[alsa-devel] [PATCH 2/8] ASoC: Add support for virtual switch controls

[Mark Brown]

On Thu, Jan 10, 2013 at 05:06:11PM +0100, Lars-Peter Clausen wrote:

> More specific this will be used by the ADAU1361 driver where the hardware has
> a mute control for each of the DAC output paths, but we have to make sure that
> the path is muted whenever the DAC is disabled. So the mute switches needs
> to be controlled by DAPM so it can disable them before disabling the DAC. On the
> other hand we still want to be to mute individual paths. This will be
> accomplished by using virtual switch controls.

This doesn't sound like it does quite what you want - it means you don't
actually end up with a mute control, only a power control (which is also
going to affect everything else in the path).  I'd expect to see
something like this implemented by having a control that has a specified
value forced in the register while the control is enabled (kind of the
opposite of a supply).  This is a fairly common need for older parts
though it's unusual to see it on a new device.
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