[PATCH v2 0/3] iio: common: improve InvenSense sample timestamping

[PATCH v2 0/3] iio: common: improve InvenSense sample timestamping

[Jean-Baptiste Maneyrol via B4 Relay]

This series improves the InvenSense timestamping mechanism for 2 cases:
when using watermark and for high frequency sampling.

Data arriving by batch because of FIFO watermark will now be all aligned
correctly with the interrupt timestamp and the chip period measurement
will use a minimal period of 20ms to ensure that system latency is
not preventing measurement when using high frequency sampling.

This was tested using inv_icm42600 driver when using maximum FIFO
watermark and when using 1kHz sampling frequency.

Signed-off-by: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>
---
Changes in v2:
- Add a 1st patch to convert to kernel types.
- Rework following review suggestions.
- Following Sashiko fix delta_counter usage and handle case of
  timestamp overflowing last interrupt by using s64 type for new_period.
- Reword commit message for better timestamp alignement using Jonathan
  proposition.
- Link to v1: https://patch.msgid.link/20260717-iio-common-inv-sensors-timestamp-rework-v1-0-d1afee2805cd@tdk.com

To: Jonathan Cameron <jic23@kernel.org>
To: David Lechner <dlechner@baylibre.com>
To: Nuno Sá <nuno.sa@analog.com>
To: Andy Shevchenko <andy@kernel.org>
Cc: linux-iio@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

---
Jean-Baptiste Maneyrol (3):
      iio: inv_sensors: convert to kernel types
      iio: inv_sensors: better timestamp alignment when using watermark
      iio: inv_sensors: improve period measurement by using a longer delay

 .../iio/common/inv_sensors/inv_sensors_timestamp.c | 109 +++++++++++----------
 include/linux/iio/common/inv_sensors_timestamp.h   |  40 ++++----
 2 files changed, 81 insertions(+), 68 deletions(-)
---
base-commit: aa58ecc73466d0cb8c418de98e2225490bf600e3
change-id: 20260715-iio-common-inv-sensors-timestamp-rework-acf1a0aa00f4

Best regards,
--  
Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>

[PATCH v2 1/3] iio: inv_sensors: convert to kernel types

[Jean-Baptiste Maneyrol via B4 Relay]

From: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>

Convert standard types (u)intXX_t to kernel type u/sXX.

Signed-off-by: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>
---
 .../iio/common/inv_sensors/inv_sensors_timestamp.c | 48 +++++++++++-----------
 include/linux/iio/common/inv_sensors_timestamp.h   | 34 +++++++--------
 2 files changed, 41 insertions(+), 41 deletions(-)

diff --git a/drivers/iio/common/inv_sensors/inv_sensors_timestamp.c b/drivers/iio/common/inv_sensors/inv_sensors_timestamp.c
index e0b10366ed2b..ecfd54ffe7e9 100644
--- a/drivers/iio/common/inv_sensors/inv_sensors_timestamp.c
+++ b/drivers/iio/common/inv_sensors/inv_sensors_timestamp.c
@@ -19,9 +19,9 @@
 	(((_val) * (1000 + (_jitter))) / 1000)
 
 /* Add a new value inside an accumulator and update the estimate value */
-static void inv_update_acc(struct inv_sensors_timestamp_acc *acc, uint32_t val)
+static void inv_update_acc(struct inv_sensors_timestamp_acc *acc, u32 val)
 {
-	uint64_t sum = 0;
+	u64 sum = 0;
 	size_t i;
 
 	acc->values[acc->idx++] = val;
@@ -58,9 +58,9 @@ void inv_sensors_timestamp_init(struct inv_sensors_timestamp *ts,
 EXPORT_SYMBOL_NS_GPL(inv_sensors_timestamp_init, "IIO_INV_SENSORS_TIMESTAMP");
 
 int inv_sensors_timestamp_update_odr(struct inv_sensors_timestamp *ts,
-				     uint32_t period, bool fifo)
+				     u32 period, bool fifo)
 {
-	uint32_t mult;
+	u32 mult;
 
