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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: joeyli <jlee@suse.com>, Alessandro Zummo <a.zummo@towertech.it>,
        Matt Fleming <matt@console-pimps.org>,
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        "linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
        linux-acpi@vger.kernel.org, Borislav Petkov <bp@suse.de>
Subject: Re: [RFC PATCH 00/14] Support timezone of ACPI TAD and EFI TIME
Date: Fri, 20 Dec 2013 22:45:11 +0100
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On Friday, December 20, 2013 01:10:26 PM H. Peter Anvin wrote:
> On 12/19/2013 09:38 PM, joeyli wrote:
> > 
> > If don't use EFI time, then the first priority is using ACPI TAD if it
> > present. Due to ACPI TAD is a generic acpi device that's need OS parsing
> > DSDT table before set system time.
> > 
> > Either move DSDT parser from subsystem initial stage to start_kernel or
> > move timekeeping initial to after DSDT be parsed. Which one you think is
> > more possible and risk less? Then I will try that way.
> > 
> 
> I discussed the DSDT/SSDT parsing issue with Rafael and he claims it
> would require a lot of restructuring.  Unfortunately ACPI is at this
> point done rather late, as I understand.  All of this is a big problem.

My understanding, however, is that to use the TAD, we don't actually need to
create a struct acpi_device for it.  We just need a handle to the ACPICA
object which can be found using acpi_get_devices() as soon as the namespace
has been extracted from the DSDT and friends.  That in turn happens in
acpi_early_init(), which is called from start_kernel() right before
efi_late_init().

Is that early enough?

Rafael