[PATCH] clocksource: arch_timer: Only use the virtual counter (CNTVCT) on arm64

Catalin Marinas catalin.marinas at arm.com
Wed Dec 10 03:02:09 PST 2014

Commit 0b46b8a718c6 (clocksource: arch_timer: Fix code to use physical
timers when requested) introduces the use of physical counters in the
ARM architected timer driver. However, he arm64 kernel uses CNTVCT in
VDSO. When booting in EL2, the kernel switches to the physical timers to
make things easier for KVM but it continues to use the virtual counter
both in user and kernel. While in such scenario CNTVCT == CNTPCT (since
CNTVOFF is initialised by the kernel to 0), we want to spot firmware
bugs corrupting CNTVOFF early (which would affect CNTVCT).

Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
Tested-by: Yingjoe Chen <yingjoe.chen at mediatek.com>
Cc: Daniel Lezcano <daniel.lezcano at linaro.org>


Do you plan to take this patch and push into mainline (ideally before -rc1)?
Otherwise we can push it via the arm64 tree.



 drivers/clocksource/arm_arch_timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 6a79fc4f900c..095c1774592c 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -462,7 +462,7 @@ static void __init arch_counter_register(unsigned type)
 	/* Register the CP15 based counter if we have one */
 	if (type & ARCH_CP15_TIMER) {
-		if (arch_timer_use_virtual)
+		if (IS_ENABLED(CONFIG_ARM64) || arch_timer_use_virtual)
 			arch_timer_read_counter = arch_counter_get_cntvct;
 			arch_timer_read_counter = arch_counter_get_cntpct;

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