Re: [PATCH v1 3/5] ABI: iio: add new ABI doc for mhz19b

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Thu,  3 Apr 2025 14:32:23 +0900
Gyeyoung Baek <gye976@gmail.com> wrote:

> Add support for winsen MHZ19B CO2 sensor.
> 
> Signed-off-by: Gyeyoung Baek <gye976@gmail.com>
> ---
>  Documentation/ABI/testing/sysfs-bus-iio-chemical-mhz19b | 7 +++++++
>  1 file changed, 7 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-chemical-mhz19b
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-iio-chemical-mhz19b b/Documentation/ABI/testing/sysfs-bus-iio-chemical-mhz19b
> new file mode 100644
> index 000000000000..6cdfd34be016
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-bus-iio-chemical-mhz19b
> @@ -0,0 +1,7 @@
> +What:		/sys/bus/iio/devices/co2_range
> +Date:		April 2025
> +KernelVersion:	6.14
> +Contact:	Gyeyoung Baek <gye976@gmail.com>
> +Description:
> +		Writing a value adjust maximum measurable PPM.
> +		should be 2000 or 5000.

I haven't checked but assume this also results in a scaling of the
measure _raw values?  If so the control should be via the standard
ABI scale.  If you need to be able to establish the range, provide
the _available for the _raw via the read_avail() callback and setting
appropriate bit in info_mask_separate_available

General rule is don't introduce new ABI unless it is impossible to
provide the same information via existing interfaces.  The decision
to use scale rather than range info to control channel scaling was
made a very long time ago and having a mixture of the two would
make for very complex userspace code.

Jonathan

> --
> 2.34.1
> 
>