Re: [PATCH v2 1/3] iio: Add IIO_DENSITY channel type

[David Lechner <dlechner@baylibre.com>]

On 6/12/25 5:07 AM, surajsonawane0215@gmail.com wrote:
> From: Suraj Sonawane <surajsonawane0215@gmail.com>
> 
> Add IIO_DENSITY channel type for particulate matter sensors,
> with base units of grams per cubic meter (g/m³). This is needed
> for optical dust sensors like the Sharp GP2Y1010AU0F that measure
> airborne particle concentration rather than raw voltage.
> 
> Signed-off-by: Suraj Sonawane <surajsonawane0215@gmail.com>
> ---
> V2: Initial version introducing IIO_DENSITY channel type
> 
>  Documentation/ABI/testing/sysfs-bus-iio | 8 ++++++++
>  include/uapi/linux/iio/types.h          | 1 +
>  2 files changed, 9 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
> index 190bfcc1e..9b1b538ce 100644
> --- a/Documentation/ABI/testing/sysfs-bus-iio
> +++ b/Documentation/ABI/testing/sysfs-bus-iio
> @@ -2383,3 +2383,11 @@ Description:
>  		Value representing the user's attention to the system expressed
>  		in units as percentage. This usually means if the user is
>  		looking at the screen or not.
> +
> +What:		/sys/bus/iio/devices/iio:deviceX/in_density_raw
> +KernelVersion:	6.15
> +Contact:	linux-iio@vger.kernel.org
> +Description:
> +		Raw reading from an optical dust sensor.
> +		This value is proportional to dust density in air,

I don't see why density would be specific to dust. We could make
this description more generic.

> +		with base units of g/m^3.
> +
> diff --git a/include/uapi/linux/iio/types.h b/include/uapi/linux/iio/types.h
> index 3eb0821af..e7d09ec0b 100644
> --- a/include/uapi/linux/iio/types.h
> +++ b/include/uapi/linux/iio/types.h
> @@ -37,6 +37,7 @@ enum iio_chan_type {
>  	IIO_DISTANCE,
>  	IIO_VELOCITY,
>  	IIO_CONCENTRATION,
> +	IIO_DENSITY,

This is part of the userspace ABI, new items have to be added
to the end. We can't change the meaning of the numeric values.

>  	IIO_RESISTANCE,
>  	IIO_PH,
>  	IIO_UVINDEX,

There are also a couple more places where this new channel needs
be added as well. See [1] for an example (although density probably
doesn't need to be added to known events).

[1]: https://lore.kernel.org/all/20241101-hpd-v3-3-e9c80b7c7164@chromium.org/