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

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Date:   Fri, 17 May 2019 11:08:45 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Torsten Duwe <duwe@....de>
Cc:     Vasily Khoruzhick <anarsoul@...il.com>,
        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>,
        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 Fri, May 17, 2019 at 10:14:18AM +0200, Torsten Duwe wrote:
> On Fri, 17 May 2019 09:27:38 +0200
> Maxime Ripard <maxime.ripard@...tlin.com> wrote:
>
> > On Thu, May 16, 2019 at 06:48:59PM +0200, Torsten Duwe wrote:
> > > On Thu, May 16, 2019 at 09:06:41AM -0700, Vasily Khoruzhick wrote:
> > > >
> > > > Driver can talk to the panel over AUX channel only after t1+t3,
> > > > t1 is up to 10ms, t3 is up to 200ms.
> > >
> > > This is after power-on. The boot loader needs to deal with this.
> >
> > The bootloader can deal with it, but the kernel will also need to. The
> > bootloader might not be doing this because it's not been updated, the
> > regulator might have been disabled between the time the kernel was
> > started and the time the bridge driver probes, etc.
>
> No, you cannot practically switch off this voltage. It supports _all_
> the devices I mentioned. In fact, the PMIC needs to enable it initially,
> and then it takes some time before the SoC can access the MMC and read
> the SPL from it, just because of exactly these 3.3V. Then the boot
> loader starts, and later the eDP bridge gets initialised.

All these devices can be unused, disabled, or compiled as modules.

> In *theory*, albeit a very daring one, I could imagine a very deep
> sleep mode that can only be ended by pressing the power button, which
> should still work without DCDC1. Only then, a description of the panel
> would be required. But I probably missed something and even this does
> not work.
>
> So for all current practical purposes, we can assume the Teres-I panel
> to be powered properly and providing valid EDID; nothing to worry about
> in software.

You're creating a generic binding for all the users of that bridge,
while considering only the specific case of the Teres-I.

Maxime

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

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