[PATCH v3 1/3] clocksource/vt8500: Increase the minimum delta

[v1ron@mail.ru (Roman Volkov)]

From: Roman Volkov <rvolkov@v1ros.org>

The vt8500 clocksource driver declares itself as capable to handle the
minimum delay of 4 cycles by passing the value into
clockevents_config_and_register(). The vt8500_timer_set_next_event()
requires the passed cycles value to be at least 16. The impact is that
userspace hangs in nanosleep() calls with small delay intervals.

This problem is reproducible in Linux 4.2 starting from:
c6eb3f70d448 ('hrtimer: Get rid of hrtimer softirq')

Signed-off-by: Roman Volkov <rvolkov@v1ros.org>
Acked-by: Alexey Charkov <alchark@gmail.com>
---
 drivers/clocksource/vt8500_timer.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/clocksource/vt8500_timer.c b/drivers/clocksource/vt8500_timer.c
index a92e94b..dfc3bb4 100644
--- a/drivers/clocksource/vt8500_timer.c
+++ b/drivers/clocksource/vt8500_timer.c
@@ -50,6 +50,8 @@
 
 #define msecs_to_loops(t) (loops_per_jiffy / 1000 * HZ * t)
 
+#define MIN_OSCR_DELTA		16
+
 static void __iomem *regbase;
 
 static cycle_t vt8500_timer_read(struct clocksource *cs)
@@ -80,7 +82,7 @@ static int vt8500_timer_set_next_event(unsigned long cycles,
 		cpu_relax();
 	writel((unsigned long)alarm, regbase + TIMER_MATCH_VAL);
 
-	if ((signed)(alarm - clocksource.read(&clocksource)) <= 16)
+	if ((signed)(alarm - clocksource.read(&clocksource)) <= MIN_OSCR_DELTA)
 		return -ETIME;
 
 	writel(1, regbase + TIMER_IER_VAL);
@@ -151,7 +153,7 @@ static void __init vt8500_timer_init(struct device_node *np)
 		pr_err("%s: setup_irq failed for %s\n", __func__,
 							clockevent.name);
 	clockevents_config_and_register(&clockevent, VT8500_TIMER_HZ,
-					4, 0xf0000000);
+					MIN_OSCR_DELTA * 2, 0xf0000000);
 }
 
 CLOCKSOURCE_OF_DECLARE(vt8500, "via,vt8500-timer", vt8500_timer_init);
-- 
2.6.2