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| author | Russell King <rmk+kernel@arm.linux.org.uk> | 2015-04-13 12:36:04 +0300 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2015-04-15 00:28:07 +0300 |
| commit | 57ca654bef6c43bbbccfb2d231fd245d3f67dd46 (patch) | |
| tree | 5c76973e14228695f742c71a33d87b7b9f916149 /arch/arm | |
| parent | 37463be8658ae5fba153f4029ca3ec3f8a64fd51 (diff) | |
| download | linux-57ca654bef6c43bbbccfb2d231fd245d3f67dd46.tar.xz | |
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>
Diffstat (limited to 'arch/arm')
| -rw-r--r-- | arch/arm/lib/delay.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/arch/arm/lib/delay.c b/arch/arm/lib/delay.c index 312d43eb686a..8044591dca72 100644 --- a/arch/arm/lib/delay.c +++ b/arch/arm/lib/delay.c @@ -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; |