 	/* when FIFO is on, prevent odr change if one is already pending */
 	if (fifo && ts->new_mult != 0)
@@ -78,9 +78,9 @@ int inv_sensors_timestamp_update_odr(struct inv_sensors_timestamp *ts,
 }
 EXPORT_SYMBOL_NS_GPL(inv_sensors_timestamp_update_odr, "IIO_INV_SENSORS_TIMESTAMP");
 
-static bool inv_validate_period(struct inv_sensors_timestamp *ts, uint32_t period)
+static bool inv_validate_period(struct inv_sensors_timestamp *ts, u32 period)
 {
-	uint32_t period_min, period_max;
+	u32 period_min, period_max;
 
 	/* check that period is acceptable */
 	period_min = ts->min_period * ts->mult;
@@ -92,9 +92,9 @@ static bool inv_validate_period(struct inv_sensors_timestamp *ts, uint32_t perio
 }
 
 static bool inv_update_chip_period(struct inv_sensors_timestamp *ts,
-				   uint32_t period)
+				   u32 period)
 {
-	uint32_t new_chip_period;
+	u32 new_chip_period;
 
 	if (!inv_validate_period(ts, period))
 		return false;
@@ -109,19 +109,19 @@ static bool inv_update_chip_period(struct inv_sensors_timestamp *ts,
 
 static void inv_align_timestamp_it(struct inv_sensors_timestamp *ts)
 {
-	const int64_t period_min = (int64_t)ts->min_period * ts->mult;
-	const int64_t period_max = (int64_t)ts->max_period * ts->mult;
-	int64_t add_max, sub_max;
-	int64_t delta, jitter;
-	int64_t adjust;
+	const s64 period_min = (s64)ts->min_period * ts->mult;
+	const s64 period_max = (s64)ts->max_period * ts->mult;
+	s64 add_max, sub_max;
+	s64 delta, jitter;
+	s64 adjust;
 
 	/* delta time between last sample and last interrupt */
 	delta = ts->it.lo - ts->timestamp;
 
 	/* adjust timestamp while respecting jitter */
-	add_max = period_max - (int64_t)ts->period;
-	sub_max = period_min - (int64_t)ts->period;
-	jitter = INV_SENSORS_TIMESTAMP_JITTER((int64_t)ts->period, ts->chip.jitter);
+	add_max = period_max - (s64)ts->period;
+	sub_max = period_min - (s64)ts->period;
+	jitter = INV_SENSORS_TIMESTAMP_JITTER((s64)ts->period, ts->chip.jitter);
 	if (delta > jitter)
 		adjust = add_max;
 	else if (delta < -jitter)
@@ -133,11 +133,11 @@ static void inv_align_timestamp_it(struct inv_sensors_timestamp *ts)
 }
 
 void inv_sensors_timestamp_interrupt(struct inv_sensors_timestamp *ts,
-				     size_t sample_nb, int64_t timestamp)
+				     size_t sample_nb, s64 timestamp)
 {
 	struct inv_sensors_timestamp_interval *it;
-	int64_t delta, interval;
-	uint32_t period;
+	s64 delta, interval;
+	u32 period;
 	bool valid = false;
 
 	if (sample_nb == 0)
@@ -157,7 +157,7 @@ void inv_sensors_timestamp_interrupt(struct inv_sensors_timestamp *ts,
 	/* no previous data, compute theoretical value from interrupt */
 	if (ts->timestamp == 0) {
 		/* elapsed time: sensor period * sensor samples number */
-		interval = (int64_t)ts->period * (int64_t)sample_nb;
+		interval = (s64)ts->period * (s64)sample_nb;
 		ts->timestamp = it->up - interval;
 		return;
 	}
@@ -169,11 +169,11 @@ void inv_sensors_timestamp_interrupt(struct inv_sensors_timestamp *ts,
 EXPORT_SYMBOL_NS_GPL(inv_sensors_timestamp_interrupt, "IIO_INV_SENSORS_TIMESTAMP");
 
