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

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Message-ID: <64471471-5b4d-3c1f-a0e3-e02ee78ca23c@samsung.com>
Date:   Mon, 1 Jul 2019 14:27:51 +0200
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Maxime Ripard <maxime.ripard@...tlin.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

On 01.07.2019 11:58, Maxime Ripard wrote:
> 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.


This is not about ribbon vs soldering. It is about usage: this
connection is static across the whole life of the device (except
exceptional things: repair, non-standard usage, etc).

And "the real connector" is (at least for me) something where end-user
can connect/disconnect different things: USB, HDMI, ethernet, etc. And
obviously to be functional it should be somehow standardized. So even if
there could be some grey area, I do not see it here.


>
>> 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


And what if some panel can be used with this pseudo-connecter and in
some different hw directly? Code duplication? DT overlays?


Regards

Andrzej


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