linux-kernel - Re: [PATCH v2 2/3] arm: Add [U]EFI runtime services support

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Date:	Thu, 17 Oct 2013 16:31:21 +0200
From:	Leif Lindholm <leif.lindholm@...aro.org>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org, matt.fleming@...el.com,
	grant.likely@...retlab.ca, roy.franz@...aro.org, msalter@...hat.com
Subject: Re: [PATCH v2 2/3] arm: Add [U]EFI runtime services support

On Thu, Oct 17, 2013 at 03:07:39PM +0100, Matt Fleming wrote:
> > +/*
> > + * If you need to (temporarily) support buggy firmware.
> > + */
> > +#define KEEP_BOOT_SERVICES_REGIONS
> 
> Have you seen firmware that requires this? I'm just curious more than
> anything else.

Not really.
I _think_ I saw it on a debug build of a development platform once.
That coincided with me seeing a post on linux-efi about some laptop
that broke unless boot services regions were preserved, so I decided
to put it in there for any future debugging.
 
> > +/*
> > + * Returns 1 if 'facility' is enabled, 0 otherwise.
> > + */
> > +int efi_enabled(int facility)
> > +{
> > +	return test_bit(facility, &arm_efi_facility) != 0;
> > +}
> > +EXPORT_SYMBOL(efi_enabled);
> 
> This should move to drivers/firmware/efi/efi.c. Let me write a patch
> that moves the x86 stuff out of arch/x86 and means you can get rid of
> this hunk.
 
Excellent, thanks!

> > +/*
> > + * Called explicitly from init/mm.c
> > + */
> 
> That's init/main.c.
 
*cough*, right.

> > +void __init efi_enter_virtual_mode(void)
> > +{
> > +	efi_status_t status;
> > +
> > +	if (!efi_enabled(EFI_BOOT)) {
> > +		pr_info("EFI services will not be available.\n");
> > +		return;
> 
> This is dead code as PATCH 3 does,
> 
> diff --git a/init/main.c b/init/main.c
> index af310af..ec6d76e 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -875,6 +875,10 @@ static noinline void __init
> kernel_init_freeable(void)
> 	smp_prepare_cpus(setup_max_cpus);
> 
> 	do_pre_smp_initcalls();
> +
> +	if (IS_ENABLED(CONFIG_ARM) && efi_enabled(EFI_BOOT))
> +		efi_enter_virtual_mode();
> +

True.

However, this call site is likely to change in the future (preferably
to an early_initcall), if we redesign the memory mapping to be reusable
after kexec(). At which point the test in efi_enter_virtual_mode() will
make sense again.

Could I change the test in init/main.c to do
     if (IS_ENABLED(CONFIG_ARM) && IS_ENABLED(CONFIG_EFI))
instead?

/
    Leif
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