Re: [PATCH RFC 16/35] ARM64 / ACPI: Parse GTDT to initialize timer

[Ian Campbell <Ian.Campbell@citrix.com>]

On Wed, 2015-02-04 at 21:51 +0000, Julien Grall wrote:
> > +    res = platform_init_time();
> 
> The platform code is DT-centrict.

This is an interesting point. Given the stated goals and reasons for
having ACPI on ARM it seems to me that in general nothing under
xen/arch/arm/platforms/* should ever be needed, and certainly not things
like platform time init which we should insist have been setup correctly
by the platform.

It's possible that we might need some concept of ACPI quirks at some
point, but lets have a simple rule for now:

      * The initial set of core ACPI patches for Xen should not ever
        call into any platform specific code.

If there turns out to be a need to call platform code in this initial
series then it must be in a separate patch towards the end of the
series, after all the core code has been introduced. The patch
description should contain a detailed justification as to why this
platform specific code is required.

I think it is probable that any ACPI quirks should be separate from the
(DT-based) xen/arch/arm/platforms/* stuff, but lets see what, if
anything, turns out to be needed.

Perhaps platform_* should all grow an "ASSERT(!in acpi mode)" (or
"ASSERT(in dt mode)") to help enforce this.

Ian.