linux-kernel - Re: [PATCH v2 1/2] iio: temperature: mcp9600: Provide index for both channels

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Date: Sun, 19 May 2024 17:14:38 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Dimitri Fedrau <dima.fedrau@...il.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Andrew Hepp
 <andrew.hepp@...pp.dev>, Marcelo Schmitt <marcelo.schmitt1@...il.com>,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, Nuno
 Sá <nuno.sa@...log.com>
Subject: Re: [PATCH v2 1/2] iio: temperature: mcp9600: Provide index for
 both channels

On Fri, 17 May 2024 10:10:49 +0200
Dimitri Fedrau <dima.fedrau@...il.com> wrote:

> The mapping from cold junction to ambient temperature is inaccurate. We
> provide an index for hot and cold junction temperatures.
> 
> Suggested-by: Jonathan Cameron <jic23@...nel.org>
> Signed-off-by: Dimitri Fedrau <dima.fedrau@...il.com>
Hi Dmitri,

I'm not sure you replied to the question in previous review of what
sysfs files exist for this device.  Whilst I am at least a little
open to changing the ABI, I'd like to fully understand what
is currently presented and why iio_info is having trouble with it.

I also want an ack from Andrew on this one given might break it existing
usage.

The current interface is perhaps less than ideal, but I don't think it
is wrong as such. Whilst I wasn't particularly keen on the cold junction
== ambient I'm not sure moving to just indexed is an improvement.
Hence looking for input from Andrew. +CC Nuno as someone who is both
active in IIO and has written thermocouple front end drivers in
the past.

Jonathan


> ---
>  drivers/iio/temperature/mcp9600.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/temperature/mcp9600.c b/drivers/iio/temperature/mcp9600.c
> index 46845804292b..22451d1d9e1f 100644
> --- a/drivers/iio/temperature/mcp9600.c
> +++ b/drivers/iio/temperature/mcp9600.c
> @@ -14,6 +14,9 @@
>  
>  #include <linux/iio/iio.h>
>  
> +#define MCP9600_CHAN_HOT_JUNCTION	0
> +#define MCP9600_CHAN_COLD_JUNCTION	1
> +
>  /* MCP9600 registers */
>  #define MCP9600_HOT_JUNCTION 0x0
>  #define MCP9600_COLD_JUNCTION 0x2
> @@ -25,17 +28,19 @@
>  static const struct iio_chan_spec mcp9600_channels[] = {
>  	{
>  		.type = IIO_TEMP,
> +		.channel = MCP9600_CHAN_HOT_JUNCTION,
>  		.address = MCP9600_HOT_JUNCTION,
>  		.info_mask_separate =
>  			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
> +		.indexed = 1,
>  	},
>  	{
>  		.type = IIO_TEMP,
> +		.channel = MCP9600_CHAN_COLD_JUNCTION,
>  		.address = MCP9600_COLD_JUNCTION,
> -		.channel2 = IIO_MOD_TEMP_AMBIENT,
> -		.modified = 1,
>  		.info_mask_separate =
>  			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
> +		.indexed = 1,
>  	},
>  };
>