[alsa-devel] [PATCH] ASoC: da732x: Mark DC offset control registers volatile

Mark Brown broonie at kernel.org
Tue Feb 25 02:21:38 CET 2014

On Mon, Feb 24, 2014 at 01:57:53PM +0000, Opensource [Adam Thomson] wrote:

> anyway. I'd be tempted to keep it simple and just make those registers volatile,
> then you know it will work as expected, at least for the time being until a

That breaks suspend and resume without further work - for suspend and
resume we generally rely on restoring the register cache to restore the
current settings but if a register is volatile it won't be cached so
will go back to the hardware defaults after suspend.  The ability to
avoid I2C traffic is partly just a nice side effect (though it was
needed on devices that don't have readback), the main thing these days
is that controls get efficient suspend and resume handling for free.

Refactoring the offset correction to happen once on startup would solve
the issue since the cache could just be bypassed, though you are likely
to find that there is some run to run variation for the callibration due
to effects like thermal variation and simple measurement errors.  Still,
the effects are typically very small.
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