linux-kernel - Re: [PATCH v2 2/2] ASoC: rockchip: i2s: add support for grabbing output clock to codec

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Message-ID: <20141203200307.GM7712@sirena.org.uk>
Date:	Wed, 3 Dec 2014 20:03:07 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Sonny Rao <sonnyrao@...omium.org>
Cc:	Jianqun Xu <jay.xu@...k-chips.com>,
	Liam Girdwood <lgirdwood@...il.com>, perex@...ex.cz,
	tiwai@...e.de, Heiko Stübner <heiko@...ech.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	alsa-devel@...a-project.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v2 2/2] ASoC: rockchip: i2s: add support for grabbing
 output clock to codec

On Wed, Dec 03, 2014 at 11:38:13AM -0800, Sonny Rao wrote:
> On Wed, Dec 3, 2014 at 11:20 AM, Mark Brown <broonie@...nel.org> wrote:

> > I would expect that the clock for the CODEC should be managed by the
> > CODEC if at all possible - that seems more logical than having the CPU
> > I2S controller request and manage it if it's a separate clock.  Why add
> > this to the CPU side driver?

> This output clock has a mux and can either be a fixed 12Mhz output or
> can be derived from the same fractional divider which drives the i2s
> block.   I thought it was simpler to keep them all the same, but need
> to put ownership in the i2s in anticipation of the i2s driver setting
> it's own clock rate.

> If you think this is an implementation detail and this output clock
> should just be owned by the codec driver, even though I'm guessing it
> will just have to be the same as i2s, then I think we can drop this
> and make sure simple card (or whatever other codec driver) claims this
> clock.

simple-card obviously isn't a CODEC driver...  For generality I think
the clock does need to be exposed to the CODEC driver, otherwise this
will work differently to how other systems are working and we can't
substitute in a different clock on the CODEC side so easily if it
doesn't happen to use the output from the I2S block.

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