ACPI

[Nicolas Pitre]

On Wed, 27 Nov 2013, Catalin Marinas wrote:

> 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).

And as we both know, even hotplug/idle may get quite complicated and bug 
prone in some circumstances.


Nicolas