[PATCH v10 0/4] iio: pressure: dps310: hardware FIFO support

[PATCH v10 0/4] iio: pressure: dps310: hardware FIFO support

[Rupesh Majhi]

Rest of FIFO series, on iio/togreg which has 1-6 and 10 of v8.

Since v9, from Andy's review:
 - patch 1: include time.h, one continue in drain temperature branch
 - patch 4, new: lockdep_assert_held() next to every __must_hold(),
   including 12 in applied code

Pressure overflow fix is now at v2:
https://lore.kernel.org/linux-iio/20260930085819.886339-1-zoone.rupert@gmail.com/

Retested on DPS310 with BeagleBone Black: buffer enables, flush race,
bad held entry, temperature-only capture. Lockdep asserts tested under
QEMU with PROVE_LOCKING, including a build with a lock left out.

v9: https://lore.kernel.org/linux-iio/20260928211127.641828-1-zoone.rupert@gmail.com/

Rupesh Majhi (4):
  iio: pressure: dps310: read buffered samples from the hardware FIFO
  iio: pressure: dps310: derive the drain interval from the watermark
  iio: pressure: dps310: implement .hwfifo_flush_to_buffer()
  iio: pressure: dps310: assert the lock at runtime too

 drivers/iio/pressure/dps310.c | 449 +++++++++++++++++++++++++++++++++-
 1 file changed, 439 insertions(+), 10 deletions(-)


base-commit: a3b3580713f3ac5a32dc2874ee546828977a1d68
-- 
2.43.0

[PATCH v10 1/4] iio: pressure: dps310: read buffered samples from the hardware FIFO

[Rupesh Majhi]

DPS310 has a 32-entry FIFO shared by both measurements. Drain it from a
work item and push what it held, so buffered capture needs no trigger.
Nothing in tree wires the interrupt pin, so the work rearms itself at
half the FIFO fill time.

Each entry carries one measurement, so a pressure entry is compensated
with the temperature ahead of it. Pressure read before a session's first
temperature is held until one arrives rather than dropped, so the first
push can wait a temperature period.

FIFO entries are not timestamped, so postenable refuses the timestamp
channel unless a trigger is attached.

Tested on a DPS310 on a BeagleBone Black.

Assisted-by: LLM
Signed-off-by: Rupesh Majhi <zoone.rupert@gmail.com>
---
 drivers/iio/pressure/dps310.c | 351 +++++++++++++++++++++++++++++++++-
 1 file changed, 341 insertions(+), 10 deletions(-)

diff --git a/drivers/iio/pressure/dps310.c b/drivers/iio/pressure/dps310.c
index 85df58ac1809..53ebf6962eba 100644
--- a/drivers/iio/pressure/dps310.c
+++ b/drivers/iio/pressure/dps310.c
@@ -2,16 +2,11 @@
 // Copyright IBM Corp 2019
 /*
  * The DPS310 is a barometric pressure and temperature sensor.
- * Currently only reading a single temperature is supported by
- * this driver.
  *
  * https://www.infineon.com/dgdl/?fileId=5546d462576f34750157750826c42242
  *
  * Temperature calculation:
  *   c0 * 0.5 + c1 * T_raw / kT °C
- *
- * TODO:
- *  - Optionally support the FIFO
  */
 
 #include <linux/cleanup.h>
@@ -20,7 +15,11 @@
 #include <linux/math64.h>
 #include <linux/module.h>
 #include <linux/regmap.h>
+#include <linux/slab.h>
+#include <linux/time.h>
 #include <linux/unaligned.h>
+#include <linux/units.h>
+#include <linux/workqueue.h>
 
 #include <linux/iio/buffer.h>
 #include <linux/iio/iio.h>
@@ -59,9 +58,22 @@
 #define  DPS310_FIFO_EN		BIT(1)
 #define  DPS310_SPI_EN		BIT(0)
 #define DPS310_RESET		0x0c
+#define  DPS310_FIFO_FLUSH	BIT(7)
 #define  DPS310_RESET_MAGIC	0x09
 #define DPS310_COEF_BASE	0x10
 
