linux-kernel - Re: [PATCH] iio/adc: ingenic: Fix battery VREF for JZ4770 SoC

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1a319d53f1fd74b41056663421ef785e@artur-rojek.eu>
Date:   Thu, 05 Nov 2020 01:27:51 +0100
From:   Artur Rojek <contact@...ur-rojek.eu>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>, od@...c.me,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] iio/adc: ingenic: Fix battery VREF for JZ4770 SoC

On 2020-11-05 01:09, Paul Cercueil wrote:
> Hi Artur,
> 
> Le mer. 4 nov. 2020 à 23:29, Artur Rojek <contact@...ur-rojek.eu> a 
> écrit :
>> Hi Paul,
>> 
>> On 2020-11-04 20:28, Paul Cercueil wrote:
>>> The reference voltage for the battery is clearly marked as 1.2V in 
>>> the
>>> programming manual. With this fixed, the battery channel now returns
>>> correct values.
>>> 
>>> Fixes: a515d6488505 ("IIO: Ingenic JZ47xx: Add support for JZ4770 SoC 
>>> ADC.")
>>> Cc: <stable@...r.kernel.org>
>>> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
>>> ---
>>>  drivers/iio/adc/ingenic-adc.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>> 
>>> diff --git a/drivers/iio/adc/ingenic-adc.c 
>>> b/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
>>> 
>>>  #define JZ_ADC_IRQ_AUX			BIT(0)
>> 
>> I thought we set it to 6600 because GCW Zero was not showing correct 
>> battery values at 1200.
>> But if you verified that 1200 works with JZ4770, then:
>> Acked-by: Artur Rojek <contact@...ur-rojek.eu>
> 
> 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 :)
Yes we do :)
> 
> 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) = 1.05V, which totally fits in a [0V,+1.2V] range.
> 
> With that same 4.2V battery I get a hardware value of about 3584, and
> (3584 / 4096) * 1.2V == 1.05V, which matches the value computed above.
> So the battery reading looks accurate this time.
Excellent! Thanks for the detailed explanation.

Cheers,
Artur
> 
> Cheers,
> -Paul