[PATCH v2 2/6] ASoC: xilinx: xlnx_formatter_pcm: Handle sysclk setting

[Mark Brown]

On Mon, Jan 10, 2022 at 09:24:38PM +0000, Robert Hancock wrote:
> On Mon, 2022-01-10 at 20:31 +0000, Mark Brown wrote:

> > If the device is using mclk-fs then either there's a fixed sample rate
> > (in which case simple-card probably ought to force it without the driver
> > worrying) or the sysclk will vary in which case simple-card should be
> > setting the sysclk to 0 when the card goes idle to clear any
> > constraints (which as you say later it does).

> It sounds like to fix that, simple-card needs to keep track of whether the DAI
> has a fixed clock rate or not. If it does, then it shouldn't be zeroing out the
> sysclk when closing the device as that's wiping out information that needs to
> be persistent. I guess if the frequency was read from a system-clock-frequency
> property then we know it is fixed. There are other cases where it could be a
> fixed rate, such as if the clock is connected to a fixed-clock. Maybe we need
> an explicit DT flag "system-clock-fixed" or something for those cases?

If the clock is fixed in the clock API we should arrange to be able to
enumerate that from the clock API - we shouldn't be requiring redundant
properties for something like that.

> Then at least in the case where mclk-fs is set and one or more of the DAIs have
> a fixed rate, simple-card can add a constraint to restrict the sample rate to
> the fixed clock divided by mclk-fs?

Yes, however we figure out that sysclk is fixed.
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