clocksource: arch_timer: use virtual counters

mrutland-arm · mrutland-arm · commit 0d651e4e65e9 · 2013-06-07T10:20:28.000+01:00
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 &lt;mark.rutland@arm.com&gt;
Acked-by: Catalin Marinas &lt;catalin.marinas@arm.com&gt;
Acked-by: Marc Zyngier &lt;marc.zyngier@arm.com&gt;
Acked-by: Santosh Shilimkar &lt;santosh.shilimkar@ti.com&gt;
Cc: Rob Herring &lt;rob.herring@calxeda.com&gt;
diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
@@ -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;
diff --git 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
@@ -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();
 }
diff --git 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

Original file line number	Diff line number	Diff line change
`@@ -186,27 +186,19 @@ u32 arch_timer_get_rate(void)`
`186`	`186`	`return arch_timer_rate;`
`187`	`187`	`}`
`188`	`188`
`189`		`-/*`
`190`		`- * Some external users of arch_timer_read_counter (e.g. sched_clock) may try to`
`191`		`- * call it before it has been initialised. Rather than incur a performance`
`192`		`- * penalty checking for initialisation, provide a default implementation that`
`193`		`- * won't lead to time appearing to jump backwards.`
`194`		`- */`
`195`		`-static u64 arch_timer_read_zero(void)`
	`189`	`+u64 arch_timer_read_counter(void)`
`196`	`190`	`{`
`197`		`- return 0;`
	`191`	`+ return arch_counter_get_cntvct();`
`198`	`192`	`}`
`199`	`193`
`200`		`-u64 (*arch_timer_read_counter)(void) = arch_timer_read_zero;`
`201`		`-`
`202`	`194`	`static cycle_t arch_counter_read(struct clocksource *cs)`
`203`	`195`	`{`
`204`		`- return arch_timer_read_counter();`
	`196`	`+ return arch_counter_get_cntvct();`
`205`	`197`	`}`
`206`	`198`
`207`	`199`	`static cycle_t arch_counter_read_cc(const struct cyclecounter *cc)`
`208`	`200`	`{`
`209`		`- return arch_timer_read_counter();`
	`201`	`+ return arch_counter_get_cntvct();`
`210`	`202`	`}`
`211`	`203`
`212`	`204`	`static struct clocksource clocksource_counter = {`
`@@ -287,7 +279,7 @@ static int __init arch_timer_register(void)`
`287`	`279`	`cyclecounter.mult = clocksource_counter.mult;`
`288`	`280`	`cyclecounter.shift = clocksource_counter.shift;`
`289`	`281`	`timecounter_init(&timecounter, &cyclecounter,`
`290`		`- arch_counter_get_cntpct());`
	`282`	`+ arch_counter_get_cntvct());`
`291`	`283`
`292`	`284`	`if (arch_timer_use_virtual) {`
`293`	`285`	`ppi = arch_timer_ppi[VIRT_PPI];`
`@@ -376,11 +368,6 @@ static void __init arch_timer_init(struct device_node *np)`
`376`	`368`	`}`
`377`	`369`	`}`
`378`	`370`
`379`		`- if (arch_timer_use_virtual)`
`380`		`- arch_timer_read_counter = arch_counter_get_cntvct;`
`381`		`- else`
`382`		`- arch_timer_read_counter = arch_counter_get_cntpct;`
`383`		`-`
`384`	`371`	`arch_timer_register();`
`385`	`372`	`arch_timer_arch_init();`
`386`	`373`	`}`