On 21 January 2015 at 21:46, Catalin Marinas <catalin.marinas@xxxxxxx> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
