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author | Mark Rutland <mark.rutland@arm.com> | 2013-01-30 17:51:26 +0000 |
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committer | Mark Rutland <mark.rutland@arm.com> | 2013-06-07 10:20:28 +0100 |
commit | 0d651e4e65e96989f72236bf83bd4c6e55eb6ce4 (patch) | |
tree | 85897795e32a2cc107b9c8bda0b4641785b38e8d /drivers | |
parent | f793c23ebbe5afd1cabf4a42a3a297022213756f (diff) | |
download | op-kernel-dev-0d651e4e65e96989f72236bf83bd4c6e55eb6ce4.zip op-kernel-dev-0d651e4e65e96989f72236bf83bd4c6e55eb6ce4.tar.gz |
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 <mark.rutland@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: Rob Herring <rob.herring@calxeda.com>
Diffstat (limited to 'drivers')
-rw-r--r-- | drivers/clocksource/arm_arch_timer.c | 23 |
1 files changed, 5 insertions, 18 deletions
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c index a2b2541..053d846 100644 --- a/drivers/clocksource/arm_arch_timer.c +++ b/drivers/clocksource/arm_arch_timer.c @@ -186,27 +186,19 @@ u32 arch_timer_get_rate(void) return arch_timer_rate; } -/* - * Some external users of arch_timer_read_counter (e.g. sched_clock) may try to - * call it before it has been initialised. Rather than incur a performance - * penalty checking for initialisation, provide a default implementation that - * won't lead to time appearing to jump backwards. - */ -static u64 arch_timer_read_zero(void) +u64 arch_timer_read_counter(void) { - return 0; + return arch_counter_get_cntvct(); } -u64 (*arch_timer_read_counter)(void) = arch_timer_read_zero; - static cycle_t arch_counter_read(struct clocksource *cs) { - return arch_timer_read_counter(); + return arch_counter_get_cntvct(); } static cycle_t arch_counter_read_cc(const struct cyclecounter *cc) { - return arch_timer_read_counter(); + return arch_counter_get_cntvct(); } static struct clocksource clocksource_counter = { @@ -287,7 +279,7 @@ static int __init arch_timer_register(void) cyclecounter.mult = clocksource_counter.mult; cyclecounter.shift = clocksource_counter.shift; timecounter_init(&timecounter, &cyclecounter, - arch_counter_get_cntpct()); + arch_counter_get_cntvct()); if (arch_timer_use_virtual) { ppi = arch_timer_ppi[VIRT_PPI]; @@ -376,11 +368,6 @@ static void __init arch_timer_init(struct device_node *np) } } - if (arch_timer_use_virtual) - arch_timer_read_counter = arch_counter_get_cntvct; - else - arch_timer_read_counter = arch_counter_get_cntpct; - arch_timer_register(); arch_timer_arch_init(); } |