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

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Message-ID: <m1aas2kjb6.fsf@fess.ebiederm.org>
Date:	Fri, 14 May 2010 00:56:45 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-input@...r.kernel.org, Bastien Nocera <hadess@...ess.net>
Subject: Re: [git pull] Input updates for 2.6.34-rc6

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Thu, 13 May 2010, Dmitry Torokhov wrote:
>> 
>> Is there an interface a driver can use to query the style of boot used?
>
> Maybe 'efi_enabled' will do. I haven't checked exact semantics of that 
> flag. And right now we don't even know if Bastien even uses EFI, or boots 
> a traditional kernel image through bootcamp.

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.

efi_enabled is generally uninteresting because there is an agreement
that you should be able to all of the runtime work that matters with
acpi.

This is reinforced by the fact that efi comes in two different flavors
on x86 32bit and 64bit, and 64bit efi does not have a 32bit
compatibility layer (too many hard coded pointers in the interface).
You can't make 32bit efi calls from from a 64bit kernel or 64bit efi
calls from a 32bit kernel.

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

Eric
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