[Gta04-owner] Reliable headset detection with raw values

Paul Kocialkowski contact at paulk.fr
Sat May 24 14:14:21 CEST 2014

> > This doesn't make much sense to me.
> > Rather than guessing I looked at the code, and the effect of setting 'raw'
> > is to bypass
> > 
> > 			buf[i] = (buf[i] * 3 * 1000 *
> > 				 twl4030_divider_ratios[i].denominator)
> > 				/ (2 * 1023 *
> > 				twl4030_divider_ratios[i].numerator);
> > 
> > where 'i' is 7, and twl4030_divider_ratios[7] is
> > 
> > 	{6, 10},	/* CHANNEL 7 */
> > 
> > So this becomes
> >    buf[i] * 30000 / 12276
> > 
> > so it rough multiplies the numbers be 2.5.  That shouldn't affect stability
> > at all.
> Yes, you're perfectly right, I didn't read twl4030_madc_read_channels
> completely and just assumed it was changing the range of values in a
> dynamic way (for instance, using calibration), but obviously, I was
> wrong. It really did seem like it was improving stability (for instance,
> I had values that drastically changed from one reboot to the other, like
> 800 to 400, without raw), but then it was late when I did this and I
> jumped to conclusions too fast, without learning about the details.
> I'll revert the change in the Replicant 4.2 tree and use thresholds
> based on the non-raw values.

Turns out I wasn't so crazy after all! My patch did introduce better
stability because the raw element of the request structure wasn't
initialized previously, which lead to randomly either raw or processed
values, hence the different ranges of values depending on the day, the
device, etc.

I've just pushed a patch to fix this in the Replicant 4.2 kernel[0]:
commit 2421efd8de974fee6a06e45ca31d4ed6f4805573
Author: Paul Kocialkowski <contact at paulk.fr>
Date:   Sat May 24 13:08:29 2014 +0200

    twl4030-madc: Request processed values in twl4030_get_madc_conversion
    Not setting the raw parameter in the request causes it to be randomly
    initialized to a value that might be different from zero or zero. This leads to
    values that are randomly either raw or processed, making it very difficult to
    make reliable use of the values.
    Signed-off-by: Paul Kocialkowski <contact at paulk.fr>

I suggest you include that patch in the other kernel trees. I've also
proposed a similar patch for mainline, so that this is not an issue for
anyone in the future!

By the way, the Replicant kernel is not using raw values anymore, and
I've adapted the thresholds[1]:

commit 47d0bd23e540b5fd8dcf4d722a8309d24ce9ee56
Author: Paul Kocialkowski <contact at paulk.fr>
Date:   Sat May 24 13:15:14 2014 +0200

    gta04-audio: Jack detection thresholds for processed values
    Signed-off-by: Paul Kocialkowski <contact at paulk.fr>


Paul Kocialkowski, Replicant developer

Replicant is a fully free Android distribution

Website:        http://www.replicant.us/
Wiki/Tracker:   http://redmine.replicant.us/
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