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

From: Jianqun Xu
Date: Sun Jan 24 2016 - 20:16:30 EST

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@xxxxxxxxxx> 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

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.