 void inv_sensors_timestamp_apply_odr(struct inv_sensors_timestamp *ts,
-				     uint32_t fifo_period, size_t fifo_nb,
+				     u32 fifo_period, size_t fifo_nb,
 				     unsigned int fifo_no)
 {
-	int64_t interval;
-	uint32_t fifo_mult;
+	s64 interval;
+	u32 fifo_mult;
 
 	if (ts->new_mult == 0)
 		return;
@@ -194,7 +194,7 @@ void inv_sensors_timestamp_apply_odr(struct inv_sensors_timestamp *ts,
 		fifo_mult = fifo_period / ts->chip.clock_period;
 		fifo_period = fifo_mult * ts->chip_period.val;
 		/* computes time interval between interrupt and this sample */
-		interval = (int64_t)(fifo_nb - fifo_no) * (int64_t)fifo_period;
+		interval = (s64)(fifo_nb - fifo_no) * (s64)fifo_period;
 		ts->timestamp = ts->it.up - interval;
 	}
 }
diff --git a/include/linux/iio/common/inv_sensors_timestamp.h b/include/linux/iio/common/inv_sensors_timestamp.h
index 8d506f1e9df2..e4e720e6f4b7 100644
--- a/include/linux/iio/common/inv_sensors_timestamp.h
+++ b/include/linux/iio/common/inv_sensors_timestamp.h
@@ -13,9 +13,9 @@
  * @init_period:	chip initial period at reset in ns
  */
 struct inv_sensors_timestamp_chip {
-	uint32_t clock_period;
-	uint32_t jitter;
-	uint32_t init_period;
+	u32 clock_period;
+	u32 jitter;
+	u32 init_period;
 };
 
 /**
@@ -24,8 +24,8 @@ struct inv_sensors_timestamp_chip {
  * @up:	interval upper bound
  */
 struct inv_sensors_timestamp_interval {
-	int64_t lo;
-	int64_t up;
+	s64 lo;
+	s64 up;
 };
 
 /**
@@ -35,9 +35,9 @@ struct inv_sensors_timestamp_interval {
  * @values:	table of all measured values, use for computing the mean
  */
 struct inv_sensors_timestamp_acc {
-	uint32_t val;
+	u32 val;
 	size_t idx;
-	uint32_t values[32];
+	u32 values[32];
 };
 
 /**
@@ -54,13 +54,13 @@ struct inv_sensors_timestamp_acc {
  */
 struct inv_sensors_timestamp {
 	struct inv_sensors_timestamp_chip chip;
-	uint32_t min_period;
-	uint32_t max_period;
+	u32 min_period;
+	u32 max_period;
 	struct inv_sensors_timestamp_interval it;
-	int64_t timestamp;
-	uint32_t mult;
-	uint32_t new_mult;
-	uint32_t period;
+	s64 timestamp;
+	u32 mult;
+	u32 new_mult;
+	u32 period;
 	struct inv_sensors_timestamp_acc chip_period;
 };
 
@@ -68,19 +68,19 @@ void inv_sensors_timestamp_init(struct inv_sensors_timestamp *ts,
 				const struct inv_sensors_timestamp_chip *chip);
 
 int inv_sensors_timestamp_update_odr(struct inv_sensors_timestamp *ts,
-				     uint32_t period, bool fifo);
+				     u32 period, bool fifo);
 
 void inv_sensors_timestamp_interrupt(struct inv_sensors_timestamp *ts,
-				     size_t sample_nb, int64_t timestamp);
+				     size_t sample_nb, s64 timestamp);
 
