Re: Driver directory selection for Power Supply Status chip

[Jonathan Cameron <jic23@kernel.org>]

On 18/04/16 20:43, Thor Thayer wrote:
> 
> 
> On 04/18/2016 11:41 AM, Lars-Peter Clausen wrote:
>> On 04/18/2016 06:14 PM, Thor Thayer wrote:
>>> Hi,
>>>
>>> The Arria10 System Resource chip (A10SR) is a SPI based MFD implementing a
>>> GPIO expander, reset controller, and power supply monitoring. I'm not sure
>>> where the driver for the A10SR power monitoring driver should reside and I'm
>>> hoping someone can offer some advice.
>>>
>>> I'd originally submitted the RFC to the HWMON list but the maintainer
>>> pointed out that it wasn't a good fit because the A10SR only indicates
>>> boolean power supply status - not the voltage level as required by HWMON.
>>>
>>> I read that IIO acts as a bridge between IO and HWMON but I'm also not sure
>>> this fits those drivers (although I did find some power supply supervistors
>>> there). It isn't quite a power supply supervisor - the A10SR is a comparator
>>> instead of an Analog-to-Digital Converter.
>>>
>>> One additional thing, the A10SR also had a number of enable bits for
>>> enabling devices external to Altera's SoC (but still on the development
>>> board). These don't quite fit into the reset controller framework but would
>>> seem to fit a MISC directory driver better.
>>>
>>> If neither IIO or MISC is a good fit, can someone suggest a more appropriate
>>> place?
>>
>> How does the device work, does it generate an interrupt when the voltage
>> level goes below the threshold? I'd like to pass the ball back and say that
>> this sounds like something that should go into hwmon.
>>
> 
> Good question but no, there is no interrupt.
> 
> The chip is actually a power supply sequencer for bringing up the
> power supplies in the correct order. Since the sequence, timings, and
> thresholds are hard coded in the chip and can't be changed
> programatically, I assume it was decided that a power fail interrupt
> was not needed. However, the status of the power (OK/Fail) can be
> read from the chip.
> 
> I was directed to look at Documentation/hwmon/sysfs-interface which
> states the units are in millivolts and I didn't see any references to
> a boolean output so I'm leaning away from hwmon.
That's one impressively uninformative output...  Hmm.
Not obvious where to put it - it doesn't fit in IIO really either.

Could report as a power supply?  There is 'health' support in there.
See Documentation/power/power_supply_class.txt
and include/linux/power_supply.h
though I'm not sure which type a fail on this would count as...
perhaps UNSPEC_FAILURE.

It's intended for batteries really - not sure how far you can stretch
that.

Cc'd linux-pm and maintainers.  Perhaps they will have a better idea!
> 
> Thank you for your reply!
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