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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.06.14 at 15:06, <konrad.wilk@xxxxxxxxxx> wrote:
> On Wed, Jun 18, 2014 at 01:00:23PM +0100, Jan Beulich wrote:
>> >>> On 17.06.14 at 18:31, <konrad.wilk@xxxxxxxxxx> wrote:
>> > On Tue, Jun 17, 2014 at 05:01:12PM +0100, Jan Beulich wrote:
>> >> >>> 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.
>> > 
>> > PCIe devices that don't EFI for setting up.
>> 
>> I'm sorry, but I don't understand what you're trying to tell me.
> 
> Some of the PCIe devices have an GUI/text which you can invoke during
> bootup. For example LSI or Adaptec allow one to hit Ctrl-C to get a menu
> to setup RAID and such.
> 
> But for that to work in EFI (and when the BIOS is using the EFI framebuffer)
> that firmware has to use the EFI to setup the windows and such. Some of
> those cards don't have it and will not show said menus at all. Hence
> users stick with Legacy so they can administer those cards as they
> see fit.

At least from an abstract perspective these are different things: When
CSM is still there, UEFI can very well run the legacy option ROM init code,
and then nevertheless boot the OS from UEFI. Plus the setting up of
RAID and such doesn't need to be done before every OS boot - you'd
do that once, reset the box (if necessary), and boot your OS from UEFI.

Jan


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