On Wed, Jan 21, 2015 at 03:42:43PM +0000, Catalin Marinas wrote:

On Wed, Jan 21, 2015 at 03:29:52PM +0000, Jon Masters wrote:

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On 01/21/2015 10:23 AM, Catalin Marinas wrote:

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I have some questions for the ACPI and EFI folk:

1. When booting with ACPI, are the EFI run-time services required for
   anything? If yes, Xen may have a bigger problem

Yes. At least for some things. For example, installing an Operating
System would require that you make runtime services calls to set the
BootOrder/BootNext variables, and so on. Further, we use the GetTime
service and EFI based reboot to avoid having special drivers. I had
those added to SBBR as requirements for that reason.

So what would a kexec'ed kernel do here? Or we usually expect it to be
short lived and doesn't need reboot, nor GetTime.

Xen is slightly more problematic but I wonder whether it could run a
(paravirtualised) UEFI.

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2. Could a boot loader (either kernel doing kexec or Xen) emulate the
   EFI system/config tables and still make them useful to the kernel but
   without EFI_BOOT or EFI_RUNTIME_SERVICES?

Yes. But again, without the other required pieces (including the
services function pointers in the systab which are required) you'd crash
soon after boot trying to make those calls.

My point was whether you can still pass information like RSDP address
via EFI tables but explicitly disable runtime services so that the
kernel won't try to make such calls (and crash).

There is no specific dependency from ACPI->EFI its just the only current
method defind to get the RSDP pointer. It would work just as well
getting the pointer from /chosen/ if we just pick a node and document it
for Xen/kexec/other usage.

We were running ACPI on machine from u-boot doing exactly this for
a long time.

Graeme