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

[Conor Dooley <conor@kernel.org>]

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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?

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

Cheers,
Conor.

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