+/* Section 4.8: 32 shared entries. Stops when full, so late drains lose data */
+#define DPS310_FIFO_DEPTH	32
+
+/* Read back once the FIFO is empty */
+#define DPS310_FIFO_EMPTY_VAL	0x800000
+
+/* LSB tags which measurement produced the entry */
+#define DPS310_FIFO_TAG_PRS	BIT(0)
+
+#define DPS310_DRAIN_MIN_MS	20
+#define DPS310_DRAIN_MAX_MS	(2 * MSEC_PER_SEC)
+
 /* Make sure sleep time is <= 30ms for usleep_range */
 #define DPS310_POLL_SLEEP_US(t)		min(30000, (t) / 8)
 /* Silently handle error in rate value here */
@@ -95,6 +107,22 @@ struct dps310_data {
 	s32 pressure_raw;
 	s32 temp_raw;
 	bool timeout_recovery_failed;
+	bool fifo_temp_valid;
+
+	/* Used only while the FIFO is enabled */
+	struct iio_dev *iio;
+	struct delayed_work fifo_work;
+	s32 *fifo_hold;
+	unsigned int fifo_hold_max;
+	unsigned int fifo_held;
+	unsigned int drain_interval_ms;
+	s32 fifo_temp_raw;
+};
+
+enum dps310_fifo_entry {
+	DPS310_FIFO_EMPTY,
+	DPS310_FIFO_TEMP,
+	DPS310_FIFO_PRESSURE,
 };
 
 enum dps310_scan_index {
@@ -937,6 +965,288 @@ static int dps310_fill_channels(struct dps310_data *data,
 	return 0;
 }
 
