Re: [Xen-devel] [PATCH RFC] efi: By default use the BOOT_ACPI method instead of BOOT_EFI unless on reduced ACPI hardware.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.01.15 at 16:01, <konrad.wilk@xxxxxxxxxx> wrote:
> On Thu, Jan 22, 2015 at 09:49:08AM +0000, Jan Beulich wrote:
>> >>> On 21.01.15 at 22:53, <konrad.wilk@xxxxxxxxxx> wrote:
>> > This mimics the behavior of the Linux kernel in which the reboot
>> > sequence by default under EFI booted kernels is first ACPI.
>> 
>> Which is contrary to the EFI spec. I.e. NAK.
> 
> I am failing to see that in the spec. I see that it says what
> the ResetSystem() call does, but nothing about "MUST".
> 
> I see this at the start of the spec:
> 
> " Together, these provide a standard environment for booting an OS. This
> specification is designed as a pure interface specification. As such,
> the specification defines the set of interface s and structures that
> platform firmware must implement. "
> 
> (which talks about 'booting an OS' - which this is not, and interestingly
> enough - it does say implement, but not where it must implement it
> correctly!).
> 
> But I have not dug that deep in the spec to find something
> that says you MUST not use existing other specs? Perhaps you
> remember where the contrary part is?

The whole spirit of EFI is to get the OS away from doing things
some custom (and hence possibly fragile) way.

> Also, why do we want to be different that Windows and Linux when doing
> EFI operations?

Because just because they do things a certain way doesn't mean
they do it right. Linux having actively removed using the time
related runtime services functions is something that I for example
absolutely can't agree with. If there are firmware vendors not
getting their act together, having ways to work around that is
acceptable, but outright violation of the spec is wrong imo.

>> > EFI reboot is only tried if the user supplied it or if the hardware
>> > is an ACPI 5.0 (or higher) reduced hardware board.
>> > 
>> > This fixes the EFI firmware crashing on Lenovo ThinkCentre M57
>> 
>> Buggy firmware should be worked around with "reboot="; I'd
>> certainly accept a patch to bypass efi_reset_system() in that
>> case.
> 
> Independent of the conversation above I will work the patch
> that way.  Would you also be OK if I stuck the DMI data for the
> ThinkCentre to make this automatic?

Yes, as long as the match isn't too generic (i.e. wouldn't match all
furure models too).

Jan


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