linux-kernel - Re: [PATCH 1/3] rtc-efi: register rtc-efi device when EFI enabled

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Message-ID: <50DE03D8.9030902@zytor.com>
Date:	Fri, 28 Dec 2012 12:40:56 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Matthew Garrett <matthew.garrett@...ula.com>
CC:	"Lee, Chun-Yi" <joeyli.kernel@...il.com>,
	"matt.fleming@...el.com" <matt.fleming@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"Lee, Chun-Yi" <jlee@...e.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Jan Beulich <JBeulich@...e.com>, Len Brown <lenb@...nel.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH 1/3] rtc-efi: register rtc-efi device when EFI enabled

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.

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