[Letux-kernel] Kobolino: rc5t619 adc

[Andreas Kemnade]

On Sat, 21 Dec 2019 16:25:50 +0100
"H. Nikolaus Schaller" <hns at goldelico.com> wrote:

> > Am 21.12.2019 um 15:15 schrieb Andreas Kemnade <andreas at kemnade.info>:
> > 
> > On Sat, 21 Dec 2019 13:31:08 +0100
> > "H. Nikolaus Schaller" <hns at goldelico.com> wrote:
> >   
> >>> Am 21.12.2019 um 09:32 schrieb Andreas Kemnade <andreas at kemnade.info>:
> >>> 
> >>> On Sat, 21 Dec 2019 09:05:49 +0100
> >>> "H. Nikolaus Schaller" <hns at goldelico.com> wrote:
> >>>   
> >>>> Hi,
> >>>>   
> >>>>> Am 20.12.2019 um 21:15 schrieb Andreas Kemnade <andreas at kemnade.info>:
> >>>>> 
> >>>>> Hi,
> >>>>> 
> >>>>> in the branch
> >>>>> letux/kobolino/rtc-v5      
> >>>> 
> >>>> Fine. I have prepared to merge it into letux-5.5-rc3.
> >>>>   
> >>> don't forget the additional CONFIG    
> >> 
> >> Ok, is working!
> >> 
> >> Only the scaling seems to be wrong. AFAIR, the in*_input are scaled
> >> as mV and not µV as other interfaces. I think there was some document
> >> in Documentation/ but I couldn't locate it quickly.
> >>   
> > well, there is no *1000 in the generic_adc_battery driver,
> > so if gab is right, iio must deliver uV. Or the other way round,
> > if iio has to deliver mV, then gab is wrong.
> > Or am I missing something?  
> 
> Well, I would more assume that gab is wrong...
> 
> If I read twl4030 or Palmas iio channels I obviously get mV:
> 
> root at letux:~# ./findiio palmas-gpadc
> /sys/bus/iio/devices/iio:device2
> root at letux:~# cat /sys/bus/iio/devices/iio:device2/in_*_input
> 710
> 4602
> 0
> 2840
> 0
> 783
> 0
> 0
> 3960
> 4162
> 2476
> 5001
> root at letux:~#
> 
> Or these are badly defined?
> 
> Well, /sys/class/power_supply gives µV and µA but they do not need to be the same definitions as iio.
> 
> And here is a hint:
> 
> https://wiki.analog.com/resources/tools-software/linux-drivers/iio-adc/ad7887
> 
> 	scale to be applied to in0_raw in order to obtain the measured voltage in millivolts.
> 	This specifies any shell prompt running on the target
> 	root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat in_voltage_scale
> 
> So this means the scale must scale the _raw to mV. And _input is just the value after applying scale and offset. This is then also mV.
> 
> Here is another doc:
> 
> https://wiki.st.com/stm32mpu/index.php/How_to_use_the_IIO_user_space_interface#How_to_do_a_simple_conversion_using_the_sysfs_interface
> 
> It seems as if this is NOT well documented and taken for granted by everyone...
> 	
so probably better to use mV then. I will add a patch.

> > But more interesting is the scaling of in_current.  
> 
> Well, for me correct voltage readings are initially more important
> since user-space (/root/charger script) may rely on a certain unit
> of values.
> 
well interesting != important. µV vs. mV is just a decision.

> But scaling in_current is also important.
> 
> Most likely it is a shunt resistor measuring the
> current from the USB power supply to the battery charger.
> And contrary to the twl4030 not the current going into
> or coming from battery. I.e. the twl4030 can measure
> positive and negative current. AFAIR, there are also
> two separate ADC wires and channels reserved.
> 
The rc5t619 uses two shunts, one attached to the adc and
charger control and one attached to the fuel gauge and charger
control.

> Without schematics and knowing the exact resistor value
> it is very difficult to calibrate it.
> 
resistor is 20mOhm, as specified by the data sheet. I found two of those
near the pmic. 

Regards,
Andreas