From f8850206e160bfe35de9ca2e726ab6d6b8cb77dd Mon Sep 17 00:00:00 2001 From: Linus Walleij Date: Thu, 20 Feb 2020 15:56:24 +0100 Subject: [PATCH] gpio: Switch timestamps to ktime_get_ns() 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 Acked-by: Bartosz Golaszewski Signed-off-by: Linus Walleij --- drivers/gpio/gpiolib.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c index 611709fd560f..2c3a9c1c76be 100644 --- a/drivers/gpio/gpiolib.c +++ b/drivers/gpio/gpiolib.c @@ -954,7 +954,7 @@ 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; @@ -995,7 +995,7 @@ 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; }