Re: [PATCH v2 1/2] dt-bindings: iio: temperature: add support for MCP998X

[Conor Dooley <conor@kernel.org>]

[-- Attachment #1: Type: text/plain, Size: 2175 bytes --]

Jonathan,

On Mon, Jun 02, 2025 at 02:48:52PM +0000, Victor.Duicu@microchip.com wrote:
> On Fri, 2025-05-30 at 16:55 +0100, Conor Dooley wrote:
> > On Thu, May 29, 2025 at 01:13:38PM -0500, David Lechner wrote:
> > > On 5/29/25 4:36 AM, victor.duicu@microchip.com wrote:
> > > > From: Victor Duicu <victor.duicu@microchip.com>
> > > > +  microchip,recd12:
> > > > +    description:
> > > > +      Enable resistance error correction for external channels 1
> > > > and 2.
> > > > +      Omit this tag to disable REC for channels 1 and 2.
> > > > +    type: boolean
> > > > +
> > > > +  microchip,recd34:
> > > > +    description:
> > > > +      Enable resistance error correction for external channels 3
> > > > and 4.
> > > > +      Omit this tag to disable REC for channels 3 and 4.
> > 
> > Why are these two devicetree properties, rather than runtime
> > controls?
> 
> The parasitic resistance added to the series resistance is dependent
> only on the circuit. 
> It is possible for the chip and the transistor to be at some distance
> from each other. The manufacturer can approximate the error added and
> decide if resistance error correction should be applied.

I don't think I buy this line of argument. The property is not
describing the hardware, it's literally being used as a toggle for some
software feature. It'd be more acceptable if it indicated that the chip
and transistor were distant, leaving software to make a decision on what
that meant. One user (say bsd) might want decide that the driver should
always enable it, but another (say linux) might expose it as a control
to userspace defaulting based the dt property.
Additionally, the name of the property is pretty awful, and does not
even hint at what it's doing - and there's no mention of why channel 1/2
and 3/4 are bound together.

> The user cannot influence the parasitic resistance nor calculate it.

I don't think that's super relevant here, since the property has nothing
to do with influencing or calculating the value. I meant deciding whether
or not the correction is applied, just as the dt property you propose
does now.

Cheers,
Conor.

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]