[PATCH v4 3/7] ARM: architected timers: Add A15 specific sched_clock implementation

[Marc Zyngier]

Provide an A15 sched_clock implementation using the virtual counter,
which is thought to be more useful than the physical one in a
virtualised environment, as it can offset the time spent in another
VM or the hypervisor.

Acked-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
---
 arch/arm/include/asm/arch_timer.h |    6 ++++++
 arch/arm/kernel/arch_timer.c      |   25 +++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 0 deletions(-)

diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
index 827305d..dc008c6 100644
--- a/arch/arm/include/asm/arch_timer.h
+++ b/arch/arm/include/asm/arch_timer.h
@@ -9,11 +9,17 @@ struct arch_timer {
 
 #ifdef CONFIG_ARM_ARCH_TIMER
 int arch_timer_register(struct arch_timer *);
+int arch_timer_sched_clock_init(void);
 #else
 static inline int arch_timer_register(struct arch_timer *at)
 {
 	return -ENXIO;
 }
+
+static inline int arch_timer_sched_clock_init(void)
+{
+	return -ENXIO;
+}
 #endif
 
 #endif
diff --git a/arch/arm/kernel/arch_timer.c b/arch/arm/kernel/arch_timer.c
index bb9a8b4..dd90704 100644
--- a/arch/arm/kernel/arch_timer.c
+++ b/arch/arm/kernel/arch_timer.c
@@ -23,6 +23,7 @@
 #include <asm/localtimer.h>
 #include <asm/arch_timer.h>
 #include <asm/system_info.h>
+#include <asm/sched_clock.h>
 
 static unsigned long arch_timer_rate;
 static int arch_timer_ppi;
@@ -204,6 +205,18 @@ static inline cycle_t arch_counter_get_cntvct(void)
 	return ((cycle_t) cvalh << 32) | cvall;
 }
 
+static u32 notrace arch_counter_get_cntvct32(void)
+{
+	cycle_t cntvct = arch_counter_get_cntvct();
+
+	/*
+	 * The sched_clock infrastructure only knows about counters
+	 * with at most 32bits. Forget about the upper 24 bits for the
+	 * time being...
+	 */
+	return (u32)(cntvct & (u32)~0);
+}
+
 static cycle_t arch_counter_read(struct clocksource *cs)
 {
 	return arch_counter_get_cntpct();
@@ -286,3 +299,15 @@ out_free:
 
 	return err;
 }
+
+int __init arch_timer_sched_clock_init(void)
+{
+	int err;
+
+	err = arch_timer_available();
+	if (err)
+		return err;
+
+	setup_sched_clock(arch_counter_get_cntvct32, 32, arch_timer_rate);
+	return 0;
+}
-- 
1.7.7.1