* [PATCH] hwmon: sht3x: set initial jiffies to last_update @ 2016-07-08 2:46 Matt Ranostay 2016-07-08 7:56 ` Jean Delvare 0 siblings, 1 reply; 6+ messages in thread From: Matt Ranostay @ 2016-07-08 2:46 UTC (permalink / raw) To: linux-hwmon; +Cc: Matt Ranostay, Guenter Roeck, David Frey Handling the wraparound requires the data->last_update to be set to an initial jiffies value. Otherwise you can start in a state where the sensor will never request a reading. Cc: Guenter Roeck <linux@roeck-us.net> Cc: David Frey <david.frey@sensirion.com> Signed-off-by: Matt Ranostay <mranostay@gmail.com> --- drivers/hwmon/sht3x.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/hwmon/sht3x.c b/drivers/hwmon/sht3x.c index 450645b6053d..05a925257938 100644 --- a/drivers/hwmon/sht3x.c +++ b/drivers/hwmon/sht3x.c @@ -722,7 +722,7 @@ static int sht3x_probe(struct i2c_client *client, data->setup.blocking_io = false; data->setup.high_precision = true; data->mode = 0; - data->last_update = 0; + data->last_update = jiffies; data->client = client; crc8_populate_msb(sht3x_crc8_table, SHT3X_CRC8_POLYNOMIAL); -- 2.7.4 ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] hwmon: sht3x: set initial jiffies to last_update 2016-07-08 2:46 [PATCH] hwmon: sht3x: set initial jiffies to last_update Matt Ranostay @ 2016-07-08 7:56 ` Jean Delvare 2016-07-09 0:22 ` Matt Ranostay 0 siblings, 1 reply; 6+ messages in thread From: Jean Delvare @ 2016-07-08 7:56 UTC (permalink / raw) To: Matt Ranostay; +Cc: linux-hwmon, Guenter Roeck, David Frey Hi Matt, On jeu., 2016-07-07 at 19:46 -0700, Matt Ranostay wrote: > Handling the wraparound requires the data->last_update to be set to an > initial jiffies value. Otherwise you can start in a state where the > sensor will never request a reading. I can't see how. As I read the code, in the worst case, readings can be blocked for interval_ms (2 seconds maximum.) > > Cc: Guenter Roeck <linux@roeck-us.net> > Cc: David Frey <david.frey@sensirion.com> > Signed-off-by: Matt Ranostay <mranostay@gmail.com> > --- > drivers/hwmon/sht3x.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/hwmon/sht3x.c b/drivers/hwmon/sht3x.c > index 450645b6053d..05a925257938 100644 > --- a/drivers/hwmon/sht3x.c > +++ b/drivers/hwmon/sht3x.c > @@ -722,7 +722,7 @@ static int sht3x_probe(struct i2c_client *client, > data->setup.blocking_io = false; > data->setup.high_precision = true; > data->mode = 0; > - data->last_update = 0; > + data->last_update = jiffies; > data->client = client; > crc8_populate_msb(sht3x_crc8_table, SHT3X_CRC8_POLYNOMIAL); > Both look equally wrong to me. With your proposal, accessing the sysfs attributes right after loading the driver will not trigger a reading. In order to guarantee that the first access will trigger a reading, data->last_update should be initialized to jiffies - msecs_to_jiffies(2000) (the maximum interval value.) -- Jean Delvare SUSE L3 Support ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] hwmon: sht3x: set initial jiffies to last_update 2016-07-08 7:56 ` Jean Delvare @ 2016-07-09 0:22 ` Matt Ranostay 2016-07-21 6:10 ` Jean Delvare 0 siblings, 1 reply; 6+ messages in thread From: Matt Ranostay @ 2016-07-09 0:22 UTC (permalink / raw) To: Jean Delvare; +Cc: linux-hwmon, Guenter Roeck, David Frey On Fri, Jul 8, 2016 at 12:56 AM, Jean Delvare <jdelvare@suse.de> wrote: > Hi Matt, > > On jeu., 2016-07-07 at 19:46 -0700, Matt Ranostay wrote: >> Handling the wraparound requires the data->last_update to be set to an >> initial jiffies value. Otherwise you can start in a state where the >> sensor will never request a reading. > > I