[PATCH v10 2/4] iio: pressure: dps310: derive the drain interval from the watermark

[Rupesh Majhi <zoone.rupert@gmail.com>]

The drain interval only tracked how fast the FIFO fills, so a small
watermark still waited half a FIFO for its samples. Take the watermark
as the number of scans to wait for, but never drain slower than half a
fill.

Assisted-by: LLM
Signed-off-by: Rupesh Majhi <zoone.rupert@gmail.com>
---
 drivers/iio/pressure/dps310.c | 35 +++++++++++++++++++++++++++++++----
 1 file changed, 31 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/pressure/dps310.c b/drivers/iio/pressure/dps310.c
index 53ebf6962eba..82bbfd097cd7 100644
--- a/drivers/iio/pressure/dps310.c
+++ b/drivers/iio/pressure/dps310.c
@@ -115,6 +115,7 @@ struct dps310_data {
 	s32 *fifo_hold;
 	unsigned int fifo_hold_max;
 	unsigned int fifo_held;
+	unsigned int watermark;
 	unsigned int drain_interval_ms;
 	s32 fifo_temp_raw;
 };
@@ -982,13 +983,28 @@ static int dps310_fifo_set_enable(struct dps310_data *data, bool enable)
  * No interrupt pin is wired in tree, so drain on a timer. Both measurements
  * share the entries, so they fill it together.
  */
-static unsigned int dps310_fifo_interval(int prs_rate, int tmp_rate)
+static unsigned int dps310_fifo_interval(struct dps310_data *data, int prs_rate,
+					 int tmp_rate)
 {
-	unsigned int fill_ms;
+	unsigned int fill_ms, want_ms;
+	int scan_rate;
 
 	fill_ms = MSEC_PER_SEC * DPS310_FIFO_DEPTH / (prs_rate + tmp_rate);
 
-	return clamp(fill_ms / 2, DPS310_DRAIN_MIN_MS, DPS310_DRAIN_MAX_MS);
+	/*
+	 * There is no hardware watermark, so take it as the number of scans
+	 * the user will wait for and drain at that rate. Scans come from
+	 * whichever measurement drives them.
+	 */
+	if (test_bit(DPS310_SCAN_PRESSURE, data->iio->active_scan_mask))
+		scan_rate = prs_rate;
+	else
+		scan_rate = tmp_rate;
+
+	want_ms = data->watermark * MSEC_PER_SEC / scan_rate;
+
+	return clamp(min(want_ms, fill_ms / 2), DPS310_DRAIN_MIN_MS,
+		     DPS310_DRAIN_MAX_MS);
 }
 
 /* Returns which measurement the entry came from, or a negative error */
@@ -1168,6 +1184,15 @@ static int dps310_fifo_hold_alloc(struct dps310_data *data, int prs_rate,
 	return 0;
 }
 
+static int dps310_hwfifo_set_watermark(struct iio_dev *iio, unsigned int val)
+{
+	struct dps310_data *data = iio_priv(iio);
+
+	data->watermark = clamp(val, 1, DPS310_FIFO_DEPTH);
+
+	return 0;
+}
+
 static int dps310_buffer_postenable(struct iio_dev *iio)
 {
 	struct dps310_data *data = iio_priv(iio);
@@ -1191,7 +1216,7 @@ static int dps310_buffer_postenable(struct iio_dev *iio)
 	if (rc)
 		goto err_unlock;
 
-	data->drain_interval_ms = dps310_fifo_interval(prs_rate, tmp_rate);
+	data->drain_interval_ms = dps310_fifo_interval(data, prs_rate, tmp_rate);
 
 	rc = dps310_fifo_hold_alloc(data, prs_rate, tmp_rate);
 	if (rc)
@@ -1299,6 +1324,7 @@ static const struct regmap_config dps310_regmap_config = {
 static const struct iio_info dps310_info = {
 	.read_raw = dps310_read_raw,
 	.write_raw = dps310_write_raw,
+	.hwfifo_set_watermark = dps310_hwfifo_set_watermark,
 };
 
 static int dps310_probe(struct i2c_client *client)
@@ -1315,6 +1341,7 @@ static int dps310_probe(struct i2c_client *client)
 	data = iio_priv(iio);
 	data->client = client;
 	data->iio = iio;
+	data->watermark = 1;
 	mutex_init(&data->lock);
 	INIT_DELAYED_WORK(&data->fifo_work, dps310_fifo_work);
 
-- 
2.43.0