Re: [PATCH RFC] arm64: dts: allwinner: a64: teres-i: Enable audio

From: Maxime Ripard <maxime.ripard@bootlin.com>
To: Harald Geyer <harald@ccbib.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	devicetree@vger.kernel.org, info@olimex.com,
	Mark Brown <broonie@kernel.org>, Chen-Yu Tsai <wens@csie.org>,
	Rob Herring <robh+dt@kernel.org>, Torsten Duwe <duwe@lst.de>,
	ibu@radempa.de, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH RFC] arm64: dts: allwinner: a64: teres-i: Enable audio
Date: Mon, 18 Feb 2019 11:24:42 +0100	[thread overview]
Message-ID: <20190218102442.l3br2h3oqfe2atdv@flea> (raw)
In-Reply-To: <E1gv6rh-0000Km-U8@stardust.g4.wien.funkfeuer.at>

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On Sat, Feb 16, 2019 at 09:47:13PM +0100, Harald Geyer wrote:
> Hi Torsten!
> 
> Torsten Duwe writes:
> 
> > > > > > > But we need a way to control the mux from userspace and aside from
> > > > > > > unbinding the ideas proposed thus far are:
> > > > > > >
> > > > > > > a) control the gpio directly
> > > > > > > b) control the gpio via leds-gpio
> > > > > > > 
> > > > > > > (a) was dismissed because we can't set a default from DT
> > > > > > > (b) was dismissed because some rogue app might try to blink it
> > 
> > Hey, this is a debugging hack. If some rogue app tries to blink it, so be it.
> > 
> > > I suspect some distributions will pick up the patch I posted anyway, if
> > > it doesn't get merged mainline. (This is how I forgot missing backlight
> > > support - it just worked for too many people ...) If we ship
> > > sun50i-a64-teres-i.dts with the proper nodes (but disabled), their
> > > patches will be much easier to maintain as the official DT evolves.
> > 
> > As I wrote (held by the list admin), I consider the whole console mux
> > GPIO an U-Boot hack, and would put it into sun50i-a64-teres-i-u-boot.dtsi.
> > (As a LED, see above :-)
> 
> The thing is, one of the quite strict rules in kernel development is:
> Never break userspace. That means: If we provide a way to userspace to
> do something (ie switch between debug and audio), we are expected to
> keep it around forever. So since there is a decent chance that someday
> somebody might write a driver that handles this situation properly, we
> don't want chain ourselves to some dirty hack.
> 
> (I'm not totally against writing such a driver myself, if there are
> enough use cases. However, I think that TERES alone is not enough.)
> 
> > Would you care to submit a patch version without that GPIO handled?
> > I think it's very useful and has the potential to be agreed upon.
> 
> That would enable audio from the internal speakers but select debug
> output on the HP jack by default. I would be okay with that, despite
> still thinking that audio on the head phones should be the default.
> 
> Maxime and Wens are the maintainers, so it's their call in the end.

At this point, I'm not really convinced by the solution in that patch,
but I don't have really good ideas either. I think it would be good to
discuss this with Mark and Linus Walleij, they will probably have way
better solutions than what I can come up with.

Maxime

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

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