[alsa-devel] [PATCH 10/10] ASoC: dapm: Implement mixer input auto-disable

Lars-Peter Clausen lars at metafoo.de
Thu Aug 1 21:24:11 CEST 2013

On 08/01/2013 12:48 PM, Mark Brown wrote:
> On Mon, Jul 29, 2013 at 05:14:04PM +0200, Lars-Peter Clausen wrote:
>> -	ucontrol->value.integer.value[0] =
>> -		(snd_soc_read(codec, reg) >> shift) & mask;
>> +	mutex_lock_nested(&card->dapm_mutex, SND_SOC_DAPM_CLASS_RUNTIME);
>> +	if (dapm_kcontrol_is_powered(kcontrol))
>> +		val = (snd_soc_read(codec, reg) >> shift) & mask;
>> +	else
>> +		val = dapm_kcontrol_get_value(kcontrol);
>> +	mutex_unlock(&card->dapm_mutex);
>> +
> My first thought looking at this is that I would expect this to be
> encapsulated in kcntrol_get_value(), though at the minute it's actually
> only returning the virtual value which makes sense for the existing use.
> Equally well I'd expect the value to always be a functioning cache of
> the real value so I think what I'm really saying here is that I don't
> think we should really be checking if the control is powered at all.  We
> do need the I/O path but the power isn't the reason for it, the fact
> that we have the value stashed locally is.

There might be some corner cases where the driver directly modifies the 
register value outside of put_volsw() which would break. But otherwise I agree.

> Another thing that's bothering me here is that this only works for mono
> controls but many of the uses are stereo mutes and/or volumes.  We'd
> need to add back the support for those.

But that's a general limitation for DAPM controls. Right now 
snd_soc_dapm_put_volsw() only supports mono controls. If we have a left and a 
right mixer we usually have one mono control for each side. But I of course it 
would be nice to have support for stereo controls here. I guess with the shared 
control infrastructure we actually have most of what we need in place. The only 
thing missing is a way to express which channel of the control controls which 
path. E.g. an extra field per path or per mixer widget selecting the index.

- Lars

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