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

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Date:   Fri, 28 Jun 2019 12:39:32 +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

Hi Maxime,

It seems I have missed your response.

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?

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.

[1]: https://www.vesa.org/wp-content/uploads/2010/12/DisplayPort-DevCon-Presentation-eDP-Dec-2010-v3.pdf

>
>> According to VESA[1] eDP is "Internal display interface" - there is no
>> external connector for eDP, the way it is connected is integrator's
>> decision, but it is fixed - ie end user do not plug/unplug it.
> I'm not sure if you mean DRM or DT connector here though. In DRM,
> we're doing this all the time for panels. I'm literaly typing this
> from a laptop that has a screen with an eDP connector.

VESA describes only hardware, but since DT also describes hardware I
guess it should be similar.

Regards

Andrzej

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