[PATCH v5 04/11] iio: accel: adxl345: set the tap suppress bit permanently

[Lothar Rubusch <l.rubusch@gmail.com>]

Set the suppress bit feature to the double tap detection, whenever
double tap is enabled. This impedes the suppress bit dangling in any
state, and thus varying in sensitivity for double tap detection.

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 | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/iio/accel/adxl345_core.c b/drivers/iio/accel/adxl345_core.c
index 9dee819d5252..52daf46c4acd 100644
--- a/drivers/iio/accel/adxl345_core.c
+++ b/drivers/iio/accel/adxl345_core.c
@@ -34,6 +34,8 @@
 #define ADXL345_INT2			1
 
 #define ADXL345_REG_TAP_AXIS_MSK	GENMASK(2, 0)
+#define ADXL345_REG_TAP_SUPPRESS_MSK	BIT(3)
+#define ADXL345_REG_TAP_SUPPRESS	BIT(3)
 
 #define ADXL345_TAP_Z_EN		BIT(0)
 #define ADXL345_TAP_Y_EN		BIT(1)
@@ -288,6 +290,18 @@ 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
+	 * 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_REG_TAP_SUPPRESS : 0x00);
+	if (ret)
+		return ret;
+
 	return _adxl345_set_tap_int(st, ADXL345_DOUBLE_TAP, en);
 }
 
-- 
2.39.5