Re: [Xen-devel] [PATCH v7 2/3] * util/grub.d/20_linux_xen.in: Add xen_boot command support for aarch64

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 3 May 2017, Andrew Cooper wrote:
> On 02/05/17 08:06, fu.wei@xxxxxxxxxx wrote:
> > From: Fu Wei <fu.wei@xxxxxxxxxx>
> >
> > This patch adds the support of xen_boot command for aarch64:
> >     xen_hypervisor
> >     xen_module
> > These two commands are only for aarch64, since it has its own protocol and
> > commands to boot xen hypervisor and Dom0, but not multiboot.
> >
> > For other architectures, they are still using multiboot and module
> > commands.
> >
> > Signed-off-by: Fu Wei <fu.wei@xxxxxxxxxx>
> 
> Sorry if I am jumping in late and asking awkward questions, but what is
> special about Xen/aarch64 here?  Why is it using a non-standard entry
> mechanism?

Multiboot is not available on ARM. The boot protocol we have on ARM is
FDT based:

http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=docs/misc/arm/device-tree/booting.txt

We often refer to it as "multiboot for arm" but in fact it is not
related to the x86 multiboot in any way.

In Grub, the two protocols (multiboot and
docs/misc/arm/device-tree/booting.txt) are kept clearly distinct
(55A687E5.4070106@xxxxxxxxx). Hence, the need for this patch.

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