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

[David Lechner <dlechner@baylibre.com>]

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.

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.

> 
> Jonathan
> 
>>
>> Signed-off-by: Ben Collins <bcollins@watter.com>
>> ---
>>  .../bindings/iio/temperature/microchip,mcp9600.yaml         | 6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/iio/temperature/microchip,mcp9600.yaml b/Documentation/devicetree/bindings/iio/temperature/microchip,mcp9600.yaml
>> index d2cafa38a5442..d8af0912ce886 100644
>> --- a/Documentation/devicetree/bindings/iio/temperature/microchip,mcp9600.yaml
>> +++ b/Documentation/devicetree/bindings/iio/temperature/microchip,mcp9600.yaml
>> @@ -4,7 +4,7 @@
>>  $id: http://devicetree.org/schemas/iio/temperature/microchip,mcp9600.yaml#
>>  $schema: http://devicetree.org/meta-schemas/core.yaml#
>>  
>> -title: Microchip MCP9600 thermocouple EMF converter
>> +title: Microchip MCP9600 and similar thermocouple EMF converters
>>  
>>  maintainers:
>>    - Andrew Hepp <andrew.hepp@ahepp.dev>
>> @@ -14,7 +14,9 @@ description:
>>  
>>  properties:
>>    compatible:
>> -    const: microchip,mcp9600
>> +    enum:
>> +      - microchip,mcp9600
>> +      - microchip,mcp9601
>>  
>>    reg:
>>      maxItems: 1
>