[PATCH v2 2/2] clocksource: arm_arch_timer: Correct fault programming of CNTKCTL_EL1.EVNTI

[Keqian Zhu]

ARM virtual counter supports event stream, it can only trigger an event
when the trigger bit (the value of CNTKCTL_EL1.EVNTI) of CNTVCT_EL0 changes,
so the actual period of event stream is 2^(cntkctl_evnti + 1). For example,
when the trigger bit is 0, then virtual counter trigger an event for every
two cycles.

Fixes: 037f637767a8 ("drivers: clocksource: add support for
       ARM architected timer event stream")
Suggested-by: Marc Zyngier <maz@xxxxxxxxxx>
Signed-off-by: Keqian Zhu <zhukeqian1@xxxxxxxxxx>
---
 drivers/clocksource/arm_arch_timer.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 777d38c..e3b2ee0 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -824,10 +824,14 @@ static void arch_timer_configure_evtstream(void)
 {
 	int evt_stream_div, pos;
 
-	/* Find the closest power of two to the divisor */
-	evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ;
+	/*
+	 * Find the closest power of two to the divisor. As the event
+	 * stream can at most be generated at half the frequency of the
+	 * counter, use half the frequency when computing the divider.
+	 */
+	evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ / 2;
 	pos = fls(evt_stream_div);
-	if (pos > 1 && !(evt_stream_div & (1 << (pos - 2))))
+	if ((pos == 1) || (pos > 1 && !(evt_stream_div & (1 << (pos - 2)))))
 		pos--;
 	/* enable event stream */
 	arch_timer_evtstrm_enable(min(pos, 15));
-- 
1.8.3.1