Merge tag 'timer-for-tip' of git://git.pengutronix.de/git/ukl/linux into clockevents/3.12-fixesclockevents/3.12-fixes

The first patch in this pull request fixes an old integer rounding bug in the
timer core that was (and still is) worked around in a few arch's timer code.
The second patch drops such a work around now that the core is fixed.

2 files changed, 52 insertions, 20 deletions

diff --git a/arch/arm/mach-at91/at91rm9200_time.c b/arch/arm/mach-at91/at91rm9200_time.c
index f607deb40f4d..bc7b363a3083 100644
--- a/arch/arm/mach-at91/at91rm9200_time.c
+++ b/arch/arm/mach-at91/at91rm9200_time.c
@@ -174,7 +174,6 @@ clkevt32k_next_event(unsigned long delta, struct clock_event_device *dev)
 static struct clock_event_device clkevt = {
 	.name		= "at91_tick",
 	.features	= CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
-	.shift		= 32,
 	.rating		= 150,
 	.set_next_event	= clkevt32k_next_event,
 	.set_mode	= clkevt32k_mode,
@@ -265,11 +264,9 @@ void __init at91rm9200_timer_init(void)
 	at91_st_write(AT91_ST_RTMR, 1);
 
 	/* Setup timer clockevent, with minimum of two ticks (important!!) */
-	clkevt.mult = div_sc(AT91_SLOW_CLOCK, NSEC_PER_SEC, clkevt.shift);
-	clkevt.max_delta_ns = clockevent_delta2ns(AT91_ST_ALMV, &clkevt);
-	clkevt.min_delta_ns = clockevent_delta2ns(2, &clkevt) + 1;
 	clkevt.cpumask = cpumask_of(0);
-	clockevents_register_device(&clkevt);
+	clockevents_config_and_register(&clkevt, AT91_SLOW_CLOCK,
+					2, AT91_ST_ALMV);
 
 	/* register clocksource */
 	clocksource_register_hz(&clk32k, AT91_SLOW_CLOCK);
diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 38959c866789..662c5798a685 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -33,29 +33,64 @@ struct ce_unbind {
 	int res;
 };
 
-/**
- * clockevents_delta2ns - Convert a latch value (device ticks) to nanoseconds
- * @latch:	value to convert
- * @evt:	pointer to clock event device descriptor
- *
- * Math helper, returns latch value converted to nanoseconds (bound checked)
- */
-u64 clockevent_delta2ns(unsigned long latch, struct clock_event_device *evt)
+static u64 cev_delta2ns(unsigned long latch, struct clock_event_device *evt,
+			bool ismax)
 {
 	u64 clc = (u64) latch << evt->shift;
+	u64 rnd;
 
 	if (unlikely(!evt->mult)) {
 		evt->mult = 1;
 		WARN_ON(1);
 	}
+	rnd = (u64) evt->mult - 1;
+
+	/*
+	 * Upper bound sanity check. If the backwards conversion is
+	 * not equal latch, we know that the above shift overflowed.
+	 */
+	if ((clc >> evt->shift) != (u64)latch)
+		clc = ~0ULL;
+
+	/*
+	 * Scaled math oddities:
+	 *
+	 * For mult <= (1 << shift) we can safely add mult - 1 to
+	 * prevent integer rounding loss. So the backwards conversion
+	 * from nsec to device ticks will be correct.
+	 *
+	 * For mult > (1 << shift), i.e. device frequency is > 1GHz we
+	 * need to be careful. Adding mult - 1 will result in a value
+	 * which when converted back to device ticks can be larger
+	 * than latch by up to (mult - 1) >> shift. For the min_delta
+	 * calculation we still want to apply this in order to stay
+	 * above the minimum device ticks limit. For the upper limit
+	 * we would end up with a latch value larger than the upper
+	 * limit of the device, so we omit the add to stay below the
+	 * device upper boundary.
+	 *
+	 * Also omit the add if it would overflow the u64 boundary.
+	 */
+	if ((~0ULL - clc > rnd) &&
+	    (!ismax || evt->mult <= (1U << evt->shift)))
+		clc += rnd;
 
 	do_div(clc, evt->mult);
-	if (clc < 1000)
-		clc = 1000;
-	if (clc > KTIME_MAX)
-		clc = KTIME_MAX;
 
-	return clc;
+	/* Deltas less than 1usec are pointless noise */
+	return clc > 1000 ? clc : 1000;
+}
+
+/**
+ * clockevents_delta2ns - Convert a latch value (device ticks) to nanoseconds
+ * @latch:	value to convert
+ * @evt:	pointer to clock event device descriptor
+ *
+ * Math helper, returns latch value converted to nanoseconds (bound checked)
+ */
+u64 clockevent_delta2ns(unsigned long latch, struct clock_event_device *evt)
+{
+	return cev_delta2ns(latch, evt, false);
 }
 EXPORT_SYMBOL_GPL(clockevent_delta2ns);
 
@@ -380,8 +415,8 @@ void clockevents_config(struct clock_event_device *dev, u32 freq)
 		sec = 600;
 
 	clockevents_calc_mult_shift(dev, freq, sec);
-	dev->min_delta_ns = clockevent_delta2ns(dev->min_delta_ticks, dev);
-	dev->max_delta_ns = clockevent_delta2ns(dev->max_delta_ticks, dev);
+	dev->min_delta_ns = cev_delta2ns(dev->min_delta_ticks, dev, false);
+	dev->max_delta_ns = cev_delta2ns(dev->max_delta_ticks, dev, true);
 }
 
 /**