3 files changed, 46 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;
+}
diff --git a/drivers/clocksource/tegra20_timer.c b/drivers/clocksource/tegra20_timer.c
index d1869f02051c..d2616ef16770 100644
--- a/drivers/clocksource/tegra20_timer.c
+++ b/drivers/clocksource/tegra20_timer.c
@@ -27,6 +27,7 @@
 #include <linux/of_address.h>
 #include <linux/of_irq.h>
 #include <linux/sched_clock.h>
+#include <linux/delay.h>
 
 #include <asm/mach/time.h>
 #include <asm/smp_twd.h>
@@ -53,6 +54,8 @@ static void __iomem *rtc_base;
 static struct timespec persistent_ts;
 static u64 persistent_ms, last_persistent_ms;
 
+static struct delay_timer tegra_delay_timer;
+
 #define timer_writel(value, reg) \
         __raw_writel(value, timer_reg_base + (reg))
 #define timer_readl(reg) \
@@ -139,6 +142,11 @@ static void tegra_read_persistent_clock(struct timespec *ts)
         *ts = *tsp;
 }
 
+static unsigned long tegra_delay_timer_read_counter_long(void)
+{
+        return readl(timer_reg_base + TIMERUS_CNTR_1US);
+}
+
 static irqreturn_t tegra_timer_interrupt(int irq, void *dev_id)
 {
         struct clock_event_device *evt = (struct clock_event_device *)dev_id;
@@ -206,6 +214,11 @@ static void __init tegra20_init_timer(struct device_node *np)
                 BUG();
         }
 
+        tegra_delay_timer.read_current_timer =
+                        tegra_delay_timer_read_counter_long;
+        tegra_delay_timer.freq = 1000000;
+        register_current_timer_delay(&tegra_delay_timer);
+
         ret = setup_irq(tegra_timer_irq.irq, &tegra_timer_irq);
         if (ret) {
                 pr_err("Failed to register timer IRQ: %d\n", ret);
diff --git a/init/calibrate.c b/init/calibrate.c
index 520702db9acc..ce635dccf3d9 100644
--- a/init/calibrate.c
+++ b/init/calibrate.c
@@ -262,6 +262,15 @@ unsigned long __attribute__((weak)) calibrate_delay_is_known(void)
         return 0;
 }
 
+/*
+ * Indicate the cpu delay calibration is done. This can be used by
+ * architectures to stop accepting delay timer registrations after this point.
+ */
+
+void __attribute__((weak)) calibration_delay_done(void)
+{
+}
+
 void calibrate_delay(void)
 {
         unsigned long lpj;
@@ -301,4 +310,6 @@ void calibrate_delay(void)
 
         loops_per_jiffy = lpj;
         printed = true;
+
+        calibration_delay_done();
 }