diff mbox series

iio: common: ssp_sensors: use ktime_get_real_ns() timestamps

Message ID 20171127115158.2884398-1-arnd@arndb.de
State Accepted
Commit a4493f227d931006e7919dd7a46d7069c4627a3c
Headers show
Series iio: common: ssp_sensors: use ktime_get_real_ns() timestamps | expand

Commit Message

Arnd Bergmann Nov. 27, 2017, 11:51 a.m. UTC 
getnstimeofday() suffers from the overflow in y2038 on 32-bit
architectures and requires a conversion into the nanosecond format that
we want here.

This changes ssp_parse_dataframe() to use ktime_get_real_ns() directly,
which does not have that problem.

An open question is what time base should be used here. Normally
timestamps should use ktime_get_ns() or ktime_get_boot_ns() to read
monotonic time instead of "real" time, which suffers from time jumps
due to settimeofday() calls or leap seconds.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

---
 drivers/iio/common/ssp_sensors/ssp_spi.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

-- 
2.9.0

Comments

Jonathan Cameron Dec. 2, 2017, 11:49 a.m. UTC | #1 
On Mon, 27 Nov 2017 12:51:48 +0100
Arnd Bergmann <arnd@arndb.de> wrote:

> getnstimeofday() suffers from the overflow in y2038 on 32-bit

> architectures and requires a conversion into the nanosecond format that

> we want here.

> 

> This changes ssp_parse_dataframe() to use ktime_get_real_ns() directly,

> which does not have that problem.

> 

> An open question is what time base should be used here. Normally

> timestamps should use ktime_get_ns() or ktime_get_boot_ns() to read

> monotonic time instead of "real" time, which suffers from time jumps

> due to settimeofday() calls or leap seconds.

> 

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>


+cc Karol Wrona.

Fix looks fine to me, but might be nice to address that and the
question of using a monotonic clock all in one go.

This is probably a copy of an ancient piece of my stupidity
where I used the wrong clock for the core IIO timestamping
code.  We fixed that a while back by letting the user
chose the clock.  If you are running slow enough you actually
do want the 'real' time - probably never the case here though.

If we don't hear from Karol for a few weeks I'll pick this
up and we can address the wrong timestamp sometime in the
future!

Jonathan

> ---

>  drivers/iio/common/ssp_sensors/ssp_spi.c | 5 +----

>  1 file changed, 1 insertion(+), 4 deletions(-)

> 

> diff --git a/drivers/iio/common/ssp_sensors/ssp_spi.c b/drivers/iio/common/ssp_sensors/ssp_spi.c

> index 704284a475ae..2ab106bb3e03 100644

> --- a/drivers/iio/common/ssp_sensors/ssp_spi.c

> +++ b/drivers/iio/common/ssp_sensors/ssp_spi.c

> @@ -277,12 +277,9 @@ static int ssp_handle_big_data(struct ssp_data *data, char *dataframe, int *idx)

>  static int ssp_parse_dataframe(struct ssp_data *data, char *dataframe, int len)

>  {

>  	int idx, sd;

> -	struct timespec ts;

>  	struct ssp_sensor_data *spd;

>  	struct iio_dev **indio_devs = data->sensor_devs;

>  

> -	getnstimeofday(&ts);

> -

>  	for (idx = 0; idx < len;) {

>  		switch (dataframe[idx++]) {

>  		case SSP_MSG2AP_INST_BYPASS_DATA:

> @@ -329,7 +326,7 @@ static int ssp_parse_dataframe(struct ssp_data *data, char *dataframe, int len)

>  	}

>  

>  	if (data->time_syncing)

> -		data->timestamp = ts.tv_sec * 1000000000ULL + ts.tv_nsec;

> +		data->timestamp = ktime_get_real_ns();

>  

>  	return 0;

>  }
Jonathan Cameron Dec. 10, 2017, 3:03 p.m. UTC | #2 
On Sat, 2 Dec 2017 11:49:49 +0000
Jonathan Cameron <jic23@kernel.org> wrote:

> On Mon, 27 Nov 2017 12:51:48 +0100

> Arnd Bergmann <arnd@arndb.de> wrote:

> 

> > getnstimeofday() suffers from the overflow in y2038 on 32-bit

> > architectures and requires a conversion into the nanosecond format that

> > we want here.