-static inline int64_t inv_sensors_timestamp_pop(struct inv_sensors_timestamp *ts)
+static inline s64 inv_sensors_timestamp_pop(struct inv_sensors_timestamp *ts)
 {
 	ts->timestamp += ts->period;
 	return ts->timestamp;
 }
 
 void inv_sensors_timestamp_apply_odr(struct inv_sensors_timestamp *ts,
-				     uint32_t fifo_period, size_t fifo_nb,
+				     u32 fifo_period, size_t fifo_nb,
 				     unsigned int fifo_no);
 
 static inline void inv_sensors_timestamp_reset(struct inv_sensors_timestamp *ts)

-- 
2.54.0

Re: [PATCH v2 1/3] iio: inv_sensors: convert to kernel types

[Andy Shevchenko]

On Mon, Jul 20, 2026 at 12:38:32PM +0200, Jean-Baptiste Maneyrol via B4 Relay wrote:

> Convert standard types (u)intXX_t to kernel type u/sXX.

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

...

>  void inv_sensors_timestamp_apply_odr(struct inv_sensors_timestamp *ts,
> -				     uint32_t fifo_period, size_t fifo_nb,
> +				     u32 fifo_period, size_t fifo_nb,
>  				     unsigned int fifo_no)
>  {
> -	int64_t interval;
> -	uint32_t fifo_mult;
> +	s64 interval;
> +	u32 fifo_mult;

It makes sense to also amend the ordering to follow reversed xmas tree.
(On a glance there are more places, but let Jonathan to tweak if he feels
 so.)

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v2 1/3] iio: inv_sensors: convert to kernel types

[Jonathan Cameron]

On Mon, 20 Jul 2026 14:29:53 +0300
Andy Shevchenko <andriy.shevchenko@intel.com> wrote:

> On Mon, Jul 20, 2026 at 12:38:32PM +0200, Jean-Baptiste Maneyrol via B4 Relay wrote:
> 
> > Convert standard types (u)intXX_t to kernel type u/sXX.  
> 
> Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
> 
> ...
> 
> >  void inv_sensors_timestamp_apply_odr(struct inv_sensors_timestamp *ts,
> > -				     uint32_t fifo_period, size_t fifo_nb,
> > +				     u32 fifo_period, size_t fifo_nb,
> >  				     unsigned int fifo_no)
> >  {
> > -	int64_t interval;
> > -	uint32_t fifo_mult;
> > +	s64 interval;
> > +	u32 fifo_mult;  
> 
> It makes sense to also amend the ordering to follow reversed xmas tree.
> (On a glance there are more places, but let Jonathan to tweak if he feels
>  so.)
> 
I'm feeling lazy so nope, left them alone.

Picked up the series on the testing branch of iio.git.

Thanks,

Jonathan

[PATCH v2 2/3] iio: inv_sensors: better timestamp alignment when using watermark

[Jean-Baptiste Maneyrol via B4 Relay]

From: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>

Current interrupt timestamp alignment only changes the final timestamp.
When the watermark is in use, we have a batch of samples for each
interrupt. The current code doesn't manage to align the timestamp
because the jitter is too high.

Instead modify the estimated inter interrupt period and use that to
adjust the timestamp alignment over the batch in a linear fashion.

Signed-off-by: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>
---
 .../iio/common/inv_sensors/inv_sensors_timestamp.c | 51 ++++++++--------------
 1 file changed, 19 insertions(+), 32 deletions(-)

diff --git a/drivers/iio/common/inv_sensors/inv_sensors_timestamp.c b/drivers/iio/common/inv_sensors/inv_sensors_timestamp.c
index ecfd54ffe7e9..2aaaa8df6d03 100644
--- a/drivers/iio/common/inv_sensors/inv_sensors_timestamp.c
+++ b/drivers/iio/common/inv_sensors/inv_sensors_timestamp.c
@@ -10,9 +10,7 @@
 
