linux-kernel - Re: [PATCH 1/2] UEFI arm64: add noefi boot param

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Date:	Wed, 6 Aug 2014 14:29:41 +0100
From:	Leif Lindholm <leif.lindholm@...aro.org>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	Dave Young <dyoung@...hat.com>, catalin.marinas@....com,
	will.deacon@....com, matt.fleming@...el.com,
	ard.biesheuvel@...aro.org, msalter@...hat.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-efi@...r.kernel.org
Subject: Re: [PATCH 1/2] UEFI arm64: add noefi boot param

On Wed, Aug 06, 2014 at 02:20:21PM +0100, Matt Fleming wrote:
> > Since this is really turning an x86-specific feature into a generic
> > one, could it be moved to core code?
> > Maybe an efi.mask, reusing the efi_enabled defines, with an
> > efi_disabled macro?
>  
> Why the new efi_disabled() and efi.mask? This is all achievable with
> efi_enabled() and efi.flags, in fact, this kind of thing is exactly why
> they were invented.

Because this flag is indicating which facilities we should not try to
enable, rather than which facilities we have enabled.

The EFI_RUNTIME_SERVICES flag is set after successful call to
set_virtual_address_map. The apparent intent of "noefi" is to prevent
that call from being made in the first place.

Anyway, it was just a suggestion - main point was it would make sense
to share the code.
 
> > Also, since this patch (and its x86 predecessor) is not really
> > "noefi", could this be integrated with the "efi=" patch
> > (http://permalink.gmane.org/gmane.linux.kernel.efi/4405),
> > as an efi=noruntime option?
> > 
> > On x86, due to CSM, "noefi" was a useful fallback for completely
> > broken (U)EFI implementations - but on an arm* UEFI system, there will
> > be no fallback. Could it be wrapped in a kernel hacking config option?
>  
> I don't mind making "noefi" a synonym for "efi=noruntime" on x86, as
> long as we keep "noefi" around with the same semantics it's always had.

Yeah, that would be nice.

/
    Leif
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