How to implement capture_switch control?

How to implement capture_switch control?

[Adam Jiang]

Hello list,

I have a device with wm8903 codec. To support mute/unmute capture
signal, I was trying to enable/disable PGA on this codec from user
space application like

snd_ctl_elem_value_set_boolean("Left Input PGA Switch", 0, 0)

That means the mute/unmute function became platform dependent. I got
the idea to support mute/unmute function with enabling/disabling
capture switch. However, the function

snd_mixer_selem_has_capture_switch()

alwasy return false. I guess something is missing in my driver. Could
you please give some bright how could I use capture switch to
mute/unmute a channel. How could I implement capture_switch control
properly? Thank you!

/Adam

Re: How to implement capture_switch control?

[Mark Brown]

On Mon, Jun 20, 2011 at 04:15:38PM +0900, Adam Jiang wrote:

> I have a device with wm8903 codec. To support mute/unmute capture
> signal, I was trying to enable/disable PGA on this codec from user
> space application like

If the hardware does not physically support mute then this should be
emulated in software.  In the case of the WM8903 the device does not
have a specific capture mute control, though extremely low gains are
supported for the Capture Volume control which function as a mute so 
you could also set minimum Capture Volume.

> alwasy return false. I guess something is missing in my driver. Could
> you please give some bright how could I use capture switch to
> mute/unmute a channel. How could I implement capture_switch control
> properly? Thank you!

Not all hardware supports all possible features.  Either configure a
software volume control, the softvol plugin for ALSA should be able to
do this, or adjust your application to handle this in the application
layer.

http://alsa.opensrc.org/How_to_use_softvol_to_control_the_master_volume

has some information on using softvol.

Re: How to implement capture_switch control?

[Adam Jiang]

2011/6/21 Mark Brown <broonie@opensource.wolfsonmicro.com>:
> On Mon, Jun 20, 2011 at 04:15:38PM +0900, Adam Jiang wrote:
>
>> I have a device with wm8903 codec. To support mute/unmute capture
>> signal, I was trying to enable/disable PGA on this codec from user
>> space application like
>
> If the hardware does not physically support mute then this should be
> emulated in software.  In the case of the WM8903 the device does not
> have a specific capture mute control, though extremely low gains are
> supported for the Capture Volume control which function as a mute so
> you could also set minimum Capture Volume.

I got the idea about software emulation for mute. Would you please
point me to an example about device/driver where hardware capture
switch is supported?

>
>> alwasy return false. I guess something is missing in my driver. Could
>> you please give some bright how could I use capture switch to
>> mute/unmute a channel. How could I implement capture_switch control
>> properly? Thank you!
>
> Not all hardware supports all possible features.  Either configure a
> software volume control, the softvol plugin for ALSA should be able to
> do this, or adjust your application to handle this in the application
> layer.
>
> http://alsa.opensrc.org/How_to_use_softvol_to_control_the_master_volume
>
> has some information on using softvol.
>

I have solved the problem by enabling/disabling PGA for analog input
paths. For digital mic on wm8903, this function could be implemented
by turning volume to lowest level for mute, and restore volume level
for unmute. Thank you!

Re: How to implement capture_switch control?

[Mark Brown]

On Wed, Jun 22, 2011 at 04:56:26PM +0900, Adam Jiang wrote:
> 2011/6/21 Mark Brown <broonie@opensource.wolfsonmicro.com>:
> > On Mon, Jun 20, 2011 at 04:15:38PM +0900, Adam Jiang wrote:

> > If the hardware does not physically support mute then this should be
> > emulated in software. ?In the case of the WM8903 the device does not
> > have a specific capture mute control, though extremely low gains are
> > supported for the Capture Volume control which function as a mute so
> > you could also set minimum Capture Volume.

> I got the idea about software emulation for mute. Would you please
> point me to an example about device/driver where hardware capture
> switch is supported?

grep "Capture Switch" sound/soc/codecs/*.c

Re: How to implement capture_switch control?

[Adam Jiang]

2011/6/22 Mark Brown <broonie@opensource.wolfsonmicro.com>:
> On Wed, Jun 22, 2011 at 04:56:26PM +0900, Adam Jiang wrote:
>> 2011/6/21 Mark Brown <broonie@opensource.wolfsonmicro.com>:
>> > On Mon, Jun 20, 2011 at 04:15:38PM +0900, Adam Jiang wrote:
>
>> > If the hardware does not physically support mute then this should be
>> > emulated in software. ?In the case of the WM8903 the device does not
>> > have a specific capture mute control, though extremely low gains are
>> > supported for the Capture Volume control which function as a mute so
>> > you could also set minimum Capture Volume.
>
>> I got the idea about software emulation for mute. Would you please
>> point me to an example about device/driver where hardware capture
>> switch is supported?
>
> grep "Capture Switch" sound/soc/codecs/*.c
>

I got wm8904 as an example. In the driver of wm8904, there is a
control defined as

SOC_DOUBLE_R("Capture Switch", WM8904_ANALOGUE_LEFT_INPUT_0,
            WM8904_ANALOGUE_RIGHT_INPUT_0, 7, 1, 0),

And, there is also its peer in wm8903 defined as

SOC_SINGLE("Left Input PGA Switch", WM8903_ANALOGUE_LEFT_INPUT_0,
          7, 1, 1),

I checked their datasheet and I found there is no difference between
the registers of ANALOGUE_LEFT_INPUT_0. Both of them have one bit for
mute/unmute analog input path. Comparing SOC_SINGLE and SOC_DOUBLE
macro, one snd_soc_control structure is missing in former. What is
exactly the difference between the two definitions. Is there any docs
to describe how could I use these macros in soc.h?