 #include <linux/iio/common/inv_sensors_timestamp.h>
 
-/* compute jitter, min and max following jitter in per mille */
-#define INV_SENSORS_TIMESTAMP_JITTER(_val, _jitter)		\
-	(div_s64((_val) * (_jitter), 1000))
+/* compute min and max following jitter in per mille */
 #define INV_SENSORS_TIMESTAMP_MIN(_val, _jitter)		\
 	(((_val) * (1000 - (_jitter))) / 1000)
 #define INV_SENSORS_TIMESTAMP_MAX(_val, _jitter)		\
@@ -102,34 +100,22 @@ static bool inv_update_chip_period(struct inv_sensors_timestamp *ts,
 	/* update chip internal period estimation */
 	new_chip_period = period / ts->mult;
 	inv_update_acc(&ts->chip_period, new_chip_period);
-	ts->period = ts->mult * ts->chip_period.val;
 
 	return true;
 }
 
-static void inv_align_timestamp_it(struct inv_sensors_timestamp *ts)
+static u32 inv_align_timestamp_it(struct inv_sensors_timestamp *ts,
+				  unsigned int sample_nb)
 {
 	const s64 period_min = (s64)ts->min_period * ts->mult;
 	const s64 period_max = (s64)ts->max_period * ts->mult;
-	s64 add_max, sub_max;
-	s64 delta, jitter;
-	s64 adjust;
-
-	/* delta time between last sample and last interrupt */
-	delta = ts->it.lo - ts->timestamp;
-
-	/* adjust timestamp while respecting jitter */
-	add_max = period_max - (s64)ts->period;
-	sub_max = period_min - (s64)ts->period;
-	jitter = INV_SENSORS_TIMESTAMP_JITTER((s64)ts->period, ts->chip.jitter);
-	if (delta > jitter)
-		adjust = add_max;
-	else if (delta < -jitter)
-		adjust = sub_max;
-	else
-		adjust = 0;
+	s64 new_period;
+
+	/* compute new period aligning last timestamp with interrupt timestamp */
+	new_period = div_s64(ts->it.up - ts->timestamp, sample_nb);
 
-	ts->timestamp += adjust;
+	/* ensure that period never overflows the jitter */
+	return clamp(new_period, period_min, period_max);
 }
 
 void inv_sensors_timestamp_interrupt(struct inv_sensors_timestamp *ts,
@@ -143,6 +129,13 @@ void inv_sensors_timestamp_interrupt(struct inv_sensors_timestamp *ts,
 	if (sample_nb == 0)
 		return;
 
+	/* no previous data, compute theoretical value from interrupt */
+	if (ts->timestamp == 0) {
+		/* elapsed time: sensor period * sensor samples number */
+		interval = (s64)ts->period * (s64)sample_nb;
+		ts->timestamp = timestamp - interval;
+	}
+
 	/* update interrupt timestamp and compute chip and sensor periods */
 	it = &ts->it;
 	it->lo = it->up;
@@ -154,17 +147,11 @@ void inv_sensors_timestamp_interrupt(struct inv_sensors_timestamp *ts,
 		valid = inv_update_chip_period(ts, period);
 	}
 
-	/* no previous data, compute theoretical value from interrupt */
-	if (ts->timestamp == 0) {
-		/* elapsed time: sensor period * sensor samples number */
-		interval = (s64)ts->period * (s64)sample_nb;
-		ts->timestamp = it->up - interval;
-		return;
-	}
-
 	/* if interrupt interval is valid, sync with interrupt timestamp */
 	if (valid)
-		inv_align_timestamp_it(ts);
+		ts->period = inv_align_timestamp_it(ts, sample_nb);
+	else
+		ts->period = ts->mult * ts->chip_period.val;
 }
 EXPORT_SYMBOL_NS_GPL(inv_sensors_timestamp_interrupt, "IIO_INV_SENSORS_TIMESTAMP");
 

-- 
2.54.0

Re: [PATCH v2 2/3] iio: inv_sensors: better timestamp alignment when using watermark

[Andy Shevchenko]

On Mon, Jul 20, 2026 at 12:38:33PM +0200, Jean-Baptiste Maneyrol via B4 Relay wrote:

> Current interrupt timestamp alignment only changes the final timestamp.
> When the watermark is in use, we have a batch of samples for each
> interrupt. The current code doesn't manage to align the timestamp
> because the jitter is too high.
> 
> Instead modify the estimated inter interrupt period and use that to
> adjust the timestamp alignment over the batch in a linear fashion.

