From 0d651e4e65e96989f72236bf83bd4c6e55eb6ce4 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Wed, 30 Jan 2013 17:51:26 +0000 Subject: clocksource: arch_timer: use virtual counters Switching between reading the virtual or physical counters is problematic, as some core code wants a view of time before we're fully set up. Using a function pointer and switching the source after the first read can make time appear to go backwards, and having a check in the read function is an unfortunate block on what we want to be a fast path. Instead, this patch makes us always use the virtual counters. If we're a guest, or don't have hyp mode, we'll use the virtual timers, and as such don't care about CNTVOFF as long as it doesn't change in such a way as to make time appear to travel backwards. As the guest will use the virtual timers, a (potential) KVM host must use the physical timers (which can wake up the host even if they fire while a guest is executing), and hence a host must have CNTVOFF set to zero so as to have a consistent view of time between the physical timers and virtual counters. Signed-off-by: Mark Rutland Acked-by: Catalin Marinas Acked-by: Marc Zyngier Acked-by: Santosh Shilimkar Cc: Rob Herring --- include/clocksource/arm_arch_timer.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/clocksource') diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h index e6c9c4cc9b23..c463ce990c48 100644 --- a/include/clocksource/arm_arch_timer.h +++ b/include/clocksource/arm_arch_timer.h @@ -32,7 +32,7 @@ #ifdef CONFIG_ARM_ARCH_TIMER extern u32 arch_timer_get_rate(void); -extern u64 (*arch_timer_read_counter)(void); +extern u64 arch_timer_read_counter(void); extern struct timecounter *arch_timer_get_timecounter(void); #else -- cgit v1.2.3-58-ga151