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timers: Clarify usleep_range() function comment 

Update the usleep_range() function comment to make it clear that it can
only be used in non-atomic context.

Previously we claimed usleep_range() was a drop-in replacement for udelay()
where wakeup is flexible.  But that's only true in non-atomic contexts,
where it's possible to sleep instead of delay.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/20160531212302.28502.44995.stgit@bhelgaas-glaptop2.roam.corp.google.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Bjorn Helgaas 2016-05-31 16:23:02 -05:00 committed by Thomas Gleixner
parent 2895a5e5b3
commit b5227d03b7
1 changed files with 7 additions and 1 deletions
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8
kernel/time/timer.c
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@ -1702,9 +1702,15 @@ static void __sched do_usleep_range(unsigned long min, unsigned long max)
}
/**
* usleep_range - Drop in replacement for udelay where wakeup is flexible
* usleep_range - Sleep for an approximate time
* @min: Minimum time in usecs to sleep
* @max: Maximum time in usecs to sleep
*
* In non-atomic context where the exact wakeup time is flexible, use
* usleep_range() instead of udelay(). The sleep improves responsiveness
* by avoiding the CPU-hogging busy-wait of udelay(), and the range reduces
* power usage by allowing hrtimers to take advantage of an already-
* scheduled interrupt instead of scheduling a new one just for this sleep.
*/
void __sched usleep_range(unsigned long min, unsigned long max)
{