Re: [PATCH v3 08/15] iio: accel: adxl345: add double tap suppress bit

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 20 Feb 2025 10:42:27 +0000
Lothar Rubusch <l.rubusch@gmail.com> wrote:

> Set the suppress bit feature to the double tap detection, whenever
> double tap is enabled.
> 
> Any tap event is defined by a rising signal edge above threshold, i.e.
> duration time starts counting; and the falling edge under threshold
> within duration time, i.e. then the tap event is issued. This means
> duration is used individually for each tap event.
> 
> For double tap detection after a single tap, a latency time needs to be
> specified. Usually tap events, i.e. spikes above and returning below
> threshold will be ignored within latency. After latency, the window
> time starts counting for a second tap detection which has to happen
> within a duration time.
> 
> If the suppress bit is not set, spikes within latency time are ignored.
> Setting the suppress bit will invalidate the double tap function. The
> sensor will thus be able to save the window time for double tap
> detection, and follow a more strict definition of what signal qualifies
> for a double tap.
> 
> In a summary having the suppress bit set, fewer signal spikes will be
> considered as double taps. This is an optional add on to double tap,
> thus a separate patch.
> 
> Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
> ---
>  drivers/iio/accel/adxl345_core.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/iio/accel/adxl345_core.c b/drivers/iio/accel/adxl345_core.c
> index c014bdf84e66..10cd81dd08bb 100644
> --- a/drivers/iio/accel/adxl345_core.c
> +++ b/drivers/iio/accel/adxl345_core.c
> @@ -34,6 +34,7 @@
>  #define ADXL345_INT2			1
>  
>  #define ADXL345_REG_TAP_AXIS_MSK	GENMASK(2, 0)
> +#define ADXL345_REG_TAP_SUPPRESS_MSK	BIT(3)
>  
>  enum adxl345_axis {
>  	ADXL345_Z_EN = BIT(0),
> @@ -258,6 +259,18 @@ static int adxl345_set_singletap_en(struct adxl345_state *st,
>  
>  static int adxl345_set_doubletap_en(struct adxl345_state *st, bool en)
>  {
> +	int ret;
> +
> +	/*
> +	 * generally suppress detection of spikes during the latency period as
Local style has large comments as sentences so capital letter at start and a full stop
at the end preferred.

> +	 * double taps here, this is fully optional for double tap detection
> +	 */
> +	ret = regmap_update_bits(st->regmap, ADXL345_REG_TAP_AXIS,
> +				 ADXL345_REG_TAP_SUPPRESS_MSK,
> +				 en ? ADXL345_TAP_SUPPRESS : 0x00);
> +	if (ret)
> +		return ret;
> +
>  	return _adxl345_set_tap_int(st, ADXL345_DOUBLE_TAP, en);
>  }
>