On Fri, Jan 15, 2016 at 9:46 AM, Mark Brown [off-list ref] wrote:

On Fri, Jan 15, 2016 at 09:49:50PM +0800, Caesar Wang wrote:

quoted

We need to claim the clock which is driving the codec so that when we
enable clock gating, we continue to clock the codec when needed.
I make this an optional clock since there might be some applications
where we don't need it but can still use the I2S block.

quoted

- As the perious discuss on https://patchwork.kernel.org/patch/5427131/,
  I think Mark likes do it in codec driver, I have to say I agree this
  patch in here since that's the i2s block output. I don't know if the
  Mark has changed his mind.

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.

Does that help clarify?