[alsa-devel] mic bias for tlv320aic3x?

Peter Meerwald pmeerw at pmeerw.net
Wed Nov 28 10:28:53 CET 2012


> > I'd like to enable 2V mic bias on the tlv320aic3x (which offers 2V, 2.5V, 
> > AVDD, off) -- I'd have expected some control in alsamixer to so, but there 
> > is none
> > what is the proper way to implement mic bias selection?
> As platform data or possibly via an API offered to the machine driver,
> we've yet to see any use case where it's something that should be varied
> directly from the application layer.

I can see the platform data way

I'd be happy with an API to control from the machine driver -- is 
snd_soc_dapm_enable_pin() to be used for this + some SND_SOC_DAPM_MIC? 

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

is there a good reference driver?

per default, Mic Bias is off
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

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

thanks, regards, p.


Peter Meerwald
+43-664-2444418 (mobile)

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