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ARM: choose highest resolution delay timer

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In case there are several possible delay timers, choose the one with the
highest resolution. This code relies on the fact secondary CPUs have not yet
been brought online when register_current_timer_delay() is called. This is
ensured by implementing calibration_delay_done(),

Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
This commit is contained in:
Peter De Schrijver 2014-06-12 18:58:28 +03:00 committed by Stephen Warren
parent e6639117d6
commit 5930c1a1f7
1 changed files with 22 additions and 4 deletions
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26
arch/arm/lib/delay.c
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@ -19,6 +19,7 @@
* Author: Will Deacon <will.deacon@arm.com>
*/
#include <linux/clocksource.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/kernel.h>
@ -36,6 +37,7 @@ struct arm_delay_ops arm_delay_ops = {
static const struct delay_timer *delay_timer;
static bool delay_calibrated;
static u64 delay_res;
int read_current_timer(unsigned long *timer_val)
{
@ -47,6 +49,11 @@ int read_current_timer(unsigned long *timer_val)
}
EXPORT_SYMBOL_GPL(read_current_timer);
static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
{
return (cyc * mult) >> shift;
}
static void __timer_delay(unsigned long cycles)
{
cycles_t start = get_cycles();
@ -69,18 +76,24 @@ static void __timer_udelay(unsigned long usecs)
void __init register_current_timer_delay(const struct delay_timer *timer)
{
if (!delay_calibrated) {
pr_info("Switching to timer-based delay loop\n");
u32 new_mult, new_shift;
u64 res;
clocks_calc_mult_shift(&new_mult, &new_shift, timer->freq,
NSEC_PER_SEC, 3600);
res = cyc_to_ns(1ULL, new_mult, new_shift);
if (!delay_calibrated && (!delay_res || (res < delay_res))) {
pr_info("Switching to timer-based delay loop, resolution %lluns\n", res);
delay_timer = timer;
lpj_fine = timer->freq / HZ;
delay_res = res;
/* cpufreq may scale loops_per_jiffy, so keep a private copy */
arm_delay_ops.ticks_per_jiffy = lpj_fine;
arm_delay_ops.delay = __timer_delay;
arm_delay_ops.const_udelay = __timer_const_udelay;
arm_delay_ops.udelay = __timer_udelay;
delay_calibrated = true;
} else {
pr_info("Ignoring duplicate/late registration of read_current_timer delay\n");
}
@ -91,3 +104,8 @@ unsigned long calibrate_delay_is_known(void)
delay_calibrated = true;
return lpj_fine;
}
void calibration_delay_done(void)
{
delay_calibrated = true;
}