linux-kernel - Re: [RFC PATCH 00/14] Support timezone of ACPI TAD and EFI TIME

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Message-ID: <2787644.ytU7M33B4r@vostro.rjw.lan>
Date:	Fri, 20 Dec 2013 22:45:11 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	joeyli <jlee@...e.com>, Alessandro Zummo <a.zummo@...ertech.it>,
	Matt Fleming <matt@...sole-pimps.org>,
	Matthew Garrett <matthew.garrett@...ula.com>, Elliott@...com,
	samer.el-haj-mahmoud@...com, Oliver Neukum <oneukum@...e.de>,
	werner@...e.com, trenn@...e.de, JBeulich@...e.com,
	linux-kernel@...r.kernel.org, rtc-linux@...glegroups.com,
	x86@...nel.org,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	linux-acpi@...r.kernel.org, Borislav Petkov <bp@...e.de>
Subject: Re: [RFC PATCH 00/14] Support timezone of ACPI TAD and EFI TIME

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

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