[PATCH 4/4] iio: imu: inv_icm42600: do not read FIFO count for watermark it

From: Jean-Baptiste Maneyrol <[email protected]>

Optimize data reading for high frequencies by not reading FIFO
count in case of watermark interrupt. We already know there is
watermark samples in the FIFO and we need to not read more than
watermark samples for timestamping mechanism. Let's just read FIFO
data directly without reading FIFO count in this case.

Signed-off-by: Jean-Baptiste Maneyrol <[email protected]>
---
 drivers/iio/imu/inv_icm42600/inv_icm42600_buffer.c | 33 ++++++++++------------
 1 file changed, 15 insertions(+), 18 deletions(-)

diff --git a/drivers/iio/imu/inv_icm42600/inv_icm42600_buffer.c b/drivers/iio/imu/inv_icm42600/inv_icm42600_buffer.c
index 1428f18408ce..1410096f6e6d 100644
--- a/drivers/iio/imu/inv_icm42600/inv_icm42600_buffer.c
+++ b/drivers/iio/imu/inv_icm42600/inv_icm42600_buffer.c
@@ -474,24 +474,21 @@ int inv_icm42600_buffer_fifo_read(struct inv_icm42600_state *st,
 	st->fifo.nb.accel = 0;
 	st->fifo.nb.total = 0;
 
-	/* compute maximum FIFO read size (watermark for max = 0 interrupt case) */
-	if (max == 0)
-		max = st->fifo.watermark.value;
-	max_count = max * INV_ICM42600_FIFO_2SENSORS_PACKET_SIZE;
-
-	/* read FIFO count value */
-	raw_fifo_count = (__be16 *)st->buffer;
-	ret = regmap_bulk_read(st->map, INV_ICM42600_REG_FIFO_COUNT,
-			       raw_fifo_count, sizeof(*raw_fifo_count));
-	if (ret)
-		return ret;
-	st->fifo.count = be16_to_cpup(raw_fifo_count);
-
-	/* check and clamp FIFO count value */
-	if (st->fifo.count == 0)
-		return 0;
-	if (st->fifo.count > max_count)
-		st->fifo.count = max_count;
+	/* read watermark samples for interrupt case (max = 0) or read FIFO count */
+	if (max == 0) {
+		st->fifo.count = st->fifo.watermark.value *
+				 INV_ICM42600_FIFO_2SENSORS_PACKET_SIZE;
+	} else {
+		raw_fifo_count = (__be16 *)st->buffer;
+		ret = regmap_bulk_read(st->map, INV_ICM42600_REG_FIFO_COUNT,
+					raw_fifo_count, sizeof(*raw_fifo_count));
+		if (ret)
+			return ret;
+		max_count = max * INV_ICM42600_FIFO_2SENSORS_PACKET_SIZE;
+		st->fifo.count = min(be16_to_cpup(raw_fifo_count), max_count);
+		if (st->fifo.count == 0)
+			return 0;
+	}
 
 	/* read all FIFO data in internal buffer */
 	ret = regmap_noinc_read(st->map, INV_ICM42600_REG_FIFO_DATA,

-- 
2.55.0