linux-kernel - Re: [Xen-devel] [PATCH 3/3] x86/xen: sync the CMOS RTC as well as the Xen wallclock

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Date:	Wed, 15 May 2013 09:19:42 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"David Vrabel" <david.vrabel@...rix.com>,
	"John Stultz" <john.stultz@...aro.org>
Cc:	"Thomas Gleixner" <tglx@...utronix.de>, <xen-devel@...ts.xen.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 3/3] x86/xen: sync the CMOS RTC as well
 as the Xen wallclock

>>> On 14.05.13 at 19:24, John Stultz <john.stultz@...aro.org> wrote:
> On 05/13/2013 10:56 AM, David Vrabel wrote:
>> From: David Vrabel <david.vrabel@...rix.com>
>>
>> If NTP is used in dom0 and it is synchronized to its clock source,
>> then the kernel will periodically synchronize the Xen wallclock with
>> the system time.  Updates to the Xen wallclock do not persist across
>> reboots, so also synchronize the CMOS RTC (as on bare metal).
>>
>> Signed-off-by: David Vrabel <david.vrabel@...rix.com>
>> ---
>>   arch/x86/xen/time.c |   11 ++++++++++-
>>   1 files changed, 10 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
>> index a1947ac..4656165 100644
>> --- a/arch/x86/xen/time.c
>> +++ b/arch/x86/xen/time.c
>> @@ -14,6 +14,7 @@
>>   #include <linux/kernel_stat.h>
>>   #include <linux/math64.h>
>>   #include <linux/gfp.h>
>> +#include <linux/mc146818rtc.h>
>>   
>>   #include <asm/pvclock.h>
>>   #include <asm/xen/hypervisor.h>
>> @@ -199,17 +200,25 @@ static void xen_get_wallclock(struct timespec *now)
>>   static int xen_set_wallclock(const struct timespec *now)
>>   {
>>   	struct xen_platform_op op;
>> +	int ret;
>>   
>>   	/* do nothing for domU */
>>   	if (!xen_initial_domain())
>>   		return -1;
>>   
>> +	/* Set the Xen wallclock. */
>>   	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);
>> +	ret = HYPERVISOR_dom0_op(&op);
>> +	if (ret)
>> +		return ret;
>> +
>> +	/* Set the hardware RTC. */
>> +	return mach_set_rtc_mmss(now);
> 
> Sorry, just noticed one more thing while applying this. Do all Xen 
> systems run on hardware that has the conventional CMOS clock?
> 
> What happens if the bare-metal needs to use efi_set_rtc() or 
> vrtc_set_mmss() ?

There's no EFI support in the upstream kernel yet when running
on Xen (the code that's in the kernel can't be used, as Dom0
can't directly invoke EFI runtime service functions).

And I don't think Xen is in any way prepared to run on
Moorestown, which afaict is where vrtc_set_mmss() comes into
the picture.

Jan

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