linux-kernel - Re: [PATCH] drm/bridge: fix anx6345 power up sequence

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Date:   Sat, 21 May 2022 08:28:27 -0700
From:   Vasily Khoruzhick <anarsoul@...il.com>
To:     Torsten Duwe <duwe@....de>
Cc:     Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thierry Reding <treding@...dia.com>,
        Lyude Paul <lyude@...hat.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Harald Geyer <harald@...ib.org>, stable@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: fix anx6345 power up sequence

On Thu, May 19, 2022 at 6:40 AM Torsten Duwe <duwe@....de> wrote:
>
> On Wed, 18 May 2022 09:53:58 -0700
> Vasily Khoruzhick <anarsoul@...il.com> wrote:
>
> > On Thu, Apr 28, 2022 at 8:58 AM Torsten Duwe <duwe@....de> wrote:
>
> > > power on the eDP bridge? Could there be any leftovers from that
> > > mechanism? I use a hacked-up U-Boot with a procedure similar to the
> > > kernel driver as fixed by this change.
>
> I was asking because I recall an ugly hack in some ATF code to power up
> the chip correctly. Did you patch ATF, and maybe call functions of it
> at runtime?

Initially it's powered on by ATF on system power up. ATF parses DTB
and finds the regulators that it needs to enable and enables them.
It's done in ATF because u-boot SPL didn't have enough space to fit in
the AXP803 driver. It's only done at startup and once linux takes
over, ATF doesn't touch these regulators.

> > >
> > > But the main question is: does this patch in any way worsen the
> > > situation on the pinebook?
> >
> > I don't think it worsens anything, but according to the datasheet the
> > change makes no sense. Could you try increasing T2 instead of changing
> > the power sequence?
>
> According to the datasheet, there is also T3, I realise now. The
> diagram talks about "System Clock", but both Teres and Pinebook have a
> passive resonator circuit there. Correct me if I'm wrong, but without
> chip power, there is little to resonate. What if that driving clock
> circuit is powered by Vdd25? Maybe the earlier provision of 2V5 is
> enough for Teres' Q4, but Pinebook X4 takes even longer? The start-up
> times can be in the range of milliseconds.

That's plausible, but can you please try just increasing the delays
without changing the power sequence?

>         Torsten