[PATCH v7 04/17] ARM64 / ACPI: Introduce early_param for "acpi" and pass acpi=force to enable ACPI

[Parth Dixit]

On 21 January 2015 at 21:46, Catalin Marinas <catalin.marinas at 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:
>> >>>
>> >>> 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.
>>
>> 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?
>
>> >>> 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).
>>
>> 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