Re: Driver directory selection for Power Supply Status chip

[Thor Thayer <tthayer@opensource.altera.com>]

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.

Thank you for your reply!