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

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Message-ID: <20250816105825.35e69652@jic23-huawei>
Date: Sat, 16 Aug 2025 10:58:25 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Ben Collins <bcollins@...ter.com>
Cc: David Lechner <dlechner@...libre.com>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Andrew Hepp <andrew.hepp@...pp.dev>,
 linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] dt-bindings: iio: mcp9600: Add compatible for
 microchip,mcp9601

On Fri, 15 Aug 2025 16:46:03 +0000
Ben Collins <bcollins@...ter.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.

Jonathan

> 
> Signed-off-by: Ben Collins <bcollins@...ter.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@...pp.dev>
> @@ -14,7 +14,9 @@ description:
>  
>  properties:
>    compatible:
> -    const: microchip,mcp9600
> +    enum:
> +      - microchip,mcp9600
> +      - microchip,mcp9601
>  
>    reg:
>      maxItems: 1