ARM: choose highest resolution delay timer
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>
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@arm.com>
*/
+#include <linux/clocksource.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/kernel.h>
@@ -36,6 +37,7 @@
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 @@
}
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 @@
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 @@
delay_calibrated = true;
return lpj_fine;
}
+
+void calibration_delay_done(void)
+{
+ delay_calibrated = true;
+}