Add a function to read the elements of the adxl345 FIFO. This will
flush the FIFO, and brings it into a ready state. The read out
is used to read the elemnts and to reset the fifo again. The cleanup
equally needs a read on the INT_SOURCE register.

Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
---
 drivers/iio/accel/adxl345_core.c | 40 ++++++++++++++++++++++++++++++--
 1 file changed, 38 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/accel/adxl345_core.c b/drivers/iio/accel/adxl345_core.c
index 508de81bb9..40e78dbdb0 100644
--- a/drivers/iio/accel/adxl345_core.c
+++ b/drivers/iio/accel/adxl345_core.c
@@ -140,6 +140,8 @@ struct adxl34x_state {
 	const struct adxl345_chip_info *info;
 	struct regmap *regmap;
 	struct adxl34x_platform_data data;  /* watermark, fifo_mode, etc */
+
+	__le16 fifo_buf[3 * ADXL34x_FIFO_SIZE] __aligned(IIO_DMA_MINALIGN);
 	u8 int_map;
 	bool fifo_delay; /* delay: delay is needed for SPI */
 	u8 intio;
@@ -323,6 +325,37 @@ static const struct attribute_group adxl345_attrs_group = {
 	.attrs = adxl345_attrs,
 };
 
+/**
+ * adxl345_get_fifo_entries() - Read number of FIFO entries into *fifo_entries.
+ * @st: The initialized state instance of this driver.
+ * @fifo_entries: A field to be initialized by this function with the number of
+ * FIFO entries.
+ *
+ * Since one read on the FIFO is reading all three axis, X, Y and Z in one, the
+ * number of FIFO entries corresponds to the number of triples of those values.
+ * Note, this sensor does not support treating any axis individually, or
+ * exclude them from measuring.
+ *
+ * Return: 0 or error value.
+ */
+static int adxl345_get_fifo_entries(struct adxl34x_state *st, int *fifo_entries)
+{
+	unsigned int regval = 0;
+	int ret;
+
+	ret = regmap_read(st->regmap, ADXL345_REG_FIFO_STATUS, &regval);
+	if (ret) {
+		pr_warn("%s(): Failed to read FIFO_STATUS register\n", __func__);
+		*fifo_entries = 0;
+		return ret;
+	}
+
+	*fifo_entries = 0x3f & regval;
+	pr_debug("%s(): fifo_entries %d\n", __func__, *fifo_entries);
+
+	return 0;
+}
+
 static const struct iio_buffer_setup_ops adxl345_buffer_ops = {
 };
 
@@ -363,6 +396,7 @@ static irqreturn_t adxl345_trigger_handler(int irq, void *p)
 	struct iio_dev *indio_dev = ((struct iio_poll_func *) p)->indio_dev;
 	struct adxl34x_state *st = iio_priv(indio_dev);
 	u8 int_stat;
+	int fifo_entries;
 	int ret;
 
 	ret = adxl345_get_status(st, &int_stat);
@@ -380,9 +414,11 @@ static irqreturn_t adxl345_trigger_handler(int irq, void *p)
 		goto done;
 	}
 
-	if (int_stat & (ADXL345_INT_DATA_READY | ADXL345_INT_WATERMARK))
+	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:
 
-- 
2.39.5