Re: [PATCH 1/5] dt-bindings: iio: mcp9600: Add compatible for microchip,mcp9601

[Ben Collins <ben.collins@linux.dev>]

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On Sun, Aug 17, 2025 at 05:02:49PM -0500, Ben Collins wrote:
> On Sun, Aug 17, 2025 at 12:59:48PM -0500, David Lechner wrote:
> > On 8/17/25 12:34 PM, Ben Collins wrote:
> > > On Sun, Aug 17, 2025 at 11:51:22AM -0500, David Lechner wrote:
> > >> On 8/17/25 11:37 AM, Ben Collins wrote:
> > >>> On Sat, Aug 16, 2025 at 01:55:31PM -0500, David Lechner wrote:
> > >>>> On 8/16/25 4:58 AM, Jonathan Cameron wrote:
> > >>>>> On Fri, 15 Aug 2025 16:46:03 +0000
> > >>>>> Ben Collins <bcollins@watter.com> wrote:
> > >>>>>
> > >>>>>> The mcp9600 driver supports the mcp9601 chip, but complains about not
> > >>>>>> recognizing the device id on probe. A separate patch...
> > >>>>>>
> > >>>>>> 	iio: mcp9600: Recognize chip id for mcp9601
> > >>>>>>
> > >>>>>> ...addresses this. This patch updates the dt-bindings for this chip to
> > >>>>>> reflect the change to allow explicitly setting microchip,mcp9601 as
> > >>>>>> the expected chip type.
> > >>>>>>
> > >>>>>> The mcp9601 also supports features not found on the mcp9600, so this
> > >>>>>> will also allow the driver to differentiate the support of these
> > >>>>>> features.
> > >>>>>
> > >>>>> If it's additional features only then you can still use a fallback
> > >>>>> compatible.  Intent being that a new DT vs old kernel still 'works'.
> > >>>>>
> > >>>>> Then for the driver on new kernels we match on the new compatible and
> > >>>>> support those new features.  Old kernel users get to keep the ID
> > >>>>> mismatch warning - they can upgrade if they want that to go away ;)
> > >>>>>
> > >>>>> Krzysztof raised the same point on v2 but I'm not seeing it addressed
> > >>>>> in that discussion.
> > >>>>
> > >>>> One could make the argument that these are not entirely fallback
> > >>>> compatible since bit 4 of the STATUS register has a different
> > >>>> meaning depending on if the chip is MCP9601/L01/RL01 or not.
> > >>>
> > >>> There are some nuances to this register between the two, but it can be
> > >>> used generically as "not in range" for both.
> > >>>
> > >>> My understanding from the docs is if VSENSE is connected on mcp9601,
> > >>> then it is explicitly open-circuit detection vs. short-circuit, which
> > >>> is bit 5.
> > >>>
> > >>>> Interestingly, the existing bindings include interrupts for
> > >>>> open circuit and short circuit alert pins. But these pins
> > >>>> also only exist on MCP9601/L01/RL01. If we decide these aren't
> > >>>> fallback compatible, then those properties should have the
> > >>>> proper constraints added as well.
> > >>>
> > >>> In my v4 patch, I'm going to remove the short/open circuit interrupts
> > >>> since they are not implemented, yet.
> > >>
> > >> Don't remove them from the devicetree bindings. Even if the Linux driver
> > >> doesn't use it, the bindings should be as complete as possible.
> > >>
> > >> https://docs.kernel.org/devicetree/bindings/writing-bindings.html
> > >>
> > > 
> > > I couldn't find anything that would easily describe this type of layout:
...
> > We usually do this the other way around. The base binding lists
> > all of the possibilities then an -if: constraint limits them
> > if needed.
> > 
> > 
> > So don't change what is there already and then add:
> > 
...
> This might be a little more complicated. I want to add a boolean for
> microchip,vsense so the SC/OC aren't even available without that flag
> being true (default false).
> 
> I could just assume that having the interrupts means this flag is true,
> but that doesn't cover the case where the interrupts might not be used
> or even wired up, but the SC/OC detection in the status register can be
> used.
> 
> I was going with this:
> 

Nevermind, I figured this out. I'll send v4 soon.


-- 
 Ben Collins
 https://libjwt.io
 https://github.com/benmcollins
 --
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