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

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Date:	Tue, 26 Jan 2016 10:52:25 +0100
From:	Heiko Stübner <heiko@...ech.de>
To:	Jianqun Xu <jay.xu@...k-chips.com>
Cc:	Mark Brown <broonie@...nel.org>, Sonny Rao <sonnyrao@...omium.org>,
	Caesar Wang <wxt@...k-chips.com>,
	"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 Jay,

Am Montag, 25. Januar 2016, 09:15:31 schrieb Jianqun Xu:
> 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 ?

The mclk-input is part of the codec I'd think. So you'd want the clocks-
property in the i2c entry describing the codec itself and implement the clk 
operations in the codec driver as well.

See codec-drivers for da7213, da7218,max98090 and many more for reference.


Heiko



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