On 21 January 2015 at 21:46, Catalin Marinas catalin.marinas@arm.com wrote:
On Wed, Jan 21, 2015 at 04:05:33PM +0000, Jon Masters wrote:
On 01/21/2015 10:42 AM, Catalin Marinas wrote:
On Wed, Jan 21, 2015 at 03:29:52PM +0000, Jon Masters wrote:
On 01/21/2015 10:23 AM, Catalin Marinas wrote:
I have some questions for the ACPI and EFI folk:
- 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.
In the use case that I have, it'll use EFI Runtime Servies to handle both the time of day (which it will need) and to subsequently reboot. This is currently being worked on (integration into kdump).
So the EFI run-time services (and EFI tables) will be preserved across kexec? Could Xen not to something similar?
- 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).
Yes. As Graeme says, it works just to pass in the ACPI information and turn off EFI *BUT* it does not work to say you have EFI and then not provide the correct EFI services. To do so is out of spec, and in fact it's one reason we weren't able to turn the GetTime service on generally for x86 - some older x86 boxes didn't implement it originally (another reason on our end we're requiring all of these services on day one so that there won't be time for someone to miss them in firmware).
This is the use case i am talking about, we have a wroking setup with efi disabled and rsdp passed via dtb, right now its done by adding a "rsdp" field in the chosen node. Do we have a formal way to pass RSDP without EFI? if not, it would be good to have dtb binding which we can use to pass RSDP address to kernel for ACPI.
OK, thanks for confirming this. So the answer to my second question is "not really".
-- Catalin