On Tuesday, August 12, 2014 07:23:47 PM Catalin Marinas wrote:

On Mon, Jul 28, 2014 at 07:27:52PM +0100, Olof Johansson wrote:

quoted

On Mon, Jul 28, 2014 at 10:00 AM, Mark Rutland [off-list ref] wrote:

quoted

On Mon, Jul 28, 2014 at 05:27:50PM +0100, Olof Johansson wrote:

quoted

On Mon, Jul 28, 2014 at 11:07:50AM +0200, Arnd Bergmann wrote:

quoted

On Saturday 26 July 2014 19:34:48 Olof Johansson wrote:

quoted

On Thu, Jul 24, 2014 at 6:00 AM, Hanjun Guo [off-list ref] wrote:

quoted

+Relationship with Device Tree
+-----------------------------
+
+ACPI support in drivers and subsystems for ARMv8 should never be mutually
+exclusive with DT support at compile time.
+
+At boot time the kernel will only use one description method depending on
+parameters passed from the bootloader.

Possibly overriden by kernel bootargs. And as debated for quite a
while earlier this year, acpi should still default to off -- if a DT
and ACPI are both passed in, DT should at this time be given priority.

I think this would be harder to do with the way that ACPI is passed in
to the kernel. IIRC, you always have a minimal DT information based on
the ARM64 boot protocol, but in the case of ACPI, this contains pointers
to the ACPI tables, which are then used for populating the Linux platform
devices (unless acpi=disabled is set), while the other contents of the
DTB may be present but we skip the of_platform_populate state.

How can it be harder to do? If you support acpi=off, then you should support
acpi=on.

Another alternative would be to have an early fixup that stubs out
the acpi properties from the DTB unless there's an 'acpi' or 'acpi=on'
argument on the cmdline. Not quite as tidy a solution, though.

I don't follow:

If you want to disable ACPI, you can pass acpi=off. This is your
workaround for broken ACPI (and only if you happen to have wrirten your
own DTB, because many/most ACPI systems WILL NOT have a DTB to begin
with).

All ACPI should be assumed broken at this time, so acpi=off _must_ be
the default.

(catching up with emails after holiday and I may have missed some of
your arguments)

If we consider ACPI unusable on ARM but we still want to start merging
patches, we should rather make the config option depend on BROKEN
(though if it is that unusable that no real platform can use it, I would
rather not merge it at all at this stage).

I agree here.

I would recommend creating a separate branch for that living outside of the
mainline kernel and merging it when there are real users.

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.