[PATCH 2/2] x86/xen: sync the CMOS RTC as well as the Xen wallclock

[David Vrabel <david.vrabel@citrix.com>]

From: David Vrabel <david.vrabel@citrix.com>

Adjustments to Xen's persistent_clock via update_persistent_clock()
don't actually persist, as the Xen wallclock is just used by domU
guests, and modifications to it do not modify the underlying CMOS RTC.

The x86_platform.set_wallclock hook can be used to keep the hardware
RTC synchronized (as on bare metal).  Because the Xen wallclock is now
kept synchronized by xen_pvclock_gtod_notify() on any system time
change, xen_set_wallclock() need not do this and dom0 can simply use
the native implementation.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
 arch/x86/xen/time.c |   17 ++++-------------
 1 files changed, 4 insertions(+), 13 deletions(-)

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 60b7d1f..0e69994 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -199,18 +199,7 @@ static void xen_get_wallclock(struct timespec *now)
 
 static int xen_set_wallclock(const struct timespec *now)
 {
-	struct xen_platform_op op;
-
-	/* do nothing for domU */
-	if (!xen_initial_domain())
-		return -1;
-
-	op.cmd = XENPF_settime;
-	op.u.settime.secs = now->tv_sec;
-	op.u.settime.nsecs = now->tv_nsec;
-	op.u.settime.system_time = xen_clocksource_read();
-
-	return HYPERVISOR_dom0_op(&op);
+	return -1;
 }
 
 static int xen_pvclock_gtod_notify(struct notifier_block *nb, unsigned long unused,
@@ -531,7 +520,9 @@ void __init xen_init_time_ops(void)
 
 	x86_platform.calibrate_tsc = xen_tsc_khz;
 	x86_platform.get_wallclock = xen_get_wallclock;
-	x86_platform.set_wallclock = xen_set_wallclock;
+	/* Dom0 uses the native method to set the hardware RTC. */
+	if (!xen_initial_domain())
+		x86_platform.set_wallclock = xen_set_wallclock;
 }
 
 #ifdef CONFIG_XEN_PVHVM
-- 
1.7.2.5