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

Jonathan Cameron
2024-05-19T16:14:49Z

On Fri, 17 May 2024 10:10:49 +0200
Dimitri Fedrau <dima.fedrau@gmail.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@kernel.org>
> Signed-off-by: Dimitri Fedrau <dima.fedrau@gmail.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,
> },
> };
>