...

>  void inv_sensors_timestamp_interrupt(struct inv_sensors_timestamp *ts,

>  	if (sample_nb == 0)
>  		return;
>  
> +	/* no previous data, compute theoretical value from interrupt */
> +	if (ts->timestamp == 0) {
> +		/* elapsed time: sensor period * sensor samples number */
> +		interval = (s64)ts->period * (s64)sample_nb;

The both variables are unsigned. Why do we cast them to the signed type?

> +		ts->timestamp = timestamp - interval;
> +	}

...

> -	/* no previous data, compute theoretical value from interrupt */
> -	if (ts->timestamp == 0) {
> -		/* elapsed time: sensor period * sensor samples number */
> -		interval = (s64)ts->period * (s64)sample_nb;

Yeah, I see this is the original code, but consider revisiting.

> -		ts->timestamp = it->up - interval;
> -		return;
> -	}

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v2 2/3] iio: inv_sensors: better timestamp alignment when using watermark

[Jean-Baptiste Maneyrol]

>________________________________________
>From: Andy Shevchenko <andriy.shevchenko@intel.com>
>Sent: Monday, July 20, 2026 13:33
>To: Jean-Baptiste Maneyrol
>Cc: Jonathan Cameron; David Lechner; Nuno Sá; Andy Shevchenko; linux-iio@vger.kernel.org; linux-kernel@vger.kernel.org
>Subject: Re: [PATCH v2 2/3] iio: inv_sensors: better timestamp alignment when using watermark
>
>On Mon, Jul 20, 2026 at 12: 38: 33PM +0200, Jean-Baptiste Maneyrol via B4 Relay wrote: > Current interrupt timestamp alignment only changes the final timestamp. > When the watermark is in use, we have a batch of samples for each > interrupt. 
>ZjQcmQRYFpfptBannerStart
>This Message Is From an External Sender
>This message came from outside your organization.
>
>ZjQcmQRYFpfptBannerEnd
>
>On Mon, Jul 20, 2026 at 12:38:33PM +0200, Jean-Baptiste Maneyrol via B4 Relay wrote:
>
>> Current interrupt timestamp alignment only changes the final timestamp.
>> When the watermark is in use, we have a batch of samples for each
>> interrupt. The current code doesn't manage to align the timestamp
>> because the jitter is too high.
>>
>> Instead modify the estimated inter interrupt period and use that to
>> adjust the timestamp alignment over the batch in a linear fashion.
>
>...
>
>>  void inv_sensors_timestamp_interrupt(struct inv_sensors_timestamp *ts,
>
>>       if (sample_nb == 0)
>>               return;
>>
>> +     /* no previous data, compute theoretical value from interrupt */
>> +     if (ts->timestamp == 0) {
>> +             /* elapsed time: sensor period * sensor samples number */
>> +             interval = (s64)ts->period * (s64)sample_nb;
>
>The both variables are unsigned. Why do we cast them to the signed type?
>
Hello Andy,

the idea here is to have a (timestamp - interval) doing the difference on
variables of the same type, s64. I tried to avoid difference between signed
and unsigned values that can be problematic.

Interval is s64 for this reason, and that's why I cast the 2 u32 values to
s64 (which should not be a problem).

Is that OK like this or do you prefer I change to u64 (with implicit
conversion to s64 when assigning to interval)?

