openkylin
/
linux
mirror of https://gitee.com/openkylin/linux.git
9
0
Fork 0
Code Issues Projects Releases Wiki Activity

ARM: ensure delay timer has sufficient accuracy for delays 

We have recently had an example of someone wanting to use a 90kHz timer
for the software delay loop.

udelay() needs to have at least microsecond resolution to allow drivers
access to a delay mechanism with a reasonable chance of delaying the
period they requested within at least a 50% marging of error, especially
for small delays.

Discussion about the udelay() accuracy can be found at:
	https://lkml.org/lkml/2011/1/9/37

Reject timers which are unable to supply this level of resolution.

Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Russell King 2015-04-13 10:36:04 +01:00
parent 37463be865
commit 57ca654bef
1 changed files with 6 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
arch/arm/lib/delay.c
View File

@ -83,6 +83,12 @@ void __init register_current_timer_delay(const struct delay_timer *timer)
NSEC_PER_SEC, 3600);
res = cyc_to_ns(1ULL, new_mult, new_shift);
if (res > 1000) {
pr_err("Ignoring delay timer %ps, which has insufficient resolution of %lluns\n",
timer, res);
return;
}
if (!delay_calibrated && (!delay_res || (res < delay_res))) {
pr_info("Switching to timer-based delay loop, resolution %lluns\n", res);
delay_timer = timer;