[PATCH] arm64: arch_timer: Ensure timer is enabled before using istatus

[Shaokun Zhang]

From: Nianyao Tang <tangnianyao at huawei.com>

In Arm ARM spec, there is a description for timer control register, when
the value of the ENABLE bit is 0, the ISTATUS field is UNKNOWN. We shall
only read and use ISTATUS when ENABLE is 1, otherwise ISTATUS may be
invalid.

Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Daniel Lezcano <daniel.lezcano at linaro.org>
Signed-off-by: Nianyao Tang <tangnianyao at huawei.com>
Signed-off-by: Shaokun Zhang <zhangshaokun at hisilicon.com>
---
 drivers/clocksource/arm_arch_timer.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 6c3e84180146..0bbc2715de79 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -641,7 +641,8 @@ static __always_inline irqreturn_t timer_handler(const int access,
 	unsigned long ctrl;
 
 	ctrl = arch_timer_reg_read(access, ARCH_TIMER_REG_CTRL, evt);
-	if (ctrl & ARCH_TIMER_CTRL_IT_STAT) {
+	if ((ctrl & ARCH_TIMER_CTRL_ENABLE) &&
+		(ctrl & ARCH_TIMER_CTRL_IT_STAT)) {
 		ctrl |= ARCH_TIMER_CTRL_IT_MASK;
 		arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, evt);
 		evt->event_handler(evt);
-- 
2.7.4