1 and TX2/RX2 are connected to two usb
> > muxes, which mux the DP data with the rest of the USB3 data, and
> > connects to the two typec ports.
> >
> > This patch adds option for anx7625 to acts as a usb typec switch and
> > switch output lanes based on the typec orientation, or acts as two usb
> > typec mux and switch output lanes depending on whether the two ports
> > currently has DP enabled.
> >
> > Signed-off-by: Pi-Hsun Shih <pihsun@...omium.org>
> >
> > ====================================================================
> >
> > This is an attempt to use typec framework with how we're using anx7625
> > on Chrome OS asurada board.
> >
> > An example of the dts for the two ports case can be found at
> > https://crrev.com/c/2507199/6
>
> Do you plan on submitting DT schemas & bindings documentation for the switch(es)
> that are intended to be used?

Yes I plan to submit corresponding DT schemas & bindings documentation
changes if this change looks good.

>
> I would strongly recommend that for usb-c-connector since AFAIK they don't exist, and
> I don't believe there is explicit support for them in the Type C connector class framework
> (even .
>
> IMO this would be needed to ensure an implementation here doesn't break
> in the event of modifications to the connector class framework (or Type
> C port drivers like cros-ec-typec) in the future. I think some patches
> were floated for this for orientation switch [1] so those might provide
> some hints about how to proceed.
>
> I've CC-ed Heikki (Type C maintainer) in case he has additional comments regarding this.
>
> >
> > Sending this as a RFC patch since I'm not sure about the best approach
> > here. Should the logic of switching output lanes depends on ports be
> > coupled inside anx7625 driver, or in another driver, or is there
> > any existing way to accomplish this?
>
> Might be good to add [RFC] as a tag instead of [PATCH] in case this
> iteration is chiefly to solicit comments.

Ah I did have [RFC] tag in some local .patch files before. I guess I
somehow forgot it in later `git format-patch` runs...
I'll add the tag in the next version, thanks for the comments.

>
> Best regards,
>
> -Prashant
>
> [1]:
> https://lore.kernel.org/linux-usb/1604403610-16577-1-git-send-email-jun.li@nxp.com/
> >