Merge tag 'tegra-for-3.17-delay-timer' of git://git.kernel.org/pub/scm/linux/kernel/git/tegra/linux into next/soc

Merge "ARM: tegra: use us counter as delay timer" from Stephen Warren:

Tegra has a micro-second counter whose rate doesn't vary with cpufreq
changes. Register it so it can be used as the delay timer, so delays
aren't influenced by cpufreq.

* tag 'tegra-for-3.17-delay-timer' of git://git.kernel.org/pub/scm/linux/kernel/git/tegra/linux:
  clocksource: tegra: Use us counter as delay timer
  ARM: choose highest resolution delay timer
  kernel: add calibration_delay_done()

Signed-off-by: Olof Johansson <olof@lixom.net>

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;
+}

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);

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();
 }