ACPI

[Catalin Marinas]

On 26 November 2013 23:32, Matthew Garrett <mjg59 at srcf.ucam.org> wrote:
> On Tue, Nov 26, 2013 at 05:11:23PM -0600, Matt Sealey wrote:
>> But I can't think of a reason why an extension or companion to PSCI
>> couldn't do it, and why you WOULDN'T want to do this as an API
>> implemented via a secure monitor interface which is architecturally
>> defined on ARM where security extensions are present. I can't imagine
>> a reason why it couldn't be done over IPMI to some microcontroller or
>> dedicated external component, for the case of fans and chassis
>> components and tedious other stuff.
>
> Primarily because people want solutions that aren't tied to having an
> entirely separate computer running its own embedded OS. The likely
> alternative to doing things in ACPI would be to do them in TrustZone,
> and let's not encourage that. A significant proportion of the bugs we
> see on x86 are down to SMM code that we can't see, let alone debug. It's
> much easier to handle bugs in code that runs in the same context as the
> OS.

I agree. While I'm pushing for standard firmware interfaces like PSCI
on ARMv8 (Power State Coordination Interface for those who haven't
heard of it yet), I would limit it to things that can only be done
(safely) in secure monitor mode (EL3) like CPU power management (and
that's hotplug/idle, not DVFS).

-- 
Catalin