+static int dps310_fifo_hw_flush(struct dps310_data *data)
+	__must_hold(&data->lock)
+{
+	return regmap_write(data->regmap, DPS310_RESET, DPS310_FIFO_FLUSH);
+}
+
+static int dps310_fifo_set_enable(struct dps310_data *data, bool enable)
+	__must_hold(&data->lock)
+{
+	return regmap_assign_bits(data->regmap, DPS310_CFG_REG, DPS310_FIFO_EN,
+				  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)
+{
+	unsigned int fill_ms;
+
+	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);
+}
+
+/* Returns which measurement the entry came from, or a negative error */
+static int dps310_fifo_read_entry(struct dps310_data *data, s32 *value)
+	__must_hold(&data->lock)
+{
+	u8 val[3];
+	s32 raw;
+	int rc;
+
+	/* Entries come out of the pressure registers whichever made them */
+	rc = regmap_bulk_read(data->regmap, DPS310_PRS_BASE, val, sizeof(val));
+	if (rc < 0)
+		return rc;
+
+	raw = get_unaligned_be24(val);
+	if (raw == DPS310_FIFO_EMPTY_VAL)
+		return DPS310_FIFO_EMPTY;
+
+	*value = sign_extend32(raw, 23);
+
+	return raw & DPS310_FIFO_TAG_PRS ? DPS310_FIFO_PRESSURE :
+					   DPS310_FIFO_TEMP;
+}
+
+static int dps310_fifo_push_scan(struct dps310_data *data, s32 temp_raw,
+				 s32 pressure_raw)
+	__must_hold(&data->lock)
+{
+	struct iio_dev *iio = data->iio;
+	s32 channels[2] = { };
+	unsigned int i;
+	int rc;
+
+	/* Direct-mode claim keeps sysfs reads off these */
+	data->temp_raw = temp_raw;
+	data->pressure_raw = pressure_raw;
+
+	i = 0;
+	if (test_bit(DPS310_SCAN_TEMP, iio->active_scan_mask)) {
+		rc = dps310_calculate_temp(data, &channels[i++]);
+		if (rc)
+			return rc;
+	}
+
+	if (test_bit(DPS310_SCAN_PRESSURE, iio->active_scan_mask)) {
+		rc = dps310_calculate_pressure(data, &channels[i++]);
+		if (rc)
+			return rc;
+	}
+
+	iio_push_to_buffers(iio, channels);
+
+	return 0;
+}
+
+/* Pressure seen before any temperature, kept until one turns up */
+static void dps310_fifo_hold(struct dps310_data *data, s32 pressure_raw)
+	__must_hold(&data->lock)
+{
+	if (data->fifo_held < data->fifo_hold_max)
+		data->fifo_hold[data->fifo_held++] = pressure_raw;
+}
+
+/* Returns scans pushed. One that fails to compensate is dropped. */
+static unsigned int dps310_fifo_push_held(struct dps310_data *data)
+	__must_hold(&data->lock)
+{
+	unsigned int pushed = 0;
+	unsigned int i;
+
+	for (i = 0; i < data->fifo_held; i++) {
+		if (!dps310_fifo_push_scan(data, data->fifo_temp_raw,
+					   data->fifo_hold[i]))
+			pushed++;
+	}
+
+	data->fifo_held = 0;
+
+	return pushed;
+}
+
+/*
+ * Read the batch out before compensating it, so a pressure entry pairs with
+ * the temperature preceding it rather than the last one in the batch.
+ *
+ * Returns scans pushed.
+ */
+static int dps310_fifo_drain(struct dps310_data *data)
+	__must_hold(&data->lock)
+{
+	bool pressure_enabled = test_bit(DPS310_SCAN_PRESSURE,
+					 data->iio->active_scan_mask);
+	u8 kind[DPS310_FIFO_DEPTH];
+	s32 raw[DPS310_FIFO_DEPTH];
+	unsigned int pushed = 0;
+	unsigned int cnt, i;
+	int rc;
+
+	for (cnt = 0; cnt < DPS310_FIFO_DEPTH; cnt++) {
+		rc = dps310_fifo_read_entry(data, &raw[cnt]);
+		if (rc < 0)
+			return rc;
+
+		if (rc == DPS310_FIFO_EMPTY)
+			break;
+
+		kind[cnt] = rc;
+	}
+
+	for (i = 0; i < cnt; i++) {
+		if (kind[i] == DPS310_FIFO_TEMP) {
+			data->fifo_temp_raw = raw[i];
+			data->fifo_temp_valid = true;
+
+			if (pressure_enabled)
+				pushed += dps310_fifo_push_held(data);
+			else if (!dps310_fifo_push_scan(data, raw[i], 0))
+				pushed++;
+			continue;
+		}
+
+		if (!pressure_enabled)
+			continue;
+
+		if (!data->fifo_temp_valid) {
+			dps310_fifo_hold(data, raw[i]);
+			continue;
+		}
+
+		if (!dps310_fifo_push_scan(data, data->fifo_temp_raw, raw[i]))
+			pushed++;
+	}
+
+	return pushed;
+}
+
+static void dps310_fifo_work(struct work_struct *work)
+{
+	struct dps310_data *data = container_of(to_delayed_work(work),
+						struct dps310_data, fifo_work);
+	int rc;
+
+	mutex_lock(&data->lock);
+	rc = dps310_fifo_drain(data);
+	mutex_unlock(&data->lock);
+
+	if (rc < 0)
+		dev_dbg(&data->client->dev, "FIFO drain failed: %d\n", rc);
+
+	schedule_delayed_work(&data->fifo_work,
+			      msecs_to_jiffies(data->drain_interval_ms));
+}
+
+/*
+ * First temperature is one temperature period away at most, which bounds the
+ * pressure before it. Rates cannot change while the buffer runs.
+ */
+static int dps310_fifo_hold_alloc(struct dps310_data *data, int prs_rate,
+				  int tmp_rate)
+	__must_hold(&data->lock)
+{
+	data->fifo_temp_valid = false;
+	data->fifo_held = 0;
+	data->fifo_hold = NULL;
+	data->fifo_hold_max = 0;
+
+	if (!test_bit(DPS310_SCAN_PRESSURE, data->iio->active_scan_mask))
+		return 0;
+
+	data->fifo_hold_max = prs_rate / tmp_rate + 2;
+	data->fifo_hold = kcalloc(data->fifo_hold_max, sizeof(*data->fifo_hold),
+				  GFP_KERNEL);
+	if (!data->fifo_hold)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static int dps310_buffer_postenable(struct iio_dev *iio)
+{
+	struct dps310_data *data = iio_priv(iio);
+	int rc, prs_rate, tmp_rate;
+
+	/* An attached trigger drives the capture instead, FIFO stays off */
+	if (iio_device_get_current_mode(iio) == INDIO_BUFFER_TRIGGERED)
+		return 0;
+
+	/* Entries are not timestamped and the drain timer is no substitute */
+	if (iio_scan_timestamp_enabled(iio))
+		return -EINVAL;
+
+	mutex_lock(&data->lock);
+
+	rc = dps310_get_pres_samp_freq(data, &prs_rate);
+	if (rc)
+		goto err_unlock;
+
+	rc = dps310_get_temp_samp_freq(data, &tmp_rate);
+	if (rc)
+		goto err_unlock;
+
+	data->drain_interval_ms = dps310_fifo_interval(prs_rate, tmp_rate);
+
+	rc = dps310_fifo_hold_alloc(data, prs_rate, tmp_rate);
+	if (rc)
+		goto err_unlock;
+
+	/* Drop whatever accumulated before enable */
+	rc = dps310_fifo_hw_flush(data);
+	if (rc)
+		goto err_hold;
+
+	rc = dps310_fifo_set_enable(data, true);
+	if (rc)
+		goto err_hold;
+
+	schedule_delayed_work(&data->fifo_work,
+			      msecs_to_jiffies(data->drain_interval_ms));
+
+	mutex_unlock(&data->lock);
+
+	return 0;
+
+err_hold:
+	kfree(data->fifo_hold);
+err_unlock:
+	mutex_unlock(&data->lock);
+
+	return rc;
+}
+
+static int dps310_buffer_predisable(struct iio_dev *iio)
+{
+	struct dps310_data *data = iio_priv(iio);
+	int rc;
+
+	if (iio_device_get_current_mode(iio) == INDIO_BUFFER_TRIGGERED)
+		return 0;
+
+	cancel_delayed_work_sync(&data->fifo_work);
+
+	guard(mutex)(&data->lock);
+
+	kfree(data->fifo_hold);
+
+	rc = dps310_fifo_set_enable(data, false);
+	if (rc)
+		return rc;
+
+	return dps310_fifo_hw_flush(data);
+}
+
+static const struct iio_buffer_setup_ops dps310_buffer_setup_ops = {
+	.postenable = dps310_buffer_postenable,
+	.predisable = dps310_buffer_predisable,
+};
+
 static irqreturn_t dps310_trigger_handler(int irq, void *p)
 {
 	struct iio_poll_func *pf = p;
@@ -969,6 +1279,14 @@ static void dps310_reset(void *action_data)
 	dps310_reset_wait(data);
 }
 
