linux-kernel - Re: [PATCH v3 3/9] ASoC: rockchip: i2s: add support for grabbing output clock to codec

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Date:	Mon, 25 Jan 2016 09:15:31 +0800
From:	Jianqun Xu <jay.xu@...k-chips.com>
To:	Mark Brown <broonie@...nel.org>, Sonny Rao <sonnyrao@...omium.org>
Cc:	Caesar Wang <wxt@...k-chips.com>, Heiko Stuebner <heiko@...ech.de>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	leozwang@...gle.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Kees Cook <keescook@...gle.com>
Subject: Re: [PATCH v3 3/9] ASoC: rockchip: i2s: add support for grabbing
 output clock to codec

Hi Mark

在 23/01/2016 01:18, Mark Brown 写道:
> On Fri, Jan 15, 2016 at 01:48:04PM -0800, Sonny Rao wrote:
>> On Fri, Jan 15, 2016 at 9:46 AM, Mark Brown <broonie@...nel.org> wrote:
>
>>> If the I2S block is providing a clock to the CODEC then that's what the
>>> software should do so that the CODEC can gate and ungate the clock as
>>> required.  This patch has the I2S block using a clock, not providing
>>> one.
>
>>  From my read of the clock diagram for RK3288  there is a single clock
>> signal (labeled "clk_i2s0") that comes out of a fractional divider,
>> and it is split such that one path gets sent to the I2S block and the
>> second path is sent to a mux after which that signal is sent to an
>> external pin that goes to the codec.
>
>> There are separate clock gates for the two paths: one for the I2S
>> block and one after that mux before the external pin.
>
>> I'm not sure if it's being modeled that way in the Linux code or not,
>> but at least physically I don't think this clock signal actually goes
>> through the I2S block before being sent to the codec.
>
> That's not really the issue here, the issue is that it's not the I2S
> controller that is consuming the clock so it should not be the I2S
> controller driver that ensures that the clock is enabled.  The driver
> that manages the clock should be the one that uses it, like I say this
> means you should add the code to enable the clock to the CODEC driver if
> the CODEC driver needs the clock enabled.
>
Agree, now we almost use the simple-card for the CODEC driver, so I 
think we should enable the mclk(i2s-outclk) in the simple-card driver, 
is it ?

I found a subnode property from simple-card document:
- mclk-fs                               : Multiplication factor between 
stream
                                           rate and codec mclk, applied 
only for
                                           the dai-link.
But the property responsible to the factor, not care if the mclk source 
clock is enabled or not. So does the simple-card driver can add support 
to enable/disable mclk ?

>> Does that help clarify?
>
> The problem here isn't a lack of clarity in the situation.
>