Re: [RFC] hwmon: add a driver for the temp/voltage sensor on PolarFire SoC

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

On 5/28/26 15:34, Conor Dooley wrote:
> On Wed, May 27, 2026 at 09:07:20PM -0700, Guenter Roeck wrote:
>> On Wed, May 27, 2026 at 10:06:11AM +0100, Conor Dooley wrote:
>>> From: Lars Randers <lranders@mail.dk>
>>>
>>> Add a driver for the temperature and voltage sensors on PolarFire SoC.
>>> The temperature reports how hot the die is, and the voltages are the
>>> SoC's 1.05, 1.8 and 2.5 volt rails respectively.
>>>
>>> The hardware supports alarms in theory, but there is an unconfirmed
>>> erratum that prevents clearing them once triggered, so no support is
>>> added.
>>>
>>> The hardware measures voltage with 16 bits, of which 1 is a sign bit and
>>> the remainder holds the voltage as a fixed point integer value. It's
>>> improbable that the hardware will work if the voltages are negative, so
>>> the driver ignores the sign bits.
>>>
>>> There's no dt support etc here because this is the child of a simple-mfd
>>> syscon.
>>>
>>> Signed-off-by: Lars Randers <lranders@mail.dk>
>>> Co-developed-by: Conor Dooley <conor.dooley@microchip.com>
>>> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
>>> ---
>>> Guenter, there's one question here about the unit that update_interval
>>> is in, I didn't see anyone else using us, but I assume that's okay since
>>> the resolution that ms would give would be 8 steps only?
>>> RFC cos the question is also in the driver as a comment.
>>>
>>
>> That just came up in a different context. We'll add a new standard attribute
>> update_interval_us. The existing attribute MUST use ms. Everything else
>> would be an ABI violation.
> 
> Cool. Sounds like Ferdinand is working on that based on the other
> thread.
> 
> Do you think I should support both update_interval and update_interval_us in
> this driver?
> 

I have been thinking about only supporting one for a given driver, but that
doesn't work because there are existing drivers which would benefit from
supporting microsecond-based intervals, so both it is (unless you want to
wait for _us support to be available and then just support that).

> If yes, should I do the ms version now and add the us version later once
> Ferdinand's work is complete?
> 

Yes, that is what I would recommend.

Thanks,
Guenter