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Commit 0d651e4e authored by Mark Rutland's avatar Mark Rutland
Browse files

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: default avatarMark Rutland <mark.rutland@arm.com>
Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Acked-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Acked-by: default avatarSantosh Shilimkar <santosh.shilimkar@ti.com>
Cc: Rob Herring <rob.herring@calxeda.com>
parent f793c23e

arch/arm/include/asm/arch_timer.h

+0 −9
Original line number Diff line number Diff line
@@ -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;

arch/arm64/include/asm/arch_timer.h

+0 −10
Original line number Diff line number Diff line
@@ -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;

drivers/clocksource/arm_arch_timer.c

+5 −18
Original line number Diff line number Diff line
@@ -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();

}

include/clocksource/arm_arch_timer.h

+1 −1
Original line number Diff line number Diff line
@@ -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