Re: [Qemu-devel] [Linaro-acpi] [RFC PATCH 0/7] hw/arm/virt: Dynamic ACPI v5.1 table generation

[Christoffer Dall <christoffer.dall@linaro.org>]

On Tue, Nov 11, 2014 at 03:29:33PM +0000, Mark Rutland wrote:
> Hi,
> 
> On Thu, Nov 06, 2014 at 01:33:20PM +0000, Alexander Spyridakis wrote:
> > On 6 November 2014 14:44, Peter Maydell <peter.maydell@linaro.org> wrote:
> > >
> > >
> > > > We need ACPI guest support in QEMU for AArch64 over here, with all features
> > > > (including the ability to run ACPI code and add specific tables), for
> > > > ACPI-based guests.
> > >
> > > The plan for providing ACPI to guests is that we run a UEFI BIOS
> > > blob which is what is responsible for providing ACPI and UEFI
> > > runtime services to guests which need them. (The UEFI blob finds
> > > out about its hardware by looking at a device tree that QEMU
> > > passes it, but that's a detail between QEMU and its bios blob).
> > > This pretty much looks like what x86 QEMU used to do with ACPI
> > > for a very long time, so we know it's a feasible approach.
> > 
> > Hi Peter,
> > 
> > The rational in the proposed approach is meant for cases where the
> > user does not want to rely on external firmware layers. While UEFI
> > could do what you are describing, the point is to avoid this not so
> > trivial overhead in the booting process. Especially in the case of
> > thin guests, where another software dependency is undesired.
> 
> I'm not sure how you plan to use ACPI without UEFI, as there are several
> pieces of information which ACPI misses, such as the memory map, which
> must be discovered from UEFI. How do you intend to discover the memory
> map without UEFI?
> 
> Additionally, with Linux and other generic OSs, the expectation is that
> the ACPI tables are discovered via the UEFI system table. How do you
> intend to discover the ACPI tables? Or other system information?

FWIW, Xen needs to pass the RDSP pointer along with a tiny DT containing
the command line and memory information to Dom0 as well.  We are
currently suggesting adding an RDSP property to the chosen node in the
tiny DT, but a command-line arguement like kexec proposed could be
another option I guess, albeit not a very pretty one.

But, what I hear from Huawei is that they don't want any DT and don't
want any UEFI, so not sure how they plan on accomplishing that.

-Christoffer