Re: [PATCH 1/3] rtc-efi: register rtc-efi device when EFI enabled
From: Matt Fleming
Date: Wed Jan 02 2013 - 02:26:28 EST
On Wed, 2013-01-02 at 10:45 +0800, joeyli wrote:
> I didn't find the EFI RTC problem on Asus from google.
> Could you please share what's the situation on ASUS hardware?
It's mentioned in the following commit (which has since been reverted in
Author: Matt Fleming <matt.fleming@xxxxxxxxx>
Date: Fri Sep 7 18:28:04 2012 +0100
x86, efi: 1:1 pagetable mapping for virtual EFI calls
Some firmware still needs a 1:1 (virt->phys) mapping even after we've
called SetVirtualAddressMap(). So install the mapping alongside our
existing kernel mapping whenever we make EFI calls in virtual mode.
This bug was discovered on ASUS machines where the firmware
implementation of GetTime() accesses the RTC device via physical
addresses, even though that's bogus per the UEFI spec since we've
informed the firmware via SetVirtualAddressMap() that the boottime
memory map is no longer valid.
This bug seems to be present in a lot of consumer devices, so there's
not a lot we can do about this spec violation apart from workaround
The bug was originally mentioned here,
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