Re: [PATCH v2] iio: accel: dmard09: Implement IIO_CHAN_INFO_SCALE

[Joshua Crofts]

On Fri, 10 Jul 2026 10:36:23 +0200
Mert Seftali <mertsftl@xxxxxxxxx> wrote:

> Reading the in_accel_scale attribute on the DMARD09 has always returned
> -EINVAL: the channels advertise scale via info_mask_shared_by_type so the
> IIO core exposes the attribute, but dmard09_read_raw() only handles
> IIO_CHAN_INFO_RAW, so a SCALE read falls through to 'default: return
> -EINVAL':
> 
>     $ cat .../iio:deviceX/in_accel_scale
>     cat: in_accel_scale: Invalid argument
> 
> leaving userspace with raw counts it cannot convert to m/s^2.
> 
> The driver was written from a vendor source [1] without a datasheet, and
> the scale was declared but never implemented. The vendor source carries
> the sensitivity: its conversion is
> 
>     acc = raw * GRAVITY_EARTH_1000 / sensitivity   (then / 1000 -> m/s^2)
> 
> with sensitivity = 32 and GRAVITY_EARTH_1000 = 9807 ("about
> (9.80665)*1000"), i.e. 32 counts correspond to 1 g.
> 
> That sensitivity applies to the value this driver already reports as raw:
> the vendor reduces each 16-bit sample to a signed 9-bit value, and the
> preparation in dmard09_read_raw() yields the same value. It is
> self-consistent: 256 counts / 32 = 8 g full scale, matching the +/-8g
> range.
> 
> Implement the scale derived from that sensitivity using standard gravity:
> 
>     scale = 9.80665 / 32 = 0.3064578125 m/s^2 per LSB
> 
> Link: https://github.com/minstrelsy/mediatek/blob/1f49d8c87b839651bc89afc870277e8e0f2e2d55/custom/common/kernel/accelerometer/dmard09/dmard09.c [1]
> Fixes: a4fa6509dda4 ("iio: accel: add support for the Domintech DMARD09 3-axis accelerometer")
> Signed-off-by: Mert Seftali <mertsftl@xxxxxxxxx>
> ---

Good thing that Jelle sent the vendor driver, LGTM.

Reviewed-by: Joshua Crofts <joshua.crofts1@xxxxxxxxx>

-- 
Kind regards

CJD