linux-kernel - Re: [PATCH v2 7/7] arm64: dts: allwinner: a64: enable ANX6345 bridge on Teres-I

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Date:   Mon, 1 Jul 2019 11:58:42 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Andrzej Hajda <a.hajda@...sung.com>
Cc:     Torsten Duwe <duwe@....de>, Harald Geyer <harald@...ib.org>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Icenowy Zheng <icenowy@...c.io>,
        Sean Paul <seanpaul@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree <devicetree@...r.kernel.org>,
        arm-linux <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 7/7] arm64: dts: allwinner: a64: enable ANX6345 bridge
 on Teres-I

Hi!

On Fri, Jun 28, 2019 at 12:39:32PM +0200, Andrzej Hajda wrote:
> On 12.06.2019 17:20, Maxime Ripard wrote:
> >> I am not sure if I understand whole discussion here, but I also do not
> >> understand whole edp-connector thing.
> > The context is this one:
> > https://patchwork.freedesktop.org/patch/257352/?series=51182&rev=1
> > https://patchwork.freedesktop.org/patch/283012/?series=56163&rev=1
> > https://patchwork.freedesktop.org/patch/286468/?series=56776&rev=2
> >
> > TL;DR: This bridge is being used on ARM laptops that can come with
> > different eDP panels. Some of these panels require a regulator to be
> > enabled for the panel to work, and this is obviously something that
> > should be in the DT.
> >
> > However, we can't really describe the panel itself, since the vendor
> > uses several of them and just relies on the eDP bus to do its job at
> > retrieving the EDIDs. A generic panel isn't really working either
> > since that would mean having a generic behaviour for all the panels
> > connected to that bus, which isn't there either.
> >
> > The connector allows to expose this nicely.
>
> As VESA presentation says[1] eDP is based on DP but is much more
> flexible, it is up to integrator (!!!) how the connection, power
> up/down, initialization sequence should be performed. Trying to cover
> every such case in edp-connector seems to me similar to panel-simple
> attempt failure. Moreover there is no such thing as physical standard
> eDP connector. Till now I though DT connector should describe physical
> connector on the device, now I am lost, are there some DT bindings
> guidelines about definition of a connector?

This might be semantics but I guess we're in some kind of grey area?

Like, for eDP, if it's soldered I guess we could say that there's no
connector. But what happens if for some other board, that signal is
routed through a ribbon?

You could argue that there's no physical connector in both cases, or
that there's one in both, or one for the ribbon and no connector for
the one soldered in.

> Maybe instead of edp-connector one would introduce integrator's specific
> connector, for example with compatible "olimex,teres-edp-connector"
> which should follow edp abstract connector rules? This will be at least
> consistent with below presentation[1] - eDP requirements depends on
> integrator. Then if olimex has standard way of dealing with panels
> present in olimex/teres platforms the driver would then create
> drm_panel/drm_connector/drm_bridge(?) according to these rules, I guess.
> Anyway it still looks fishy for me :), maybe because I am not
> familiarized with details of these platforms.

That makes sense yes

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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