From mboxrd@z Thu Jan 1 00:00:00 1970 From: mark.rutland@arm.com (Mark Rutland) Date: Wed, 27 Mar 2013 17:11:50 +0000 Subject: [PATCH 3/5] clocksource: arch_timer: use virtual counters In-Reply-To: <1364404312-4427-1-git-send-email-mark.rutland@arm.com> References: <1364404312-4427-1-git-send-email-mark.rutland@arm.com> Message-ID: <1364404312-4427-4-git-send-email-mark.rutland@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 travel backwards. If we do have hyp mode, and might be a KVM host, we have to use the physical timers, and require CNTVOFF to be 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 Cc: Rob Herring --- arch/arm/include/asm/arch_timer.h | 9 --------- arch/arm64/include/asm/arch_timer.h | 10 ---------- drivers/clocksource/arm_arch_timer.c | 23 +++++------------------ include/clocksource/arm_arch_timer.h | 2 +- 4 files changed, 6 insertions(+), 38 deletions(-) diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h index 7ade91d..35fea17 100644 --- a/arch/arm/include/asm/arch_timer.h +++ b/arch/arm/include/asm/arch_timer.h @@ -81,15 +81,6 @@ 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; diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h index 91e2a6a..5307737 100644 --- a/arch/arm64/include/asm/arch_timer.h +++ b/arch/arm64/include/asm/arch_timer.h @@ -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; diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c index d7ad425..2abb861 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 = { @@ -285,7 +277,7 @@ 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]; @@ -382,10 +374,5 @@ int __init arch_timer_init(void) } } - if (arch_timer_use_virtual) - arch_timer_read_counter = arch_counter_get_cntvct; - else - arch_timer_read_counter = arch_counter_get_cntpct; - return arch_timer_register(); } diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h index 2603267..3883812 100644 --- a/include/clocksource/arm_arch_timer.h +++ b/include/clocksource/arm_arch_timer.h @@ -33,7 +33,7 @@ extern int arch_timer_init(void); 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 -- 1.8.1.1