>> +             ts->timestamp = timestamp - interval;
>> +     }
>
>...
>
>> -     /* no previous data, compute theoretical value from interrupt */
>> -     if (ts->timestamp == 0) {
>> -             /* elapsed time: sensor period * sensor samples number */
>> -             interval = (s64)ts->period * (s64)sample_nb;
>
>Yeah, I see this is the original code, but consider revisiting.
>
>> -             ts->timestamp = it->up - interval;
>> -             return;
>> -     }
>
>--
>With Best Regards,
>Andy Shevchenko
>

Thanks,
JB

Re: [PATCH v2 2/3] iio: inv_sensors: better timestamp alignment when using watermark

[Andy Shevchenko]

On Mon, Jul 20, 2026 at 03:07:05PM +0000, Jean-Baptiste Maneyrol wrote:
> >________________________________________
> >From: Andy Shevchenko <andriy.shevchenko@intel.com>
> >Sent: Monday, July 20, 2026 13:33
> >On Mon, Jul 20, 2026 at 12:38:33PM +0200, Jean-Baptiste Maneyrol via B4 Relay wrote:

...

> >>  void inv_sensors_timestamp_interrupt(struct inv_sensors_timestamp *ts,
> >
> >>       if (sample_nb == 0)
> >>               return;
> >>
> >> +     /* no previous data, compute theoretical value from interrupt */
> >> +     if (ts->timestamp == 0) {
> >> +             /* elapsed time: sensor period * sensor samples number */
> >> +             interval = (s64)ts->period * (s64)sample_nb;
> >
> >The both variables are unsigned. Why do we cast them to the signed type?
> >
> Hello Andy,
> 
> the idea here is to have a (timestamp - interval) doing the difference on
> variables of the same type, s64. I tried to avoid difference between signed
> and unsigned values that can be problematic.
> 
> Interval is s64 for this reason, and that's why I cast the 2 u32 values to
> s64 (which should not be a problem).
> 
> Is that OK like this or do you prefer I change to u64 (with implicit
> conversion to s64 when assigning to interval)?

It was just a question. If you think it's better as is, I'm fine.

> >> +             ts->timestamp = timestamp - interval;
> >> +     }

...

> >> -     /* no previous data, compute theoretical value from interrupt */
> >> -     if (ts->timestamp == 0) {
> >> -             /* elapsed time: sensor period * sensor samples number */
> >> -             interval = (s64)ts->period * (s64)sample_nb;
> >
> >Yeah, I see this is the original code, but consider revisiting.
> >
> >> -             ts->timestamp = it->up - interval;
> >> -             return;
> >> -     }

-- 
With Best Regards,
Andy Shevchenko

[PATCH v2 3/3] iio: inv_sensors: improve period measurement by using a longer delay

[Jean-Baptiste Maneyrol via B4 Relay]

From: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>

Period measurement can be difficult when using high sampling
frequency where the jitter criteria is hard to meet because of the
system jitter.

This new version is using the delta time between 2 distant interrupts
to measure an interval of at least 20ms. 20ms is a good compromise
between the mitigation of system jitter and the delay to update
period. This way we decorrelate the period measurement from the
interrupt timestamps syncing using only the 2 last interrupts.

Signed-off-by: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>
---
 .../iio/common/inv_sensors/inv_sensors_timestamp.c | 26 +++++++++++++++++++---
 include/linux/iio/common/inv_sensors_timestamp.h   |  6 +++++
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/common/inv_sensors/inv_sensors_timestamp.c b/drivers/iio/common/inv_sensors/inv_sensors_timestamp.c
index 2aaaa8df6d03..88a82d1370c5 100644
--- a/drivers/iio/common/inv_sensors/inv_sensors_timestamp.c
+++ b/drivers/iio/common/inv_sensors/inv_sensors_timestamp.c
@@ -16,6 +16,9 @@
 #define INV_SENSORS_TIMESTAMP_MAX(_val, _jitter)		\
 	(((_val) * (1000 + (_jitter))) / 1000)
 
