3.19 on Nokia n900: audio quality awful

[Jarkko Nikula]

On Wed, Jan 28, 2015 at 11:41:44PM +0100, Pavel Machek wrote:
> On Wed 2015-01-28 20:15:46, Jarkko Nikula wrote:
> > On 01/26/2015 03:20 PM, Peter Ujfalusi wrote:
> > > On 01/18/2015 02:01 PM, Pavel Machek wrote:
> > No need to go that far. N900 has been supported in mainline since 2.6.39
> > or so. Part A of AIC34 (which is basically dual AIC33 in a same package)
> > drives 2 V for the digital microphone bias and part B 2.5 V for the headset.
> 
> Let me try... Umm, no change here :-(
> 
> root at n900:/tmp# arecord delme
> Recording WAVE 'delme' : Unsigned 8 bit, Rate 8000 Hz, Mono
> ^CAborted by signal Interrupt...
> root at n900:/tmp# hexdump delme
> 0000000 4952 4646 987c 0000 4157 4556 6d66 2074
> 0000010 0010 0000 0001 0001 1f40 0000 1f40 0000
> 0000020 0001 0008 6164 6174 9858 0000 8080 8080
> 0000030 8080 8080 8080 8080 8080 8080 8080 8080
> *
> 0009880
> root at n900:/tmp# aplay delme
> Playing WAVE 'delme' : Unsigned 8 bit, Rate 8000 Hz, Mono
> root at n900:/tmp#
> 
> I did this:
> 
> I'm not sure which one is "main" microphone and which is headset, but
> I guess 2V should be "close enough" to 2.5V to produce something
> different from zeros..?
> 
Main or integrated is digital microphone which does AD conversion itself
and headset is analogue. If DMIC is without bias codec will sample plain
zeros from DMIC input but analogue input should always produce some random
LSB bits from codec's AD converter.

If codec produces zeros also from analogue input then I suppose codec
ADC is not powered up or similar. One way to hunt regression if
bisecting is not possible due reason or another is to dump and diff codec
registers from /sys/kernel/debug/regmap/ using both working commit and head.

> diff --git a/arch/arm/boot/dts/omap3-n900.dts b/arch/arm/boot/dts/omap3-n900.dts
> index 48b0987..f18a5b0 100644
> --- a/arch/arm/boot/dts/omap3-n900.dts
> +++ b/arch/arm/boot/dts/omap3-n900.dts
> @@ -491,6 +491,8 @@
>  		DRVDD-supply = <&vmmc2>;
>  		IOVDD-supply = <&vio>;
>  		DVDD-supply = <&vio>;
> +
> +		ai3x-micbias-vg = <1>;
>  	};
Looks ok for digital mic.

>  
>  	tlv320aic3x_aux: tlv320aic3x at 19 {
> @@ -502,6 +504,8 @@
>  		DRVDD-supply = <&vmmc2>;
>  		IOVDD-supply = <&vio>;
>  		DVDD-supply = <&vio>;
> +
> +		ai3x-micbias-vg = <1>;
>  	};
This should be 2, i.e. 2.5 V according to
Documentation/devicetree/bindings/sound/tlv320aic3x.txt. I think 2 V is
too low for some headset mics and that was the reason for 2.5 V.

-- 
Jarkko