+/* The drain rearms itself, so stop it even if the buffer never disabled */
+static void dps310_cancel_fifo_work(void *action_data)
+{
+	struct dps310_data *data = action_data;
+
+	cancel_delayed_work_sync(&data->fifo_work);
+}
+
 static const struct regmap_config dps310_regmap_config = {
 	.reg_bits = 8,
 	.val_bits = 8,
@@ -996,13 +1314,20 @@ static int dps310_probe(struct i2c_client *client)
 
 	data = iio_priv(iio);
 	data->client = client;
+	data->iio = iio;
 	mutex_init(&data->lock);
+	INIT_DELAYED_WORK(&data->fifo_work, dps310_fifo_work);
 
 	iio->name = DPS310_DEV_NAME;
 	iio->channels = dps310_channels;
 	iio->num_channels = ARRAY_SIZE(dps310_channels);
 	iio->info = &dps310_info;
-	iio->modes = INDIO_DIRECT_MODE;
+	/*
+	 * Both modes advertised: the core picks TRIGGERED with a trigger
+	 * attached and falls back to SOFTWARE, which the FIFO path uses.
+	 */
+	iio->modes = INDIO_DIRECT_MODE | INDIO_BUFFER_TRIGGERED |
+		     INDIO_BUFFER_SOFTWARE;
 
 	data->regmap = devm_regmap_init_i2c(client, &dps310_regmap_config);
 	if (IS_ERR(data->regmap))
@@ -1018,12 +1343,18 @@ static int dps310_probe(struct i2c_client *client)
 		return rc;
 