> > 

> > This changes ssp_parse_dataframe() to use ktime_get_real_ns() directly,

> > which does not have that problem.

> > 

> > An open question is what time base should be used here. Normally

> > timestamps should use ktime_get_ns() or ktime_get_boot_ns() to read

> > monotonic time instead of "real" time, which suffers from time jumps

> > due to settimeofday() calls or leap seconds.

> > 

> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>  

> 

> +cc Karol Wrona.

> 

> Fix looks fine to me, but might be nice to address that and the

> question of using a monotonic clock all in one go.

> 

> This is probably a copy of an ancient piece of my stupidity

> where I used the wrong clock for the core IIO timestamping

> code.  We fixed that a while back by letting the user

> chose the clock.  If you are running slow enough you actually

> do want the 'real' time - probably never the case here though.

> 

> If we don't hear from Karol for a few weeks I'll pick this

> up and we can address the wrong timestamp sometime in the

> future!

> 

Applied to the togreg branch of iio.git and pushed out as testing
for the autobuilders to play with it.

Thanks,

Jonathan

> Jonathan

> 

> > ---

> >  drivers/iio/common/ssp_sensors/ssp_spi.c | 5 +----

> >  1 file changed, 1 insertion(+), 4 deletions(-)

> > 

> > diff --git a/drivers/iio/common/ssp_sensors/ssp_spi.c b/drivers/iio/common/ssp_sensors/ssp_spi.c

> > index 704284a475ae..2ab106bb3e03 100644

> > --- a/drivers/iio/common/ssp_sensors/ssp_spi.c

> > +++ b/drivers/iio/common/ssp_sensors/ssp_spi.c

> > @@ -277,12 +277,9 @@ static int ssp_handle_big_data(struct ssp_data *data, char *dataframe, int *idx)

> >  static int ssp_parse_dataframe(struct ssp_data *data, char *dataframe, int len)

> >  {

> >  	int idx, sd;

> > -	struct timespec ts;

> >  	struct ssp_sensor_data *spd;

> >  	struct iio_dev **indio_devs = data->sensor_devs;

> >  

> > -	getnstimeofday(&ts);

> > -

> >  	for (idx = 0; idx < len;) {

> >  		switch (dataframe[idx++]) {

> >  		case SSP_MSG2AP_INST_BYPASS_DATA:

> > @@ -329,7 +326,7 @@ static int ssp_parse_dataframe(struct ssp_data *data, char *dataframe, int len)

> >  	}

> >  

> >  	if (data->time_syncing)

> > -		data->timestamp = ts.tv_sec * 1000000000ULL + ts.tv_nsec;

> > +		data->timestamp = ktime_get_real_ns();

> >  

> >  	return 0;

> >  }  

> 

> --

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diff mbox series

Patch

diff --git a/drivers/iio/common/ssp_sensors/ssp_spi.c b/drivers/iio/common/ssp_sensors/ssp_spi.c
index 704284a475ae..2ab106bb3e03 100644
--- a/drivers/iio/common/ssp_sensors/ssp_spi.c
+++ b/drivers/iio/common/ssp_sensors/ssp_spi.c
@@ -277,12 +277,9 @@  static int ssp_handle_big_data(struct ssp_data *data, char *dataframe, int *idx)
 static int ssp_parse_dataframe(struct ssp_data *data, char *dataframe, int len)
 {
 	int idx, sd;
-	struct timespec ts;
 	struct ssp_sensor_data *spd;
 	struct iio_dev **indio_devs = data->sensor_devs;
 
-	getnstimeofday(&ts);
-
 	for (idx = 0; idx < len;) {
 		switch (dataframe[idx++]) {
 		case SSP_MSG2AP_INST_BYPASS_DATA:
@@ -329,7 +326,7 @@  static int ssp_parse_dataframe(struct ssp_data *data, char *dataframe, int len)
 	}
 
 	if (data->time_syncing)
-		data->timestamp = ts.tv_sec * 1000000000ULL + ts.tv_nsec;
+		data->timestamp = ktime_get_real_ns();
 
 	return 0;
 }