1 files changed, 22 insertions, 4 deletions

diff --git a/arch/arm/lib/delay.c b/arch/arm/lib/delay.c
index 5306de350133..312d43eb686a 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 @@ 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;
+}