Re: [Xen-devel] [PATCH RFC 33/35] arm : acpi enable efi for acpi

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Jan,

On 11/02/2015 18:31, Jan Beulich wrote:
> > > > On 11.02.15 at 10:57, <julien.grall@xxxxxxxxxx> wrote:
> > Hi Ian,
> >
> > On 05/02/2015 20:05, Ian Campbell wrote:
> > > On Thu, 2015-02-05 at 11:58 +0000, Jan Beulich wrote:
> > > > > > > On 05.02.15 at 06:31, <julien.grall@xxxxxxxxxx> wrote:
> > > > > > --- a/xen/common/efi/runtime.c
> > > > > > +++ b/xen/common/efi/runtime.c
> > > > > > @@ -11,7 +11,13 @@ DEFINE_XEN_GUEST_HANDLE(CHAR16);
> > > > > >     #ifndef COMPAT
> > > > > >
> > > > > >     #ifdef CONFIG_ARM  /* Disabled until runtime services implemented */
> > > > > This comment seems irrelevant now.
> > > > >
> > > > > > +
> > > > > > +#if defined(CONFIG_ARM_64) && defined(CONFIG_ACPI)
> > > > > #ifdef CONFIG_ACPI
> > > > This is common code, and I can't see ACPI and EFI being always in the
> > > > same supported state (or else we could drop one of the two).
> > > EFI without ACPI is certainly a possibility on ARM64.
> > We would need to defined a new protocol in order to boot ACPI without EFI.
> >
> > Currently the ACPI fetch the rsdp pointer in 2 differents way depending
> > of efi_enabled:
> >         * efi_enabled == 1 => Use EFI to get the pointer
> >         * efi_enabled == 0 => Use the x86 legacy mode
> >
> > On ARM64, we have to use the first one.
> How that when not booting from EFI? Surely you can't use x86
> legacy mode, but if there is the possibility of ACPI without EFI
> (the opposite of what Ian indicated would be a possibility), then
> there ought to be another method to find RSDP on ARM too.
I should have been more clear on my previous mail. I didn't try to 
justify this patch (I think it's wrong too), but I wanted to expose our 
current use-case for ACPI.
We would, obviously, have to implement it when a new way to get ACPI is 
coming up. Currently, ACPI can only be retrieved via EFI on ARM64.
So if efi_enabled is not set, we should bail out rather than trying to 
use the legacy mode. It would help to support correctly ARM64 platform 
with only DT support (and not EFI).
Regards,

--
Julien Grall

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