Re: [PATCH 2/2] iio: imu: lsm6dsx: Add alternative ACPI mount matrix retrieval

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 22 Dec 2025 21:53:51 -0500
Samuel Dionne-Riel <samuel@dionne-riel.com> wrote:

> This uses the SLA0 matrix, which is how the SMOCF05 configuration
> exposes the mounting information for the accelerometer.
> 
> On a limited sample size of one (1) unit, the SLG0 matrix is the
> identity matrix. It is unknown how the SLG0 mounting matrix would
> logically affect the data, if it differed from the identity matrix.
> After all, the IMU is mounted as one single unit, its mounting can't
> differ on the gyroscope compared to the accelerometer.
Hi Samuel

*sigh* More ACPI creativity.  Thanks for your detailed investigation.

I'm a bit curious why they didn't use the ones Microsoft defined
for windows but otherwise fine to support this.  A comment on the
approach below.

> 
> Signed-off-by: Samuel Dionne-Riel <samuel@dionne-riel.com>
> ---
>  drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> index 49ac17806e720..4bf1f7f7552d1 100644
> --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> @@ -2707,6 +2707,12 @@ int st_lsm6dsx_probe(struct device *dev, int irq, int hw_id,
>  			return err;
>  	}
>  
> +	if (!iio_read_acpi_mount_matrix(hw->dev, &hw->orientation, "SLA0")) {
> +		err = iio_read_mount_matrix(hw->dev, &hw->orientation);
Whilst this 'works' this internal call is pointless as we already did this
if there was not match on ROTM just off the context visible here.

I think the way to do this cleanly is probably to have an st_read_acpi_mount_matrix()
helper that tries ROTM and SLA0 in turn.  Then have something like;

	if(!st_read_acpi_mount_matrix(hw->dev, &hw->orientation)) {
		err = iio_read_mount_matrix(hw->dev, &hw->orientation);
		if (err)
			return err;


	}
> +		if (err)
> +			return err;
> +	}
> +
>  	for (i = 0; i < ST_LSM6DSX_ID_MAX; i++) {
>  		if (!hw->iio_devs[i])
>  			continue;