 	/*
-	 * The device measures continuously in background mode, so a capture is
-	 * just a read of the latest results. The trigger is not aligned with
-	 * the measurements, so the timestamp is taken in the handler.
+	 * The device measures continuously in background mode, so a triggered
+	 * capture is just a read of the latest results. The setup ops run the
+	 * FIFO drain when no trigger is attached. The trigger is not aligned
+	 * with the measurements, so the timestamp is taken in the handler.
 	 */
 	rc = devm_iio_triggered_buffer_setup(dev, iio, NULL,
-					     dps310_trigger_handler, NULL);
+					     dps310_trigger_handler,
+					     &dps310_buffer_setup_ops);
+	if (rc)
+		return rc;
+
+	rc = devm_add_action_or_reset(dev, dps310_cancel_fifo_work, data);
 	if (rc)
 		return rc;
 
-- 
2.43.0

Re: [PATCH v10 1/4] iio: pressure: dps310: read buffered samples from the hardware FIFO

[Andy Shevchenko]

On Wed, Sep 30, 2026 at 01:01:55PM +0300, Rupesh Majhi wrote:
> DPS310 has a 32-entry FIFO shared by both measurements. Drain it from a
> work item and push what it held, so buffered capture needs no trigger.
> Nothing in tree wires the interrupt pin, so the work rearms itself at
> half the FIFO fill time.
> 
> Each entry carries one measurement, so a pressure entry is compensated
> with the temperature ahead of it. Pressure read before a session's first
> temperature is held until one arrives rather than dropped, so the first
> push can wait a temperature period.
> 
> FIFO entries are not timestamped, so postenable refuses the timestamp
> channel unless a trigger is attached.
> 
> Tested on a DPS310 on a BeagleBone Black.

...

> +/* The drain rearms itself, so stop it even if the buffer never disabled */
> +static void dps310_cancel_fifo_work(void *action_data)
> +{
> +	struct dps310_data *data = action_data;
> +
> +	cancel_delayed_work_sync(&data->fifo_work);
> +}

...

>  	mutex_init(&data->lock);

This has to be devm_mutex_init().

...

> +	INIT_DELAYED_WORK(&data->fifo_work, dps310_fifo_work);

Can't we use devm-helpers.h for this?

...

> +	/*
> +	 * Both modes advertised: the core picks TRIGGERED with a trigger
> +	 * attached and falls back to SOFTWARE, which the FIFO path uses.
> +	 */
> +	iio->modes = INDIO_DIRECT_MODE | INDIO_BUFFER_TRIGGERED |
> +		     INDIO_BUFFER_SOFTWARE;

I would rearrange this as

	iio->modes = INDIO_BUFFER_TRIGGERED | INDIO_BUFFER_SOFTWARE |
		     INDIO_DIRECT_MODE;

...

>  	/*
> -	 * The device measures continuously in background mode, so a capture is
> -	 * just a read of the latest results. The trigger is not aligned with
> -	 * the measurements, so the timestamp is taken in the handler.
> +	 * The device measures continuously in background mode, so a triggered
> +	 * capture is just a read of the latest results. The setup ops run the
> +	 * FIFO drain when no trigger is attached. The trigger is not aligned
> +	 * with the measurements, so the timestamp is taken in the handler.
>  	 */
>  	rc = devm_iio_triggered_buffer_setup(dev, iio, NULL,
> -					     dps310_trigger_handler, NULL);
> +					     dps310_trigger_handler,
> +					     &dps310_buffer_setup_ops);
> +	if (rc)
> +		return rc;

> +	rc = devm_add_action_or_reset(dev, dps310_cancel_fifo_work, data);
>  	if (rc)
>  		return rc;

Are you sure it's in the correct location?

-- 
With Best Regards,
Andy Shevchenko

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

[Rupesh Majhi]

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

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

[Andy Shevchenko]

On Wed, Sep 30, 2026 at 01:01:56PM +0300, Rupesh Majhi wrote:
> 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.

...

> -	unsigned int fill_ms;
> +	unsigned int fill_ms, want_ms;

What about

	unsigned int drain_interval_ms, 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);

	drain_interval_ms = min(want_ms, fill_ms / 2);

	return clamp(drain_interval_ms, DPS310_DRAIN_MIN_MS, DPS310_DRAIN_MAX_MS);

?

-- 
With Best Regards,
Andy Shevchenko

[PATCH v10 3/4] iio: pressure: dps310: implement .hwfifo_flush_to_buffer()

[Rupesh Majhi]

Let userspace drain the FIFO on demand rather than only from the
periodic drain.

With a trigger attached the FIFO is not running, so there is nothing to
flush and the hook returns 0.