can't see how. As I read the code, in the worst case, readings can be > blocked for interval_ms (2 seconds maximum.) On 64-bit systems this is never an issue because the jiffies counter will never wrap around. But my system is a 32-bit ARM core, so the the kernel sets the initial value to 0xfffb6c20 so it will wrap around in 5 minutes to find buggy code. So looking at time_after(0xfffb6c20, 0) will return false always till it finally rolls over. > >> >> Cc: Guenter Roeck <linux@roeck-us.net> >> Cc: David Frey <david.frey@sensirion.com> >> Signed-off-by: Matt Ranostay <mranostay@gmail.com> >> --- >> drivers/hwmon/sht3x.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/hwmon/sht3x.c b/drivers/hwmon/sht3x.c >> index 450645b6053d..05a925257938 100644 >> --- a/drivers/hwmon/sht3x.c >> +++ b/drivers/hwmon/sht3x.c >> @@ -722,7 +722,7 @@ static int sht3x_probe(struct i2c_client *client, >> data->setup.blocking_io = false; >> data->setup.high_precision = true; >> data->mode = 0; >> - data->last_update = 0; >> + data->last_update = jiffies; >> data->client = client; >> crc8_populate_msb(sht3x_crc8_table, SHT3X_CRC8_POLYNOMIAL); >> > > Both look equally wrong to me. With your proposal, accessing the sysfs > attributes right after loading the driver will not trigger a reading. > > In order to guarantee that the first access will trigger a reading, > data->last_update should be initialized to jiffies - > msecs_to_jiffies(2000) (the maximum interval value.) Ok that is fine. Rather do jiffies + (2 * HZ) > > -- > Jean Delvare > SUSE L3 Support > ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] hwmon: sht3x: set initial jiffies to last_update 2016-07-09 0:22 ` Matt Ranostay @ 2016-07-21 6:10 ` Jean Delvare 2016-07-24 23:50 ` Matt Ranostay 0 siblings, 1 reply; 6+ messages in thread From: Jean Delvare @ 2016-07-21 6:10 UTC (permalink / raw) To: Matt Ranostay; +Cc: linux-hwmon, Guenter Roeck, David Frey Hi Matt, On Fri, 8 Jul 2016 17:22:10 -0700, Matt Ranostay wrote: > On Fri, Jul 8, 2016 at 12:56 AM, Jean Delvare <jdelvare@suse.de> wrote: > > On jeu., 2016-07-07 at 19:46 -0700, Matt Ranostay wrote: > >> Handling the wraparound requires the data->last_update to be set to an > >> initial jiffies value. Otherwise you can start in a state where the > >> sensor will never request a reading. > > > > I can't see how. As I read the code, in the worst case, readings can be > > blocked for interval_ms (2 seconds maximum.) > > On 64-bit systems this is never an issue because the jiffies counter > will never wrap around. > > But my system is a 32-bit ARM core, so the the kernel sets the initial > value to 0xfffb6c20 so it will wrap around in 5 minutes to find buggy > code. > > So looking at time_after(0xfffb6c20, 0) will return false always till > it finally rolls over. I've always been confused by how jiffies wrapping is handled. So I tested it, and you are correct. > >> Cc: Guenter Roeck <linux@roeck-us.net> > >> Cc: David Frey <david.frey@sensirion.com> > >> Signed-off-by: Matt Ranostay <mranostay@gmail.com> > >> --- > >> drivers/hwmon/sht3x.