[alsa-devel] [PATCH 1/3] ASoC: cs4270: fix Master Capture Switch polarity

Takashi Iwai tiwai at suse.de
Sun Apr 26 13:08:22 CEST 2009

At Sun, 26 Apr 2009 10:49:17 +0100,
Mark Brown wrote:
> On Fri, Apr 24, 2009 at 10:45:29AM -0500, Timur Tabi wrote:
> > Daniel Mack wrote:
> > > The control modifies the MUTE register, hence the polarity must be
> > > inverted.
> >                             L    R
> >                             CAPTUR
> > 
> >                           < Master >
> > What exactly does this mean?  Which one is supposed to mean "muted"?
> Capture is enabled in the picture above; often when the alsamixer UI is
> confusing amixer is a bit clearer about what's going on.

The "mute" is only for "* Playback Switch" mixer controls.  In this case,
if you have "Master Playback Switch", it's handled as the mute switch
in the mixer interface.  If you don't have such a control element,
there is no "mute" for "Master" mixer element.

OTOH, "* Capture Switch" is handled as "capture" switch, which is
indicated as "CAPTURE" (and "L" & "R") in the above.  Also, if the
driver supports rather "Capture Source" enum instead of "XXX
Capture Switch", its list items are converted to multiple exclusive 
"capture" switches.

> > And how come even though this switch is a SOC_DOUBLE, I cannot control
> > the left and right channel independently with the < and > keys, and the
> > "M" key doesn't toggle it either.
> This is a property of capture controls.  I'm not entirely sure why,
> CCing in Takashi who should be able to offer more knowledgable comment.

The keys you mentioned above are all for playback mute controls, thus
irrelevant with the capture switch.  User space key to toggle the
capture switch.


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