linux-kernel - Re: [RFC PATCH 06/14] rtc-efi: register rtc-efi device when EFI enabled

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Date:	Sat, 21 Dec 2013 23:34:08 +0800
From:	joeyli <jlee@...e.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Matthew Garrett <matthew.garrett@...ula.com>,
	"bp@...en8.de" <bp@...en8.de>,
	"samer.el-haj-mahmoud@...com" <samer.el-haj-mahmoud@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"a.zummo@...ertech.it" <a.zummo@...ertech.it>,
	"Elliott@...com" <Elliott@...com>,
	"werner@...e.com" <werner@...e.com>,
	"rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"oneukum@...e.de" <oneukum@...e.de>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"trenn@...e.de" <trenn@...e.de>,
	"matt.fleming@...el.com" <matt.fleming@...el.com>,
	"JBeulich@...e.com" <JBeulich@...e.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"matt@...sole-pimps.org" <matt@...sole-pimps.org>
Subject: Re: [RFC PATCH 06/14] rtc-efi: register rtc-efi device when EFI
 enabled

於 五，2013-12-20 於 17:51 -0800，H. Peter Anvin 提到：
> On 12/20/2013 05:24 PM, joeyli wrote:
> > 於 五，2013-12-20 於 13:04 -0800，H. Peter Anvin 提到：
> >>
> >> Actually, it doesn't have to reprogram the clock ... it just needs to
> >> know if another OS has already done so.  All Linux needs to do is to be
> >> able to derive UTC from whatever the RTC is set to and to be able to
> >> keep it consistent.
> >>
> > 
> > It's dependent on a right boot initial priority of distribution.
> 
> -ENOPARSE
> 
> > Here have a discussion of adjusting system clock by TZ (from ACPI or
> > UEFI):
> > Discussion on BIOS/CMOS/UEFI clock in local time
> > 	http://www.spinics.net/lists/util-linux-ng/msg07639.html
> > 
> > and,
> > from Ted Ts'o in the mail thread
> >      https://lkml.org/lkml/2008/1/8/195
> > 
> > If kernel use the TZ field from ACPI TAD or EFI to adjust system
> > clock when booting, then it can avoid buggy distributions adjust
> > system clock AFTER e2fsck is run.
> > 
> > Using ACPI TAD should after DSDT parsing in subsystem initial stage,
> > so I choice EFI time services before we can move DSDT parser to
> > start_kernel().
> > 
> 
> Yes, of course.  That is irrelevant to needing to reprogram the clock,
> though.
> 
> My argument is very simple: if we have to rely on EFI, we can get the
> offset in the boot stub before ExitBootServices(), and then simply never
> change it.  That way we still pick up if another operating system has
> changed it, and it will still reflect the proper UTC time.
> 
> 	-hpa
> 

OK, I will add this part to next version for the UEFI system doesn't
have ACPI TAD.


Thanks for your suggestion!
Joey Lee

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