On Tue, 10 Jun 2025 21:59:23 +0000
Lothar Rubusch <l.rubusch@xxxxxxxxx> wrote:
> The threshold for tap detection was still not scaled. The datasheet sets
> a scale factor of 62.5mg/LSB. Remove commit about not scaled threshold
> for tap detection, and apply scaling to it.
>
Given tap detection algorithms are not generally well defined and not a simple
threshold (generally) what scaling should we be aiming for here?
Even if it were a simple threshold, when a channel provides _raw the
expectation is that event config is vs _raw, not the base units.
So if this doesn't care about the current fullscale range (which the
comment implied was the case) it would need to rescale when the
IIO_INFO_SCALE changes.
That comment is I think indicating we decided to gloss over the
detail because it's going into a (potentially) non trivial algorithm anyway.
Jonathan
> Signed-off-by: Lothar Rubusch <l.rubusch@xxxxxxxxx>
> ---
> drivers/iio/accel/adxl345_core.c | 11 +++++------
> 1 file changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/iio/accel/adxl345_core.c b/drivers/iio/accel/adxl345_core.c
> index 7c093c0241de..d80efb68d113 100644
> --- a/drivers/iio/accel/adxl345_core.c
> +++ b/drivers/iio/accel/adxl345_core.c
> @@ -697,17 +697,15 @@ static int adxl345_read_event_value(struct iio_dev *indio_dev,
> switch (info) {
> case IIO_EV_INFO_VALUE:
> /*
> - * The scale factor would be 62.5mg/LSB (i.e. 0xFF = 16g) but
> - * not applied here. In context of this general purpose sensor,
> - * what imports is rather signal intensity than the absolute
> - * measured g value.
> + * Scale factor is 62.5mg/LSB i.e. 0xff = 16g
> */
> ret = regmap_read(st->regmap, ADXL345_REG_THRESH_TAP,
> &tap_threshold);
> if (ret)
> return ret;
> - *val = sign_extend32(tap_threshold, 7);
> - return IIO_VAL_INT;
> + *val = 62500 * sign_extend32(tap_threshold, 7);
> + *val2 = MICRO;
> + return IIO_VAL_FRACTIONAL;
> case IIO_EV_INFO_TIMEOUT:
> *val = st->tap_duration_us;
> *val2 = 1000000;
> @@ -746,6 +744,7 @@ static int adxl345_write_event_value(struct iio_dev *indio_dev,
> case IIO_EV_TYPE_GESTURE:
> switch (info) {
> case IIO_EV_INFO_VALUE:
> + val = DIV_ROUND_CLOSEST(val * MICRO + val2, 62500);
> ret = regmap_write(st->regmap, ADXL345_REG_THRESH_TAP,
> min(val, 0xFF));
> if (ret)