Hold the mode across the drain, so a concurrent buffer disable cannot
free active_scan_mask while it runs.

Assisted-by: LLM
Signed-off-by: Rupesh Majhi <zoone.rupert@gmail.com>
---
 drivers/iio/pressure/dps310.c | 36 ++++++++++++++++++++++++++++++++---
 1 file changed, 33 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/pressure/dps310.c b/drivers/iio/pressure/dps310.c
index 82bbfd097cd7..01fca139433a 100644
--- a/drivers/iio/pressure/dps310.c
+++ b/drivers/iio/pressure/dps310.c
@@ -1089,22 +1089,30 @@ static unsigned int dps310_fifo_push_held(struct dps310_data *data)
 
 /*
  * Read the batch out before compensating it, so a pressure entry pairs with
- * the temperature preceding it rather than the last one in the batch.
+ * the temperature preceding it rather than the last one in the batch. Stop
+ * reading at max_scans rather than after it, since entries leave the hardware
+ * as they are read and any extra would have to be thrown away. max_scans of
+ * zero drains everything.
  *
  * Returns scans pushed.
  */
-static int dps310_fifo_drain(struct dps310_data *data)
+static int dps310_fifo_drain(struct dps310_data *data, unsigned int max_scans)
 	__must_hold(&data->lock)
 {
 	bool pressure_enabled = test_bit(DPS310_SCAN_PRESSURE,
 					 data->iio->active_scan_mask);
 	u8 kind[DPS310_FIFO_DEPTH];
 	s32 raw[DPS310_FIFO_DEPTH];
+	unsigned int scans = 0;
 	unsigned int pushed = 0;
 	unsigned int cnt, i;
+	bool is_pressure;
 	int rc;
 
 	for (cnt = 0; cnt < DPS310_FIFO_DEPTH; cnt++) {
+		if (max_scans && scans >= max_scans)
+			break;
+
 		rc = dps310_fifo_read_entry(data, &raw[cnt]);
 		if (rc < 0)
 			return rc;
@@ -1112,7 +1120,12 @@ static int dps310_fifo_drain(struct dps310_data *data)
 		if (rc == DPS310_FIFO_EMPTY)
 			break;
 
+		is_pressure = rc == DPS310_FIFO_PRESSURE;
 		kind[cnt] = rc;
+
+		/* Only the measurement that drives the scans counts */
+		if (is_pressure == pressure_enabled)
+			scans++;
 	}
 
 	for (i = 0; i < cnt; i++) {
@@ -1149,7 +1162,7 @@ static void dps310_fifo_work(struct work_struct *work)
 	int rc;
 
 	mutex_lock(&data->lock);
-	rc = dps310_fifo_drain(data);
+	rc = dps310_fifo_drain(data, 0);
 	mutex_unlock(&data->lock);
 
 	if (rc < 0)
@@ -1184,6 +1197,22 @@ static int dps310_fifo_hold_alloc(struct dps310_data *data, int prs_rate,
 	return 0;
 }
 
+static int dps310_hwfifo_flush(struct iio_dev *iio, unsigned int count)
+{
+	struct dps310_data *data = iio_priv(iio);
+
+	/* Holding the mode keeps active_scan_mask alive across the drain */
+	IIO_DEV_GUARD_CURRENT_MODE(iio);
+
+	/* A trigger drives the capture instead and leaves the FIFO empty */
+	if (iio_device_get_current_mode(iio) != INDIO_BUFFER_SOFTWARE)
+		return 0;
+
+	guard(mutex)(&data->lock);
+
+	return dps310_fifo_drain(data, count);
+}
+
 static int dps310_hwfifo_set_watermark(struct iio_dev *iio, unsigned int val)
 {
 	struct dps310_data *data = iio_priv(iio);
@@ -1325,6 +1354,7 @@ static const struct iio_info dps310_info = {
 	.read_raw = dps310_read_raw,
 	.write_raw = dps310_write_raw,
 	.hwfifo_set_watermark = dps310_hwfifo_set_watermark,
+	.hwfifo_flush_to_buffer = dps310_hwfifo_flush,
 };
 
 static int dps310_probe(struct i2c_client *client)
-- 
2.43.0

[PATCH v10 4/4] iio: pressure: dps310: assert the lock at runtime too

[Rupesh Majhi]

__must_hold() is clang only and does nothing in GCC builds. Add
lockdep_assert_held() next to each, so lockdep catches a missing lock
too.

Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Assisted-by: LLM
Signed-off-by: Rupesh Majhi <zoone.rupert@gmail.com>
---
 drivers/iio/pressure/dps310.c | 41 +++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/drivers/iio/pressure/dps310.c b/drivers/iio/pressure/dps310.c
index 01fca139433a..791ff22b0304 100644
--- a/drivers/iio/pressure/dps310.c
+++ b/drivers/iio/pressure/dps310.c
@@ -12,6 +12,7 @@
 #include <linux/cleanup.h>
 #include <linux/i2c.h>
 #include <linux/limits.h>
+#include <linux/lockdep.h>
 #include <linux/math64.h>
 #include <linux/module.h>
 #include <linux/regmap.h>
@@ -358,6 +359,8 @@ static int dps310_set_pres_precision(struct dps310_data *data, int val)
 	int rc;
 	u8 shift_en;
 
+	lockdep_assert_held(&data->lock);
+
 	if (val < 0 || val > 128)
 		return -EINVAL;
 
@@ -377,6 +380,8 @@ static int dps310_set_temp_precision(struct dps310_data *data, int val)
 	int rc;
 	u8 shift_en;
 
+	lockdep_assert_held(&data->lock);
+
 	if (val < 0 || val > 128)
 		return -EINVAL;
 
@@ -395,6 +400,8 @@ static int dps310_set_pres_samp_freq(struct dps310_data *data, int freq)
 {
 	u8 val;
 
+	lockdep_assert_held(&data->lock);
+
 	if (freq < 0 || freq > 128)
 		return -EINVAL;
 
@@ -409,6 +416,8 @@ static int dps310_set_temp_samp_freq(struct dps310_data *data, int freq)
 {
 	u8 val;
 
+	lockdep_assert_held(&data->lock);
+
 	if (freq < 0 || freq > 128)
 		return -EINVAL;
 
@@ -508,6 +517,8 @@ static int dps310_ready(struct dps310_data *data, int ready_bit, int timeout)
 {
 	int rc;
 
+	lockdep_assert_held(&data->lock);
+
 	rc = dps310_ready_status(data, ready_bit, timeout);
 	if (rc) {
 		if (rc == -ETIMEDOUT && !data->timeout_recovery_failed) {
@@ -538,6 +549,8 @@ static int dps310_read_pres_raw_locked(struct dps310_data *data)
 	int timeout;
 	u8 val[3];
 
+	lockdep_assert_held(&data->lock);
+
 	rc = dps310_get_pres_samp_freq(data, &rate);
 	if (rc)
 		return rc;
@@ -564,6 +577,8 @@ static int dps310_read_temp_ready(struct dps310_data *data)
 	int rc;
 	u8 val[3];
 
+	lockdep_assert_held(&data->lock);
+
 	rc = regmap_bulk_read(data->regmap, DPS310_TMP_BASE, val, sizeof(val));
 	if (rc < 0)
 		return rc;
@@ -580,6 +595,8 @@ static int dps310_read_temp_raw_locked(struct dps310_data *data)
 	int rate;
 	int timeout;
 
+	lockdep_assert_held(&data->lock);
+
 	rc = dps310_get_temp_samp_freq(data, &rate);
 	if (rc)
 		return rc;
@@ -601,6 +618,8 @@ static void dps310_refresh_temp_locked(struct dps310_data *data)
 	int rc;
 	int t_ready;
 
+	lockdep_assert_held(&data->lock);
+
 	rc = regmap_read(data->regmap, DPS310_MEAS_CFG, &t_ready);
 	if (rc)
 		return;
@@ -706,6 +725,8 @@ static int dps310_calculate_pressure(struct dps310_data *data, int *val)
 	s64 kp;
 	s64 kt;
 
+	lockdep_assert_held(&data->lock);
+
 	rc = dps310_get_pres_k(data, &kpi);
 	if (rc)
 		return rc;
@@ -831,6 +852,8 @@ static int dps310_calculate_temp(struct dps310_data *data, int *val)
 	s64 t;
 	int kt, rc;
 
