Re: Design doc of adding ACPI support for arm64 on Xen - version 2

[Ian Campbell <ian.campbell@citrix.com>]

On Wed, 2015-08-12 at 13:11 +0100, Julien Grall wrote:
> On 12/08/15 12:23, Ian Campbell wrote:
> > Strictly it is considered a separate thing, much like loader.efi, despite
> > where it lives e.g. it is self contained and not allowed to call into the
> > kernel proper except via the formal interface provided for the hand-off.
> > 
> > That might seem like semantic quibbling, but I just want to clarify that
> > the Linux and BSD approaches here are basically the same.
> > 
> > Given that these device tree bindings are really just Linux's equivalent of
> > the "a format the kernel understands" which BSD uses as described above. I
> > don't know what format BSD uses, Linux just happened to have a DTB library
> > handy...
> 
> IIRC, on FreeBSD, the loader and the kernel is talking through a custom
> format called metadata. There is no modification of device tree by the
> loader.

Right, and as I say above Linux's equivalent of "a custom format called
metadata" is to declare a device tree binding.

> Although, I would prefer to see a common interface between Xen and DOM0
> rather than implementing a custom one for each OS we will support.

Agreed.

> I have to think how everything will work together. AFAIK, on x86, the
> loader is loading Xen and the FreeBSD kernel in the memory. The metadata
> necessary for the kernel is passed as a multiboot entry.
> 
> I will speak with Royger to see what we can do here.
> 
> In the meantime, I think we should drop "linux," when we standardize
> them to show that they are generic and not linux specific.

"we" here would be broader than just Xen of course.

Ian.