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

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Message-ID: <CA+E=qVeDpLqAM6Qsd6oHfeYHB_JHdSb5GtY7i994GT5_RW4_Bg@mail.gmail.com>
Date:   Mon, 15 Jul 2019 17:28:53 -0700
From:   Vasily Khoruzhick <anarsoul@...il.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Andrzej Hajda <a.hajda@...sung.com>, Torsten Duwe <duwe@....de>,
        Harald Geyer <harald@...ib.org>, 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 Fri, Jul 12, 2019 at 1:15 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
>
> On Wed, Jul 10, 2019 at 03:11:04PM -0700, Vasily Khoruzhick wrote:
> > On Wed, Jul 10, 2019 at 4:40 AM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
> > > > > > There's another issue: if we introduce edp-connector we'll have to
> > > > > > specify power up delays somewhere (in dts? or in platform driver?), so
> > > > > > edp-connector doesn't really solve the issue of multiple panels with
> > > > > > same motherboard.
> > > > >
> > > > > And that's what that compatible is about :)
> > > >
> > > > Sorry, I fail to see how it would be different from using existing
> > > > panels infrastructure and different panels compatibles. I think Rob's
> > > > idea was to introduce generic edp-connector.
> > >
> > > Again, there's no such thing as a generic edp-connector. The spec
> > > doesn't define anything related to the power sequence for example.
> > >
> > > > If we can't make it generic then let's use panel infrastructure.
> > >
> > > Which uses a device specific compatible. Really, I'm not sure what
> > > your objection and / or argument is here.
> > >
> > > In addition, when that was brought up in the discussion, you rejected
> > > it because it was inconvenient:
> > > https://patchwork.freedesktop.org/patch/283012/?series=56163&rev=1#comment_535206
> >
> > It is inconvenient, but I don't understand how having board-specific
> > connectors fixes it.
>
> How it would not fix it?

I think I got your idea, but yet I think it's not the best solution.

Do I understand correctly that you're proposing to introduce
board-specific edp-connector driver that will be aware of worst case
power up delays and will control backlight and power?

Then why not to add another board-specific panel (e.g.
"pine64,pinebook-panel") to simple-panel.c that does the same?

> You'll have one connector, without the need to describe each and every
> panel in the device tree and rely on the EDID instead, and you'll have
> the option to power up the regulator you need.
>
> I really don't understand what's the issue here, so let's take a step
> back. What are is the issue , what are your requirements, and how
> would you like that to be described ?

We have a device (Pinebook) that uses the same board with multiple edp
panels. So far there're pinebooks with 3 different panels: 11" with
768p panel, 11" with 1080p panel, 14" with 768p panel.

Currently there's no way to describe all pinebooks with a single dts.
There's a simple workaround though -- we can just specify a panel with
worst power up delays in dts and it'll work since anx6345 driver
ignores panel modes anyway and uses EDID.

Originally I proposed to extend simple-panel driver to support generic
edp-panel but it was rejected. I still believe that it's the best
solution assuming we can specify delays in dts, since panels list is
specific to particular device and it probably can't be reused, i.e.
there's no good reason to move it into C code.

Rob Herring proposed to introduce edp-connector. While I still believe
that it's not accurate description of hardware since it'll have to
have backlight node (backlight is actually panel property) I was OK
with this approach assuming we can store delays in dts.

Later it evolved into board-specific edp-connector.

So far I don't understand why everyone is trying to avoid introducing
edp-panel driver that can read delays from dts. Basically, I don't
understand what's the magic behind simple-panel.c and why new panels
should be added there rather than described in dts. [1] Doesn't
explain that.

[1] http://sietch-tagr.blogspot.com/2016/04/display-panels-are-not-special.html

Regards,
Vasily

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