Re: [git pull] Input updates for 2.6.34-rc6

[Linus Torvalds <torvalds@linux-foundation.org>]

On Fri, 14 May 2010, Eric W. Biederman wrote:
> 
> efi_enabled is a guard on efi calls.  If it is true it tells you that
> you can make runtime efi calls.  If it is false you can't use runtime
> efi calls. efi_enabled does not tell you about the presence of efi
> on a system.

We don't really want to know about the "presense". What we want to know 
about is whether we were _loaded_ with EFI or not.

IOW, even if the system is EFI-capable, if we actually booted through the 
legacy BIOS interfaces, we would consider ourselves in "legacy" mode.

> All of which means in the normal case pay attention to acpi.  That is
> more likely to be correct and usable than EFI anything.

Oh yes. ACPI is actually _tested_, so while it's buggy, it's unlikely to 
be quite as spectacularly buggy as any EFI interfaces probably are.

But the issue here is that on a "legacy PC", we can't just say "ACPI 
doesn't mention this device, so it can't exist". Because in a legacy PC 
model, that simply isn't true. All those motherboard devices can easily 
exist (and do!) even if ACPI/PnP don't mention them.

But if we live in a non-legacy world (ie we were loaded through EFI), I 
think it's much more reasonable to say "we'll ignore any devices not 
mentioned by ACPI".

			Linus