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/drivers/hwmon/sht3x.c b/drivers/hwmon/sht3x.c > >> index 450645b6053d..05a925257938 100644 > >> --- a/drivers/hwmon/sht3x.c > >> +++ b/drivers/hwmon/sht3x.c > >> @@ -722,7 +722,7 @@ static int sht3x_probe(struct i2c_client *client, > >> data->setup.blocking_io = false; > >> data->setup.high_precision = true; > >> data->mode = 0; > >> - data->last_update = 0; > >> + data->last_update = jiffies; > >> data->client = client; > >> crc8_populate_msb(sht3x_crc8_table, SHT3X_CRC8_POLYNOMIAL); > >> > > > > Both look equally wrong to me. With your proposal, accessing the sysfs > > attributes right after loading the driver will not trigger a reading. > > > > In order to guarantee that the first access will trigger a reading, > > data->last_update should be initialized to jiffies - > > msecs_to_jiffies(2000) (the maximum interval value.) > > Ok that is fine. Rather do jiffies + (2 * HZ) 2 * HZ is fine. But it's minus, not plus. You want to initialize the last update time to 2 seconds BEFORE the driver is being loaded, so that the current time is at least 2 seconds AFTER the (fake) last update at first access. And you should subtract another jiffy to be on the safe side. Can you please send an updated patch? -- Jean Delvare SUSE L3 Support ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] hwmon: sht3x: set initial jiffies to last_update 2016-07-21 6:10 ` Jean Delvare @ 2016-07-24 23:50 ` Matt Ranostay 2016-07-25 8:42 ` Jean Delvare 0 siblings, 1 reply; 6+ messages in thread From: Matt Ranostay @ 2016-07-24 23:50 UTC (permalink / raw) To: Jean Delvare, linux-iio@vger.kernel.org, Jonathan Cameron Cc: linux-hwmon, Guenter Roeck, David Frey On Wed, Jul 20, 2016 at 11:10 PM, Jean Delvare <jdelvare@suse.de> wrote: > Hi Matt, > > On Fri, 8 Jul 2016 17:22:10 -0700, Matt Ranostay wrote: >> On Fri, Jul 8, 2016 at 12:56 AM, Jean Delvare <jdelvare@suse.de> wrote: >> > On jeu., 2016-07-07 at 19:46 -0700, Matt Ranostay wrote: >> >> Handling the wraparound requires the data->last_update to be set to an >> >> initial jiffies value. Otherwise you can start in a state where the >> >> sensor will never request a reading. >> > >> > I can't see how. As I read the code, in the worst case, readings can be >> > blocked for interval_ms (2 seconds maximum.) >> >> On 64-bit systems this is never an issue because the jiffies counter >> will never wrap around. >> >> But my system is a 32-bit ARM core, so the the kernel sets the initial >> value to 0xfffb6c20 so it will wrap around in 5 minutes to find buggy >> code. >> >> So looking at time_after(0xfffb6c20, 0) will return false always till >> it finally rolls over. > > I've always been confused by how jiffies wrapping is handled. So I > tested it, and you are correct. > Yeah but of course on 64-bit systems most just use the lower 32-bits of the jiffies counter. But since that could rollover, and the unlikely event no sensor data was read for ~57 days you could be in the same state that couldn't get a data sample .... Not sure if we want to check this edge case.. and also this effects a few iio drivers (mostly mine :)) if we really care about this. >> >> Cc: Guenter Roeck <linux@roeck-us.net> >> >> Cc: David Frey <david.frey@sensirion.com> >> >> Signed-off-by: Matt Ranostay <mranostay@gmail.com> >> >> --- >> >> drivers/hwmon/sht3x.c | 2 +- >> >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> >> >> diff --git a/drivers/hwmon/sht3x.c b/drivers/hwmon/sht3x.c >> >> index 450645b6053d..05a925257938 100644 >> >> --- a/drivers/hwmon/sht3x.c >> >> +++ b/drivers/hwmon/sht3x.c >> >> @@ -722,7 +722,7 @@ static int sht3x_probe(struct i2c_client *client, >> >> data->setup.blocking_io = false; >> >> data->setup.high_precision = true; >> >> data->mode = 0; >> >> - data->last_update = 0; >> >> + data->last_update = jiffies; >> >> data->client = client; >> >> crc8_populate_msb(sht3x_crc8_table, SHT3X_CRC8_POLYNOMIAL); >> >> >> > >> > Both look equally wrong to me. With your proposal, accessing the sysfs >> > attributes right after loading the driver will not trigger a reading. >> > >> > In order to