Re: [PATCH v5 1/2] ASoC: fsl: Add S/PDIF CPU DAI driver

On Friday 16 of August 2013 10:56:32 Sascha Hauer wrote:

On Fri, Aug 16, 2013 at 04:01:25PM +0800, Nicolin Chen wrote:

quoted

Hi Sascha,

   Thank you for the detailed comments.

On Fri, Aug 16, 2013 at 09:08:18AM +0200, Sascha Hauer wrote:

quoted

Which of them the driver should use is configuration and thus
normally
should *not* be described in the devicetree. However, there may be
no
good way for the driver to know which clock to use in which case.
There
may be additional board requirements which are unknown to the
driver. So in this case it might be valid to put the information
which clock to use into the devicetree. But be aware that from the
moment you put this information into the devicetree the driver is
no longer free to chose the best clock, even if in future we find a
good way to automatically guess the best clock. Do you have some
insights in which case I would use which input clock? Is this only
about which clock has the best suitable input frequency or is this
also about synchronization of the audio signal with some other
unit?

I understand. What I'm thinking now is to let the driver find the best
clock source for tx clock and a correspond divisor like this:

"tx<0-8>"	Optional	Tx clock source for spdif playback.

				If absent, will use core clock.
				The index from 0 to 8 is identical
				to the clock source list described
				in TxClk_Source bit of register STC.
				Multiple clock source are allowed
				for this tx clock source. The driver
				will select one source from them for
				each supported sample rate according
				to the clock rates of these provided
				clock sources.

You mean tx<0-7>.

Also I would make this option required. Use a dummy clock for mux inputs
that are grounded for a specific SoC.

Why do you need a dummy clock?

The driver can simply try to grab all the possible clocks and discard 
those that failed, so you can just keep those grounded clocks unspecified.

Best regards,
Tomasz