+	lockdep_assert_held(&data->lock);
+
 	rc = dps310_get_temp_k(data, &kt);
 	if (rc)
 		return rc;
@@ -939,6 +962,8 @@ static int dps310_fill_channels(struct dps310_data *data,
 	unsigned int i;
 	int rc;
 
+	lockdep_assert_held(&data->lock);
+
 	/* Compensation needs a temperature, so it is sampled either way */
 	rc = dps310_read_temp_raw_locked(data);
 	if (rc)
@@ -969,12 +994,16 @@ static int dps310_fill_channels(struct dps310_data *data,
 static int dps310_fifo_hw_flush(struct dps310_data *data)
 	__must_hold(&data->lock)
 {
+	lockdep_assert_held(&data->lock);
+
 	return regmap_write(data->regmap, DPS310_RESET, DPS310_FIFO_FLUSH);
 }
 
 static int dps310_fifo_set_enable(struct dps310_data *data, bool enable)
 	__must_hold(&data->lock)
 {
+	lockdep_assert_held(&data->lock);
+
 	return regmap_assign_bits(data->regmap, DPS310_CFG_REG, DPS310_FIFO_EN,
 				  enable);
 }
@@ -1015,6 +1044,8 @@ static int dps310_fifo_read_entry(struct dps310_data *data, s32 *value)
 	s32 raw;
 	int rc;
 
+	lockdep_assert_held(&data->lock);
+
 	/* Entries come out of the pressure registers whichever made them */
 	rc = regmap_bulk_read(data->regmap, DPS310_PRS_BASE, val, sizeof(val));
 	if (rc < 0)
@@ -1039,6 +1070,8 @@ static int dps310_fifo_push_scan(struct dps310_data *data, s32 temp_raw,
 	unsigned int i;
 	int rc;
 
+	lockdep_assert_held(&data->lock);
+
 	/* Direct-mode claim keeps sysfs reads off these */
 	data->temp_raw = temp_raw;
 	data->pressure_raw = pressure_raw;
@@ -1065,6 +1098,8 @@ static int dps310_fifo_push_scan(struct dps310_data *data, s32 temp_raw,
 static void dps310_fifo_hold(struct dps310_data *data, s32 pressure_raw)
 	__must_hold(&data->lock)
 {
+	lockdep_assert_held(&data->lock);
+
 	if (data->fifo_held < data->fifo_hold_max)
 		data->fifo_hold[data->fifo_held++] = pressure_raw;
 }
@@ -1076,6 +1111,8 @@ static unsigned int dps310_fifo_push_held(struct dps310_data *data)
 	unsigned int pushed = 0;
 	unsigned int i;
 
+	lockdep_assert_held(&data->lock);
+
 	for (i = 0; i < data->fifo_held; i++) {
 		if (!dps310_fifo_push_scan(data, data->fifo_temp_raw,
 					   data->fifo_hold[i]))
@@ -1109,6 +1146,8 @@ static int dps310_fifo_drain(struct dps310_data *data, unsigned int max_scans)
 	bool is_pressure;
 	int rc;
 
+	lockdep_assert_held(&data->lock);
+
 	for (cnt = 0; cnt < DPS310_FIFO_DEPTH; cnt++) {
 		if (max_scans && scans >= max_scans)
 			break;
@@ -1180,6 +1219,8 @@ static int dps310_fifo_hold_alloc(struct dps310_data *data, int prs_rate,
 				  int tmp_rate)
 	__must_hold(&data->lock)
 {
+	lockdep_assert_held(&data->lock);
+
 	data->fifo_temp_valid = false;
 	data->fifo_held = 0;
 	data->fifo_hold = NULL;
-- 
2.43.0

Re: [PATCH v10 4/4] iio: pressure: dps310: assert the lock at runtime too

[Andy Shevchenko]

On Wed, Sep 30, 2026 at 01:01:58PM +0300, Rupesh Majhi wrote:
> __must_hold() is clang only and does nothing in GCC builds. Add
> lockdep_assert_held() next to each, so lockdep catches a missing lock
> too.

> Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>

Not really, I just explained the difference and asked if lockdep annotations
would be also good to have. Otherwise if Jonathan thinks it's fine, I have
no objections (and also have no objections on not taking this change).

-- 
With Best Regards,
Andy Shevchenko