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

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Date:	Wed, 3 Dec 2014 15:03:40 -0800
From:	Sonny Rao <sonnyrao@...omium.org>
To:	Mark Brown <broonie@...nel.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 3, 2014 at 12:03 PM, Mark Brown <broonie@...nel.org> wrote:
> 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...

Yeah, sorry.

> 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.

Ok, then I think what we will do is abandon this patch and I will send
something that adds this functionality to the particular codec that
I'm interested in -- max98090.

I'm a little tied up at the moment so I'm not going to send that for a
little while, but will come eventually.

Thanks for the advice!
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