linux-kernel - Re: [PATCH v9 1/4] drm/i2c: tda998x: Add DT support for audio

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Message-ID: <20150114125056.GU4160@sirena.org.uk>
Date:	Wed, 14 Jan 2015 12:50:56 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Philipp Zabel <p.zabel@...gutronix.de>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Jyri Sarha <jsarha@...com>,
	Jean-Francois Moine <moinejf@...e.fr>,
	Andrew Jackson <Andrew.Jackson@....com>,
	Dave Airlie <airlied@...il.com>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 1/4] drm/i2c: tda998x: Add DT support for audio

On Wed, Jan 14, 2015 at 11:46:58AM +0100, Philipp Zabel wrote:

> So the question is mostly whether four I2S data pins with a single
> shared WS/SCK input should be called "four I2S ports with shared clocks"
> or "one I2S port with up to four data lanes". I'd lean towards the
> latter.

Yes, this is what we're doing for the Samsung CPU side controllers which
implement this natively and seems to make sense here too - the different
channels can't really work as separate interfaces in any practical way.

> How audio2_i2s is forced to synchronize its clock output to audio1_i2s
> is a problem their bindings will have to handle.

Trying to hook up a controller that doesn't natively support this format
to a device that uses it is definitely tricky, as well as describing the
physical hookup we also need to worry about how things look to userspace
- it's ideally going to want a single multi-channel audio stream.

I think from a binding point of view we need a way to say "this endpoint
on the link is constructed from these DAIs on the device side" and say
if this is TDM or multi-data, and what's driving the clocks.

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