[PATCH v3 5/6] xen/arm: introduce xen_read_wallclock

Stefano Stabellini
2015-11-11T16:51:35Z

Read the wallclock from the shared info page at boot time.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

---

Changes in v3:
- use ktime_get_ns instead of calling into the arch_timer functions
directly
- read the wallclock from the late_initcall

Changes in v2:
- properly convert arch_timer ticker to nsec
- use timespec64 interfaces
- use sec_hi to get a 64-bit seconds value
---
arch/arm/xen/enlighten.c | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 2f57ba3..eede8e9 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -28,6 +28,7 @@
#include <linux/cpufreq.h>
#include <linux/cpu.h>
#include <linux/console.h>
+#include <linux/timekeeping.h>

#include <linux/mm.h>

@@ -95,6 +96,30 @@ static unsigned long long xen_stolen_accounting(int cpu)
return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline];
}

+static void xen_read_wallclock(struct timespec64 *ts)
+{
+ u32 version;
+ u64 delta;
+ struct timespec64 now;
+ struct shared_info *s = HYPERVISOR_shared_info;
+ struct pvclock_wall_clock *wall_clock = &(s->wc);
+
+ /* get wallclock at system boot */
+ do {
+ version = wall_clock->version;
+ rmb(); /* fetch version before time */
+ now.tv_sec = ((uint64_t)wall_clock->sec_hi << 32) | wall_clock->sec;
+ now.tv_nsec = wall_clock->nsec;
+ rmb(); /* fetch time before checking version */
+ } while ((wall_clock->version & 1) || (version != wall_clock->version));
+
+ /* time since system boot */
+ delta = ktime_get_ns();
+ delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
+
+ *ts = ns_to_timespec64(delta);
+}
+
static void xen_percpu_init(void)
{
struct vcpu_register_vcpu_info info;
@@ -303,6 +328,11 @@ static int __init xen_pm_init(void)

pm_power_off = xen_power_off;
arm_pm_restart = xen_restart;
+ if (!xen_initial_domain()) {
+ struct timespec64 ts;
+ xen_read_wallclock(&ts);
+ do_settimeofday64(&ts);
+ }

return 0;
}
--
1.7.10.4