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

From: Maxime Ripard <maxime.ripard@bootlin.com>
To: Torsten Duwe <duwe@lst.de>
Cc: Mark Rutland <mark.rutland@arm.com>,
	devicetree <devicetree@vger.kernel.org>,
	David Airlie <airlied@linux.ie>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Andrzej Hajda <a.hajda@samsung.com>, Chen-Yu Tsai <wens@csie.org>,
	Rob Herring <robh+dt@kernel.org>,
	Thierry Reding <thierry.reding@gmail.com>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	Daniel Vetter <daniel@ffwll.ch>, Harald Geyer <harald@ccbib.org>,
	Sean Paul <seanpaul@chromium.org>,
	arm-linux <linux-arm-kernel@lists.infradead.org>,
	Icenowy Zheng <icenowy@aosc.io>
Subject: Re: [PATCH 4/4] arm64: DTS: allwinner: a64: enable ANX6345 bridge on Teres-I
Date: Fri, 17 May 2019 11:08:45 +0200	[thread overview]
Message-ID: <20190517090845.oujs33nplbaxcyun@flea> (raw)
In-Reply-To: <20190517101353.3e86d696@blackhole.lan>

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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@bootlin.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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