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Date:   Sun, 8 Nov 2020 15:34:09 +0000
From:   Jonathan Cameron <jic23@kernel.org>
To:     Artur Rojek <contact@artur-rojek.eu>
Cc:     Paul Cercueil <paul@crapouillou.net>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Peter Meerwald-Stadler <pmeerw@pmeerw.net>, od@zcrc.me,
        linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
Subject: Re: [PATCH] iio/adc: ingenic: Fix battery VREF for JZ4770 SoC
Message-ID: <20201108153409.723eeb8c@archlinux>
In-Reply-To: <1a319d53f1fd74b41056663421ef785e@artur-rojek.eu>
References: <20201104192843.67187-1-paul@crapouillou.net>
        <cb8b8ff426500db61c61b51413f3746c@artur-rojek.eu>
        <F3RAJQ.DZODDTV09KM21@crapouillou.net>
        <1a319d53f1fd74b41056663421ef785e@artur-rojek.eu>
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On Thu, 05 Nov 2020 01:27:51 +0100
Artur Rojek <contact@artur-rojek.eu> wrote:

> On 2020-11-05 01:09, Paul Cercueil wrote:
> > Hi Artur,
> >=20
> > Le mer. 4 nov. 2020 =C3=A0 23:29, Artur Rojek <contact@artur-rojek.eu> =
a=20
> > =C3=A9crit : =20
> >> Hi Paul,
> >>=20
> >> On 2020-11-04 20:28, Paul Cercueil wrote: =20
> >>> The reference voltage for the battery is clearly marked as 1.2V in=20
> >>> the
> >>> programming manual. With this fixed, the battery channel now returns
> >>> correct values.
> >>>=20
> >>> Fixes: a515d6488505 ("IIO: Ingenic JZ47xx: Add support for JZ4770 SoC=
=20
> >>> =7FADC.")
> >>> Cc: <stable@vger.kernel.org>
> >>> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> >>> ---
> >>>  drivers/iio/adc/ingenic-adc.c | 2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>=20
> >>> diff --git a/drivers/iio/adc/ingenic-adc.c=20
> >>> =7Fb/drivers/iio/adc/ingenic-adc.c
> >>> index ecaff6a9b716..19b95905a45c 100644
> >>> --- a/drivers/iio/adc/ingenic-adc.c
> >>> +++ b/drivers/iio/adc/ingenic-adc.c
> >>> @@ -71,7 +71,7 @@
> >>>  #define JZ4725B_ADC_BATTERY_HIGH_VREF_BITS	10
> >>>  #define JZ4740_ADC_BATTERY_HIGH_VREF		(7500 * 0.986)
> >>>  #define JZ4740_ADC_BATTERY_HIGH_VREF_BITS	12
> >>> -#define JZ4770_ADC_BATTERY_VREF			6600
> >>> +#define JZ4770_ADC_BATTERY_VREF			1200
> >>>  #define JZ4770_ADC_BATTERY_VREF_BITS		12
> >>>=20
> >>>  #define JZ_ADC_IRQ_AUX			BIT(0) =20
> >>=20
> >> I thought we set it to 6600 because GCW Zero was not showing correct=20
> >> battery values at 1200.
> >> But if you verified that 1200 works with JZ4770, then:
> >> Acked-by: Artur Rojek <contact@artur-rojek.eu> =20
> >=20
> > Yes, IIRC we were trying to figure out the range and settled with
> > [-3.3V,+3.3V] since it would give "plausible" values but which were
> > never quite right. The doc does say that the voltage is (hw_val /
> > 4096) * 1.2V, but also says that the ADC operated with 3.3V power
> > supply, I guess we got confused. We never considered the battery could
> > not be connected directly to the ADC's VBAT pin, so a 1.2V reference
> > didn't make sense at that time. I guess we need to learn about
> > electronics :) =20
> Yes we do :)
> >=20
> > It turns out the battery is connected to the VBAT pin with a 1 MOhm
> > resistor, and the VBAT pin is also pulled low with a 332 kOhm
> > resistor. So a fully charged battery with 4.2V reads as (4.2V *
> > 332000) / (1332000) =3D 1.05V, which totally fits in a [0V,+1.2V] range.
> >=20
> > With that same 4.2V battery I get a hardware value of about 3584, and
> > (3584 / 4096) * 1.2V =3D=3D 1.05V, which matches the value computed abo=
ve.
> > So the battery reading looks accurate this time. =20
> Excellent! Thanks for the detailed explanation.

Applied to the fixes-togreg branch of iio.git

Thanks,

Jonathan

>=20
> Cheers,
> Artur
> >=20
> > Cheers,
> > -Paul =20