On 29 January 2015 at 15:19, Catalin Marinas <catalin.marinas@xxxxxxx> wrote: > On Wed, Jan 28, 2015 at 06:18:44PM +0000, Timur Tabi wrote: >> On 01/28/2015 12:14 PM, Catalin Marinas wrote: >> >> >So it looks like there's a whole conversation about this already in >> >> >this thread that I didn't notice. However, reading through all of it, >> >> >I still don't understand sure why the presence of ACPI tables is >> >> >insufficient to enable ACPI. >> >> > Because ACPI on arm64 is still experimental, no matter how many people >> > claim that it is production ready in their private setups. >> >> Fair enough. Does this mean that passing "acpi=force" on the kernel >> command line is a requirement for ARM64 servers? > > Please read my other email and ideally the whole sub-thread. The > acpi=force should only be required if the SoC is described (from > firmware) by both DT and ACPI. > >> >> >In what situation would we want to ignore ACPI tables that are >> >> >present? >> >> > When DT tables are also present (and for the first platforms, that's >> > highly recommended, though not easily enforceable at the kernel level). >> >> My understanding is that the EFI stub creates a device tree (and it >> contains some important information), so I don't understand how we can >> ever have an ACPI-only platform on ARM64 servers. > > If EFI stub creates the DT itself (not passed by firmware), it will > write some information in the chosen node that the rest of the kernel > can make use of and take the appropriate decision on whether to use ACPI > or not. That's something that will be used by kexec and Xen as well > which may want to boot with ACPI tables outside an EFI environment. > If we are going with this solution, we should also mandate that an ACPI enabled firmware should not supply a non-DT DTB, or we wouldn't spot the difference. Not sure how likely this is, but I could imagine a firmware setting up an initrd and hence populating the /chosen node in an otherwise empty DTB. In this case, the stub would not add its 'I-created-an-empty-dtb' property. -- Ard. -- 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
