From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: [PATCH 1/3] rtc-efi: register rtc-efi device when EFI enabled Date: Fri, 28 Dec 2012 12:40:56 -0800 Message-ID: <50DE03D8.9030902@zytor.com> References: <1356712001-12198-1-git-send-email-jlee@suse.com> <3fa7337e-6bbc-4462-9704-2d8ac20a9cf2@email.android.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-efi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Matthew Garrett Cc: "Lee, Chun-Yi" , "matt.fleming-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "Lee, Chun-Yi" , Thomas Gleixner , Ingo Molnar , Jan Beulich , Len Brown , Arjan van de Ven List-Id: linux-efi@vger.kernel.org On 12/28/2012 11:17 AM, Matthew Garrett wrote: > On Fri, 2012-12-28 at 11:07 -0800, H. Peter Anvin wrote: >> We do have such machines, which is why this change has been reverted twice already. I believe we should stick to the priority scheme I proposed a few weeks ago. > > I seem to have missed that discussion, and couldn't find it after a > brief search. Got a pointer? > Looks like it was a non-public distribution ... anyway, what I wrote was: > I suspect that what we *should* do looks like: > > 1. If ACPI exports a Time and Alarm Device (ACPI000E) the use it; > 2. If ACPI exports an PC/AT device (PNP0B00/1/2) then use it(*); > 3. If we have an EFI RTC use it; > 4. Probe for a PC/AT RTC device. > > I'm unsure what the ordering of 1 & 2 should be. The ACPI device has > the advantage that it contains time zone information, which is important > for Windows interoperability, and at least optionally supports > millisecond resolution; there is no way to even export "this is where > you find time zone information" (since we're dealing with an RTC with > embedded CMOS, there is storage available, it is just a matter of > telling the OS how to find it) for the PNP0B0x devices. > > The TAD is also guaranteed to map 1:1 to the EFI RTC. > > -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754756Ab2L1Ulf (ORCPT ); Fri, 28 Dec 2012 15:41:35 -0500 Received: from terminus.zytor.com ([198.137.202.10]:38547 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754062Ab2L1Ulc (ORCPT ); Fri, 28 Dec 2012 15:41:32 -0500 Message-ID: <50DE03D8.9030902@zytor.com> Date: Fri, 28 Dec 2012 12:40:56 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: Matthew Garrett CC: "Lee, Chun-Yi" , "matt.fleming@intel.com" , "linux-kernel@vger.kernel.org" , "linux-efi@vger.kernel.org" , "Lee, Chun-Yi" , Thomas Gleixner , Ingo Molnar , Jan Beulich , Len Brown , Arjan van de Ven Subject: Re: [PATCH 1/3] rtc-efi: register rtc-efi device when EFI enabled References: <1356712001-12198-1-git-send-email-jlee@suse.com> <3fa7337e-6bbc-4462-9704-2d8ac20a9cf2@email.android.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/28/2012 11:17 AM, Matthew Garrett wrote: > On Fri, 2012-12-28 at 11:07 -0800, H. Peter Anvin wrote: >> We do have such machines, which is why this change has been reverted twice already. I believe we should stick to the priority scheme I proposed a few weeks ago. > > I seem to have missed that discussion, and couldn't find it after a > brief search. Got a pointer? > Looks like it was a non-public distribution ... anyway, what I wrote was: > I suspect that what we *should* do looks like: > > 1. If ACPI exports a Time and Alarm Device (ACPI000E) the use it; > 2. If ACPI exports an PC/AT device (PNP0B00/1/2) then use it(*); > 3. If we have an EFI RTC use it; > 4. Probe for a PC/AT RTC device. > > I'm unsure what the ordering of 1 & 2 should be. The ACPI device has > the advantage that it contains time zone information, which is important > for Windows interoperability, and at least optionally supports > millisecond resolution; there is no way to even export "this is where > you find time zone information" (since we're dealing with an RTC with > embedded CMOS, there is storage available, it is just a matter of > telling the OS how to find it) for the PNP0B0x devices. > > The TAD is also guaranteed to map 1:1 to the EFI RTC. > > -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.