Re: ina226 as IIO device instead of HWMON

[Guenter Roeck <linux@roeck-us.net>]

On Fri, Aug 09, 2019 at 03:42:00PM +0200, Michal Simek wrote:
> On 09. 08. 19 15:02, Guenter Roeck wrote:
> > Hi Michal,
> > 
> > On 8/9/19 3:37 AM, Michal Simek wrote:
> >> Hi,
> >>
> >> we are dealing with one issue with ina226 on xilinx platform when hwmon
> >> driver is used. We have board for battery monitoring with shunt resistor
> >> setup to 10 Ohm which is out of config value in hwmon driver. I have
> > 
> > Took me a while to understand that you mean 10 Ohm, not mOhm.
> 
> yes.
> 
> > Well, yes, that is a bit large. I'd be open to accept a patch fixing that,
> > though I don't immediately know how to update the devicetree property (and,
> > unless I am missing something, the iio driver has the same problem).
> 
> There is shunt-resistor property in uOhm that's why 10 Ohm is like this
> shunt-resistor = <10000000>;
> 

Yes, I know, but that applies to both hwmon and iio.  What am I missing ?
Is there some overflow condition in the hwmon driver ? If yes, that should
be easy to fix.

> > 
> >> temporary code to workaround this but I have also found that ina226 is
> >> supported via iio framework. I have seen that Baylibre was trying to add
> >> generic iio support to sigrok.
> >> http://wiki.baylibre.com/doku.php?id=acme:oldstart
> >>
> >> I expect you wanted to use sigrok also for ina226.
> >>
> >> Anyway my question is if there is any standard tool which is capable to
> >> calculate and show information from iio ina226 chip which is can be used
> >> instead of lm-sensors and hwmon driver.
> >>
> >> I would expect that iio-hwmon could be also used but didn't try that yet
> >> with ina226 chip.
> >>
> > 
> > I don't immediately see why iio-hwmon couldn't be used. Also, if you don't
> > use the ina226 as hardware monitoring device, iio would be a more
> > appropriate
> > solution anyway.
> 
> I have tried this and found that IIO_POWER is not exported via iio-hwmon
> driver.

Probably IIO_POWER didn't exist when the iio-hwmon bridge was written.
Patches welcome.

> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
> /tree/drivers/hwmon/iio_hwmon.c?h=next-20190809#n104
> 
> It is easy to add because ina226 iio export power via channel 2
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/iio/adc/ina2xx-adc.c?h=next-20190809#n690
> 
> Also dt description is easy to add. + iio-channels = <1>; to ina226 dt node.
>        iio-hwmon {
>                compatible = "iio-hwmon";
>                io-channels = <&ps_pmbus 1>, <&ps_pmbus 2>, <&ps_pmbus 3>;
>        };
> 
> > 
> > FWIW, we should actually remove the in22xx hwmon driver at some point and
> > ask users to use the iio driver combined with the iio-hwmon bridge instead
> > (after making sure that the iio driver combined with the iio-hwmon bridge
> > provides the same functionality).
> 
> The functionality is likely the same but I would expect that with this
> new driver we should get something more. Especially that sigrok
> connection looks interesting.

Sorry, which new driver, and what is "something more" ?

Thanks,
Guenter

> In our system we have SoC which have a lot of ina226 which monitors the
> second SoC and would be nice to get precise information or graphs out of
> it via standard user space tools or directly to web page.
> 
> Thanks,
> Michal
>