linux-kernel - Re: [PATCH 4/4] arm64: DTS: allwinner: a64: enable ANX6345 bridge on Teres-I

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Message-ID: <CA+E=qVe5NkAvHXPvVc7iTbZn5sKeoRm0166zPW_s83c2gk7B+g@mail.gmail.com>
Date:   Thu, 16 May 2019 09:06:41 -0700
From:   Vasily Khoruzhick <anarsoul@...il.com>
To:     Torsten Duwe <duwe@....de>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Icenowy Zheng <icenowy@...c.io>,
        Sean Paul <seanpaul@...omium.org>,
        Harald Geyer <harald@...ib.org>,
        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 4/4] arm64: DTS: allwinner: a64: enable ANX6345 bridge on Teres-I

On Thu, May 16, 2019 at 8:48 AM Torsten Duwe <duwe@....de> wrote:
>
> On Wed, May 15, 2019 at 08:08:57AM -0700, Vasily Khoruzhick wrote:
> > On Wed, May 15, 2019 at 12:32 AM Torsten Duwe <duwe@....de> wrote:
> > >
> > > It does comply with the bindings. The ports are all optional.
> > > As far as DT is concerned, the signal path ends here. This is also the
> > > final component _required_ to get the Linux kernel DRI up and running.
> >
> > Ugh, then bindings should be fixed. It's not optional. It may work if
> > bootloader enables power for you, but it won't if you disable display
> > driver in u-boot.
>
> I double-checked. On the Teres-I, mentioning the panel _is_ optional.

It's not. See power on sequence in
https://www.olimex.com/Products/DIY-Laptop/SPARE-PARTS/TERES-015-LCD11-6/resources/N116BGE-EA2.pdf

Driver can talk to the panel over AUX channel only after t1+t3, t1 is
up to 10ms, t3 is up to 200ms. It works with older version of driver
that keeps panel always on because it takes a while between driver
probe and pipeline start.

It'll likely break with newer version of driver that turns on panel
only when bridge is active. You'll see AUX timeouts - it won't be able
to probe EDID in some cases. Problem can be intermittent and device
dependent.

All in all - you don't need panel timings since there's EDID but you
still need panel delays. Anyway, it's up to you and maintainers.

> PD23 powers down panel and backlight as much as possible, see
> 24bd5d2cb93bc arm64: dts: allwinner: a64: teres-i: enable backlight
> (currently only in Maxime's repo) and the Teres-I schematics...
>
> And the driver in your repo neatly guards all accesses with
> "if (anx6345->panel)" -- good!
> But I found the Vdds are required, so I added them as such.
>
> > I guess you're testing it with older version of anx6345. Newer version
> > that supports power management [1] needs startup delay for panel.
> > Another issue that you're seeing is that backlight is not disabled on
> > DPMS events. All in all, you need to describe panel in dts.
> >
> > [1] https://github.com/anarsoul/linux-2.6/commit/2fbf9c242419c8bda698e8331a02d4312143ae2c
>
> > > Should I also have added a Tested-by: ? ;-)
> >
> > I don't have Teres, so I haven't tested these.
>
> *I* have one, and this works. I'll retest with your newer driver,
> just in case. Nonetheless, the changes in this series should be fine.
> Sending out v2 in a moment...
>
>         Torsten
>