+/* minimum timestamp delta between 2 interrupts for measuring period (20ms) */
+#define INV_SENSORS_MIN_IT_DELTA	(20 * NSEC_PER_MSEC)
+
 /* Add a new value inside an accumulator and update the estimate value */
 static void inv_update_acc(struct inv_sensors_timestamp_acc *acc, u32 val)
 {
@@ -122,7 +125,7 @@ void inv_sensors_timestamp_interrupt(struct inv_sensors_timestamp *ts,
 				     size_t sample_nb, s64 timestamp)
 {
 	struct inv_sensors_timestamp_interval *it;
-	s64 delta, interval;
+	s64 delta, delta_threshold, interval;
 	u32 period;
 	bool valid = false;
 
@@ -136,15 +139,32 @@ void inv_sensors_timestamp_interrupt(struct inv_sensors_timestamp *ts,
 		ts->timestamp = timestamp - interval;
 	}
 
+	/* update delta timestamps and estimated period */
+	it = &ts->delta;
+	ts->delta_counter += sample_nb;
+	delta = timestamp - it->up;
+	delta_threshold = INV_SENSORS_TIMESTAMP_MIN(INV_SENSORS_MIN_IT_DELTA, ts->chip.jitter);
+	if (delta >= delta_threshold) {
+		it->lo = it->up;
+		it->up = timestamp;
+		if (it->lo != 0) {
+			/* compute period: delta time divided by number of samples */
+			delta = it->up - it->lo;
+			period = div_s64(delta, ts->delta_counter);
+			inv_update_chip_period(ts, period);
+		}
+		ts->delta_counter = 0;
+	}
+
 	/* update interrupt timestamp and compute chip and sensor periods */
 	it = &ts->it;
 	it->lo = it->up;
 	it->up = timestamp;
 	delta = it->up - it->lo;
 	if (it->lo != 0) {
-		/* compute period: delta time divided by number of samples */
+		/* compute period and check validity */
 		period = div_s64(delta, sample_nb);
-		valid = inv_update_chip_period(ts, period);
+		valid = inv_validate_period(ts, period);
 	}
 
 	/* if interrupt interval is valid, sync with interrupt timestamp */
diff --git a/include/linux/iio/common/inv_sensors_timestamp.h b/include/linux/iio/common/inv_sensors_timestamp.h
index e4e720e6f4b7..4f08204ede3b 100644
--- a/include/linux/iio/common/inv_sensors_timestamp.h
+++ b/include/linux/iio/common/inv_sensors_timestamp.h
@@ -46,6 +46,8 @@ struct inv_sensors_timestamp_acc {
  * @min_period:		minimal acceptable clock period
  * @max_period:		maximal acceptable clock period
  * @it:			interrupts interval timestamps
+ * @delta:		interval timestamps between several interrupts
+ * @delta_counter:	number of data samples in the delta interval
  * @timestamp:		store last timestamp for computing next data timestamp
  * @mult:		current internal period multiplier
  * @new_mult:		new set internal period multiplier (not yet effective)
@@ -57,6 +59,8 @@ struct inv_sensors_timestamp {
 	u32 min_period;
 	u32 max_period;
 	struct inv_sensors_timestamp_interval it;
+	struct inv_sensors_timestamp_interval delta;
+	u32 delta_counter;
 	s64 timestamp;
 	u32 mult;
 	u32 new_mult;
@@ -88,6 +92,8 @@ static inline void inv_sensors_timestamp_reset(struct inv_sensors_timestamp *ts)
 	const struct inv_sensors_timestamp_interval interval_init = {0LL, 0LL};
 
 	ts->it = interval_init;
+	ts->delta = interval_init;
+	ts->delta_counter = 0;
 	ts->timestamp = 0;
 }
 

-- 
2.54.0