| Message ID | 20200220150250.46226-1-linus.walleij@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | gpio: Switch timestamps to ktime_get_ns() | expand |
czw., 20 lut 2020 o 16:03 Linus Walleij <linus.walleij@linaro.org> napisał(a): > > The existing use of ktime_get_real_ns() in the timestamps from > the GPIO events is dubious. > > We have had several discussions about this timestamp, and it is > unclear whether userspace has ever taken into account that a > timestamp from ktime_get_real_ns() can actually move backwards > in time relative the previous timetamp, and userspace is more > likely to expect a monotonic counter. > > Background: > https://lore.kernel.org/linux-gpio/CAK8P3a1Skvm48sje8FNDPLYqyz9Lf8q0qX1QETWtyZTxuX4k1g@mail.gmail.com/ > https://marc.info/?l=linux-gpio&m=151661955709074&w=2 > > The change is ABI incompatible, but incompatible in a way that > is IMO more likely to fix future bugs rather than break current > userspace. To the best of my knowledge all userspace expects > a monotonic timestamp and users are just lucky that they very > seldom move backwards in time. > > Cc: Arnd Bergmann <arnd@arndb.de> > Signed-off-by: Linus Walleij <linus.walleij@linaro.org> > --- I too am in favor of this change. Acked-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c index 753283486037..5db16f69c13e 100644 --- a/drivers/gpio/gpiolib.c +++ b/drivers/gpio/gpiolib.c @@ -945,7 +945,7 @@ static irqreturn_t lineevent_irq_thread(int irq, void *p) * we didn't get the timestamp from lineevent_irq_handler(). */ if (!le->timestamp) - ge.timestamp = ktime_get_real_ns(); + ge.timestamp = ktime_get_ns(); else ge.timestamp = le->timestamp; @@ -983,7 +983,7 @@ static irqreturn_t lineevent_irq_handler(int irq, void *p) * Just store the timestamp in hardirq context so we get it as * close in time as possible to the actual event. */ - le->timestamp = ktime_get_real_ns(); + le->timestamp = ktime_get_ns(); return IRQ_WAKE_THREAD; }
The existing use of ktime_get_real_ns() in the timestamps from the GPIO events is dubious. We have had several discussions about this timestamp, and it is unclear whether userspace has ever taken into account that a timestamp from ktime_get_real_ns() can actually move backwards in time relative the previous timetamp, and userspace is more likely to expect a monotonic counter. Background: https://lore.kernel.org/linux-gpio/CAK8P3a1Skvm48sje8FNDPLYqyz9Lf8q0qX1QETWtyZTxuX4k1g@mail.gmail.com/ https://marc.info/?l=linux-gpio&m=151661955709074&w=2 The change is ABI incompatible, but incompatible in a way that is IMO more likely to fix future bugs rather than break current userspace. To the best of my knowledge all userspace expects a monotonic timestamp and users are just lucky that they very seldom move backwards in time. Cc: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Linus Walleij <linus.walleij@linaro.org> --- drivers/gpio/gpiolib.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)