Some subsystems (KVM for example) need access to a cycle counter.
In the KVM case, this is used to measure the time delta between
host and guest in order to accurately generate timer events for
the guest.
Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
---
arch/arm/include/asm/arch_timer.h | 8 ++++++++
arch/arm/kernel/arch_timer.c | 25 +++++++++++++++++++++++++
2 files changed, 33 insertions(+)
diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
index ed2e95d..72c6822 100644
--- a/arch/arm/include/asm/arch_timer.h
+++ b/arch/arm/include/asm/arch_timer.h
@@ -1,9 +1,12 @@
#ifndef __ASMARM_ARCH_TIMER_H
#define __ASMARM_ARCH_TIMER_H
+#include <linux/clocksource.h>
+
#ifdef CONFIG_ARM_ARCH_TIMER
int arch_timer_of_register(void);
int arch_timer_sched_clock_init(void);
+struct timecounter *arch_timer_get_timecounter(void);
#else
static inline int arch_timer_of_register(void)
{
@@ -14,6 +17,11 @@ static inline int arch_timer_sched_clock_init(void)
{
return -ENXIO;
}
+
+static inline struct timecounter *arch_timer_get_timecounter(void)
+{
+ return NULL;
+}
#endif
#endif
diff --git a/arch/arm/kernel/arch_timer.c b/arch/arm/kernel/arch_timer.c
index 54599e9..2b5da66 100644
--- a/arch/arm/kernel/arch_timer.c
+++ b/arch/arm/kernel/arch_timer.c
@@ -318,6 +318,15 @@ static cycle_t arch_counter_read(struct clocksource *cs)
return arch_counter_get_cntpct();
}
+static cycle_t arch_counter_read_cc(const struct cyclecounter *cc)
+{
+ /*
+ * Always use the physical counter for the clocksource.
+ * CNTHCTL.PL1PCTEN must be set to 1.
+ */
+ return arch_counter_get_cntpct();
+}
+
static struct clocksource clocksource_counter = {
.name = "arch_sys_counter",
.rating = 400,
@@ -326,6 +335,18 @@ static struct clocksource clocksource_counter = {
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
};
+static struct cyclecounter cyclecounter = {
+ .read = arch_counter_read_cc,
+ .mask = CLOCKSOURCE_MASK(56),
+};
+
+static struct timecounter timecounter;
+
+struct timecounter *arch_timer_get_timecounter(void)
+{
+ return &timecounter;
+}
+
static void __cpuinit arch_timer_stop(struct clock_event_device *clk)
{
int i;
@@ -376,6 +397,10 @@ static int __init arch_timer_register(void)
}
clocksource_register_hz(&clocksource_counter, arch_timer_rate);
+ cyclecounter.mult = clocksource_counter.mult;
+ cyclecounter.shift = clocksource_counter.shift;
+ timecounter_init(&timecounter, &cyclecounter,
+ arch_counter_get_cntpct());
for (i = PHYS_SECURE_PPI; i < MAX_TIMER_PPI; i++) {
irq_handler_t handler = arch_timer_handler;
--
1.7.10.3