guarantee that the first access will trigger a reading, >> > data->last_update should be initialized to jiffies - >> > msecs_to_jiffies(2000) (the maximum interval value.) >> >> Ok that is fine. Rather do jiffies + (2 * HZ) > > 2 * HZ is fine. But it's minus, not plus. You want to initialize the > last update time to 2 seconds BEFORE the driver is being loaded, so > that the current time is at least 2 seconds AFTER the (fake) last > update at first access. And you should subtract another jiffy to be on > the safe side. > > Can you please send an updated patch? Sure will do. > > -- > Jean Delvare > SUSE L3 Support ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] hwmon: sht3x: set initial jiffies to last_update 2016-07-24 23:50 ` Matt Ranostay @ 2016-07-25 8:42 ` Jean Delvare 0 siblings, 0 replies; 6+ messages in thread From: Jean Delvare @ 2016-07-25 8:42 UTC (permalink / raw) To: Matt Ranostay Cc: linux-iio, Jonathan Cameron, linux-hwmon, Guenter Roeck, David Frey Hi Matt, On Sun, 24 Jul 2016 16:50:39 -0700, Matt Ranostay wrote: > On Wed, Jul 20, 2016 at 11:10 PM, Jean Delvare <jdelvare@suse.de> wrote: > > On Fri, 8 Jul 2016 17:22:10 -0700, Matt Ranostay wrote: > >> On Fri, Jul 8, 2016 at 12:56 AM, Jean Delvare <jdelvare@suse.de> wrote: > >> > On jeu., 2016-07-07 at 19:46 -0700, Matt Ranostay wrote: > >> >> Handling the wraparound requires the data->last_update to be set to an > >> >> initial jiffies value. Otherwise you can start in a state where the > >> >> sensor will never request a reading. > >> > > >> > I can't see how. As I read the code, in the worst case, readings can be > >> > blocked for interval_ms (2 seconds maximum.) > >> > >> On 64-bit systems this is never an issue because the jiffies counter > >> will never wrap around. > >> > >> But my system is a 32-bit ARM core, so the the kernel sets the initial > >> value to 0xfffb6c20 so it will wrap around in 5 minutes to find buggy > >> code. > >> > >> So looking at time_after(0xfffb6c20, 0) will return false always till > >> it finally rolls over. > > > > I've always been confused by how jiffies wrapping is handled. So I > > tested it, and you are correct. > > Yeah but of course on 64-bit systems most just use the lower 32-bits > of the jiffies counter. Actually it seems the jiffies are initialized the same on 32-bit and 64-bit systems, so on 64-bit systems you'll get 33-bit values after 5 minutes, and 34-bit values after about 100 days (if HZ=1000.) But you'll never realistically wrap, you are right. > But since that could rollover, and the unlikely event no sensor data > was read for ~57 days you could be in the same state that couldn't get > a data sample .... At HZ=1000 the jiffies wrap after 49 days, IIRC, not 57. Not that it matters ;-) > Not sure if we want to check this edge case.. and also this effects a > few iio drivers (mostly mine :)) if we really care about this. All other hwmon drivers have the same problem. I can't think of a cheap way to solve this problem, nor do I think we need to. If you monitor your system, you are supposed to poll the device on a regular basis, not once every 49 days. -- Jean Delvare SUSE L3 Support ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2016-07-25 8:42 UTC | newest] Thread overview: 6+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2016-07-08 2:46 [PATCH] hwmon: sht3x: set initial jiffies to last_update Matt Ranostay 2016-07-08 7:56 ` Jean Delvare 2016-07-09 0:22 ` Matt Ranostay 2016-07-21 6:10 ` Jean Delvare 2016-07-24 23:50 ` Matt Ranostay 2016-07-25 8:42 ` Jean Delvare
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