Add a function to empty the FIFO and reset the INT_SOURCE register.
Reading out is used to reset the fifo again. For cleanup also a read
on the INT_SOURCE register is needed to allow the adxl345 to issue
interrupts again. Without clearing the fields no further interrupts
will happen.

Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
---
 drivers/iio/accel/adxl345_core.c | 75 ++++++++++++++++++++++++++++----
 1 file changed, 67 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/accel/adxl345_core.c b/drivers/iio/accel/adxl345_core.c
index 40e78dbdb0..82bd5c2b78 100644
--- a/drivers/iio/accel/adxl345_core.c
+++ b/drivers/iio/accel/adxl345_core.c
@@ -356,6 +356,61 @@ static int adxl345_get_fifo_entries(struct adxl34x_state *st, int *fifo_entries)
 	return 0;
 }
 
+/**
+ * adxl345_read_fifo_elements() - Read fifo_entries number of elements.
+ * @st: The instance of the state object of this sensor.
+ * @fifo_entries: The number of lines in the FIFO referred to as fifo_entry,
+ * a fifo_entry has 3 elements for X, Y and Z direction of 2 bytes each.
+ *
+ * The FIFO of the sensor is read linewise. The read measurement values are
+ * queued in the corresponding data structure in *st.
+ *
+ * It is recommended that a multiple-byte read of all registers be performed to
+ * prevent a change in data between reads of sequential registers. That is to
+ * read out the data registers X0, X1, Y0, Y1, Z0, Z1 at once.
+ *
+ * Return: 0 or error value.
+ */
+static int adxl345_read_fifo_elements(struct adxl34x_state *st, int fifo_entries)
+{
+	size_t count, ndirs = 3;
+	int i, ret;
+
+	count = 2 * ndirs; /* 2 byte per direction */
+	for (i = 0; i < fifo_entries; i++) {
+		ret = regmap_noinc_read(st->regmap, ADXL345_REG_XYZ_BASE,
+				st->fifo_buf + (i * count / 2), count);
+		if (ret) {
+			pr_warn("%s(): regmap_noinc_read() failed\n", __func__);
+			return -EFAULT;
+		}
+	}
+
+	return 0;
+}
+
+/**
+ * adxl345_empty_fifo() - Empty the FIFO.
+ * @st: The instance to the state object of the sensor.
+ *
+ * Reading all elements of the FIFO linewise empties the FIFO. Reading th
+ * interrupt source register resets the sensor. This is needed also in case of
+ * overflow or error handling to reenable the sensor to issue interrupts.
+ */
+static void adxl345_empty_fifo(struct adxl34x_state *st)
+{
+	int regval;
+	int fifo_entries;
+
+	/* In case the HW is not "clean" just read out remaining elements */
+	adxl345_get_fifo_entries(st, &fifo_entries);
+	if (fifo_entries > 0)
+		adxl345_read_fifo_elements(st, fifo_entries);
+
+	/* Reset the INT_SOURCE register by reading the register */
+	regmap_read(st->regmap, ADXL345_REG_INT_SOURCE, &regval);
+}
+
 static const struct iio_buffer_setup_ops adxl345_buffer_ops = {
 };
 
@@ -401,30 +456,34 @@ static irqreturn_t adxl345_trigger_handler(int irq, void *p)
 
 	ret = adxl345_get_status(st, &int_stat);
 	if (ret < 0)
-		goto done;
+		goto err;
 
 	/* Ignore already read event by reissued too fast */
 	if (int_stat == 0x0)
-		goto done;
+		goto err;
 
 	/* evaluation */
 
 	if (int_stat & ADXL345_INT_OVERRUN) {
 		pr_debug("%s(): OVERRUN event detected\n", __func__);
-		goto done;
+		goto err;
 	}
 
 	if (int_stat & (ADXL345_INT_DATA_READY | ADXL345_INT_WATERMARK)) {
 		pr_debug("%s(): WATERMARK or DATA_READY event detected\n", __func__);
 		if (adxl345_get_fifo_entries(st, &fifo_entries) < 0)
-			goto done;
-	}
-	goto done;
-done:
+			goto err;
 
-	if (indio_dev)
 		iio_trigger_notify_done(indio_dev->trig);
+	}
 
+	goto done;
+err:
+	iio_trigger_notify_done(indio_dev->trig);
+	adxl345_empty_fifo(st);
+	return IRQ_NONE;
+
+done:
 	return IRQ_HANDLED;
 }
 
-- 
2.39.5