[alsa-devel] mic bias for tlv320aic3x?

Mark Brown broonie at opensource.wolfsonmicro.com
Wed Nov 28 10:35:34 CET 2012

On Wed, Nov 28, 2012 at 10:28:53AM +0100, Peter Meerwald wrote:

> I am missing the overall strategy how this is supposed to work

> is there a good reference driver?

Currently nobody is implementing this dynamically, it's always
configured via platform data.

> per default, Mic Bias is off

Well, of course...  it's just a normal thing in DAPM.

> there already are some mic bias definitions in tlv320aic3x:

> 	/* Mic Bias */
> 	SND_SOC_DAPM_REG(snd_soc_dapm_micbias, "Mic Bias 2V",
> 			 MICBIAS_CTRL, 6, 3, 1, 0),
> 	SND_SOC_DAPM_REG(snd_soc_dapm_micbias, "Mic Bias 2.5V",
> 			 MICBIAS_CTRL, 6, 3, 2, 0),
> 	SND_SOC_DAPM_REG(snd_soc_dapm_micbias, "Mic Bias AVDD",
> 			 MICBIAS_CTRL, 6, 3, 3, 0),

> however, those are not referenced anywhere and it is not clear how to 
> access those from the machine driver

I'm not clear what the above is intended to do but I think you're
supposed to pick the MICBIAS you want to use in your board when you're
hooking it up.

> as for the use case: user wants to connect either a microphone or line-in 
> to a connector, hence mic bias selection is necessary -- this doesn't 
> sound so unusual

Normally this sort of thing would be done automatically by the kernel
detecting what's plugged in, not manually by an application.
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