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@xxxxxxxxxx>
---
arch/arm/lib/delay.c | 26 ++++++++++++++++++++++----
1 files changed, 22 insertions(+), 4 deletions(-)
diff --git a/arch/arm/lib/delay.c b/arch/arm/lib/delay.c
index 5306de3..312d43e 100644
--- a/arch/arm/lib/delay.c
+++ b/arch/arm/lib/delay.c
@@ -19,6 +19,7 @@
* Author: Will Deacon <will.deacon@xxxxxxx>
*/
+#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;
+}
--
1.7.7.rc0.72.g4b5ea.dirty
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