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

From: Vasily Khoruzhick <anarsoul@gmail.com>
To: Torsten Duwe <duwe@lst.de>
Cc: Mark Rutland <mark.rutland@arm.com>,
	devicetree <devicetree@vger.kernel.org>,
	Andrzej Hajda <a.hajda@samsung.com>,
	David Airlie <airlied@linux.ie>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Maxime Ripard <maxime.ripard@bootlin.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: Thu, 16 May 2019 09:06:41 -0700	[thread overview]
Message-ID: <CA+E=qVe5NkAvHXPvVc7iTbZn5sKeoRm0166zPW_s83c2gk7B+g@mail.gmail.com> (raw)
In-Reply-To: <20190516154820.GA10431@lst.de>

On Thu, May 16, 2019 at 8:48 AM Torsten Duwe <duwe@lst.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@lst.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
>

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