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

Mark Brown broonie at opensource.wolfsonmicro.com
Mon Apr 30 23:43:33 CEST 2012

On Mon, Apr 30, 2012 at 09:40:55PM +0200, Hans J. Koch wrote:
> On Thu, Apr 26, 2012 at 10:37:45PM +0100, Mark Brown wrote:
> > On Thu, Apr 26, 2012 at 11:11:33PM +0200, Christoph Fritz wrote:

> > > ac97_write() doesn't get called when I try to change "Item: Differential Source".

> > Oh, right - you're not actually seeing any attempt to write.  There
> > won't be anything on the bus, then.  Still, why are you identifying the
> > shift there?  The write will be suppresed if the register contents don't
> > change which looks like what you're seeing here - though I can't see
> [...]

> I overlooked that one. What kind of horror show is that? It's definetly wrong
> to make any assumptions about hardware register contents. A low-level write
> function always has to write the given value to the given register. Everything
> else, like suppressing a write because you _think_ a register hasn't changed,
> will sooner or later lead to hard-to-find errors.

> Any performance optimizations have to take place on the highest possible level.

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