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clocksource: arch_timer: use virtual counters

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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>
This commit is contained in:
Mark Rutland 2013-01-30 17:51:26 +00:00
parent f793c23ebb
commit 0d651e4e65
4 changed files with 6 additions and 38 deletions
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9
arch/arm/include/asm/arch_timer.h
View File

@ -80,15 +80,6 @@ static inline u32 arch_timer_get_cntfrq(void)
return val;
}
static inline u64 arch_counter_get_cntpct(void)
{
u64 cval;
isb();
asm volatile("mrrc p15, 0, %Q0, %R0, c14" : "=r" (cval));
return cval;
}
static inline u64 arch_counter_get_cntvct(void)
{
u64 cval;

10
arch/arm64/include/asm/arch_timer.h
View File

@ -110,16 +110,6 @@ static inline void __cpuinit arch_counter_set_user_access(void)
asm volatile("msr cntkctl_el1, %0" : : "r" (cntkctl));
}
static inline u64 arch_counter_get_cntpct(void)
{
u64 cval;
isb();
asm volatile("mrs %0, cntpct_el0" : "=r" (cval));
return cval;
}
static inline u64 arch_counter_get_cntvct(void)
{
u64 cval;

23
drivers/clocksource/arm_arch_timer.c
View File

@ -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();
}

2
include/clocksource/arm_arch_timer.h
View File

@ -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