Re: [Xen-devel] [PATCH] x86: Don't honour ACPI indicating absence of CMOS RTC

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.06.14 at 17:47, <konrad.wilk@xxxxxxxxxx> wrote:
> On Tue, Jun 17, 2014 at 04:12:32PM +0100, Jan Beulich wrote:
>> >>> On 17.06.14 at 16:58, <andrew.cooper3@xxxxxxxxxx> wrote:
>> > This reverts f74556693 "x86: honor ACPI indicating absence of CMOS RTC"
>> > 
>> > Certain HP Gen8 BIOSes have started setting this bit despite an RTC CMOS 
>> > being present and working.
>> > 
>> > Their reasonsing is to prevent EFI-booted OSes from playing with the CMOS,
>> > combined with the erroneous assumption that the only OSes using legacy boot
>> > are too old to know about ACPI v5 and therefore to understand this bit.
>> 
>> Which implies you can boot from EFI on those systems, which is
>> precisely what the panic message says you ought to do. Why do
>> you not boot via EFI in the first place?
> 
> You can swap between legacy and EFI in the BIOS. Customers can choose
> either option.

I know on many systems you still can, but the question is "Why would
you?" In particular when you know the firmware is assuming that the
CSM is only being used by old OSes.

Jan


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