[alsa-devel] ASoC: wm9712: Microphone doesn't work, "Capture Volume" inverted

Mark Brown broonie at opensource.wolfsonmicro.com
Tue May 1 19:12:07 CEST 2012

On Tue, May 01, 2012 at 01:44:58AM +0200, Hans J. Koch wrote:
> On Mon, Apr 30, 2012 at 10:43:33PM +0100, Mark Brown wrote:

> > I'm not entirely sure you've looked at the code here...

> Oh yes, sorry. I got distracted by your mentioning of the suppressed writes.
> Actually, we have suppressed reads. ac97_read() does a "return cache[reg];"
> for most registers, assuming the hardware register cannot change after a
> ac97_write(). That might or might not be true, to me it looks dangerous.

The driver knows exactly which registers are volatile and takes
advantage of this - this is entirely idiomatic for devices like this and
not really that hard to get right.
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