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Date: Wed, 12 Nov 2014 12:04:19 +0000
From: Mark Rutland <mark.rutland@arm.com>
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Subject: Re: [Qemu-devel] [Linaro-acpi] [RFC PATCH 0/7] hw/arm/virt: Dynamic
 ACPI v5.1 table generation
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, "Ian.Campbell@citrix.com" <Ian.Campbell@citrix.com>, "linaro-acpi@lists.linaro.org" <linaro-acpi@lists.linaro.org>, Alexander Spyridakis <a.spyridakis@virtualopensystems.com>, Julien Grall <julien.grall@linaro.org>, Claudio Fontana <claudio.fontana@huawei.com>, QEMU Developers <qemu-devel@nongnu.org>, Leif Lindholm <leif.lindholm@linaro.org>, "stefano.stabellini@citrix.com" <stefano.stabellini@citrix.com>, "grant.likely@linaro.org" <grant.likely@linaro.org>, "tech@virtualopensystems.com" <tech@virtualopensystems.com>, Parth Dixit <parth.dixit@linaro.org>, Christoffer Dall <christoffer.dall@linaro.org>

On Wed, Nov 12, 2014 at 11:52:22AM +0000, Paolo Bonzini wrote:
> 
> On 12/11/2014 11:38, Mark Rutland wrote:
> > > I share your concern, but running another UEFI instance for Dom0 doesn't
> > > seem like a viable alternative either.  Why is this a problem on ARM and
> > > not on x86 though?
> > 
> > I believe that on x86 the fallback for !UEFI would be the e820 memory
> > map, which provides info regarding the type of the memory mapping, as
> > opposed to just the base + size. That said, I'm not that familiar with
> > e820, and from a quick look the provided information doesn't seem to be
> > that detailed.
> 
> The e820 memory map is only part of it.  On x86 !UEFI you are supposed
> to scan low memory for magic signatures that provides pointers to the
> SMBIOS and ACPI tables.

Fun...

> As Christoffer said, "the good old PC". :)
> 
> SeaBIOS fishes out information from fw_cfg, and puts it in low memory.
> On ARM you could use DT binary blobs instead of fw_cfg, as proposed
> already (I don't remember if it was in this thread or IRC).  Then if you
> want to go !UEFI you can extract the tables from those binary blobs.

This sounds broken. I am very much not a fan of shoving binary blobs
into DT to workaround a shoddy boot interface.

Mark.