On Fri, Jul 8, 2016 at 12:56 AM, Jean Delvare <jdelvare@xxxxxxx> 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@xxxxxxxxxxxx> >> Cc: David Frey <david.frey@xxxxxxxxxxxxx> >> Signed-off-by: Matt Ranostay <mranostay@xxxxxxxxx> >> --- >> 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-hwmon" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
