Re: [PATCH] gpio: Switch timestamps to ktime_get_ns()

[Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>]

czw., 20 lut 2020 o 16:03 Linus Walleij <linus.walleij@xxxxxxxxxx> 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@xxxxxxxxxxxxxx/
> 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@xxxxxxxx>
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> ---

I too am in favor of this change.

Acked-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>