From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: [RFC PATCH 06/14] rtc-efi: register rtc-efi device when EFI enabled Date: Fri, 20 Dec 2013 17:51:29 -0800 Message-ID: <52B4F421.2000403@zytor.com> References: <1387439515-8926-1-git-send-email-jlee@suse.com> <1387439515-8926-7-git-send-email-jlee@suse.com> <20131219140918.GF3145@console-pimps.org> <1387513491.3539.4345.camel@linux-s257.site> <52B3C7F8.3040901@zytor.com> <20131220103755.GA14784@pd.tnic> <1387552463.17961.2.camel@x230> <52B4B0ED.7030600@zytor.com> <1387589042.3539.4901.camel@linux-s257.site> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from terminus.zytor.com ([198.137.202.10]:50099 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752612Ab3LUBwl (ORCPT ); Fri, 20 Dec 2013 20:52:41 -0500 In-Reply-To: <1387589042.3539.4901.camel@linux-s257.site> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: joeyli Cc: Matthew Garrett , "bp@alien8.de" , "samer.el-haj-mahmoud@hp.com" , "linux-kernel@vger.kernel.org" , "tglx@linutronix.de" , "a.zummo@towertech.it" , "Elliott@hp.com" , "werner@suse.com" , "rtc-linux@googlegroups.com" , "x86@kernel.org" , "rjw@rjwysocki.net" , "mingo@redhat.com" , "oneukum@suse.de" , "linux-efi@vger.kernel.org" , "trenn@suse.de" , "matt.fleming@intel.com" , "JBeulich@suse.com" , "linux-acpi@vger.kernel.org" , "matt@console-pimps.org" On 12/20/2013 05:24 PM, joeyli wrote: > =E6=96=BC =E4=BA=94=EF=BC=8C2013-12-20 =E6=96=BC 13:04 -0800=EF=BC=8C= H. Peter Anvin =E6=8F=90=E5=88=B0=EF=BC=9A >> >> Actually, it doesn't have to reprogram the clock ... it just needs t= o >> 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. >> >=20 > 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 >=20 > and, > from Ted Ts'o in the mail thread > https://lkml.org/lkml/2008/1/8/195 >=20 > 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. >=20 > 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(). >=20 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 neve= r 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 -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html