Re: [PATCH v4] dt: update PSCI binding documentation for v0.2

[Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>]

On Fri, Sep 20, 2013 at 05:36:51AM +0100, Olof Johansson wrote:
> Hi,

Hi Olof,

> 
> Just a quick drive-by. Sorry, I don't know the history of previous
> review cycles.
> 
> 
> On Thu, Sep 19, 2013 at 2:24 PM, Rob Herring <robherring2-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> 
> >  Main node optional properties:
> >
> > - - cpu_suspend   : Function ID for CPU_SUSPEND operation
> > + - cpu_suspend[-<32|64]   : Function ID for CPU_SUSPEND operation
> > +
> > + - cpu_off                : Function ID for CPU_OFF operation
> > +
> > + - cpu_on[-<32|64]        : Function ID for CPU_ON operation
> > +
> > + - affinity_info[-<32|64] : Function ID for AFFINITY_INFO operation
> >
> > - - cpu_off       : Function ID for CPU_OFF operation
> > + - migrate[-<32|64]       : Function ID for MIGRATE operation
> >
> > - - cpu_on        : Function ID for CPU_ON operation
> > + - migrate_info_type      : Function ID for MIGRATE_INFO_TYPE operation
> >
> > - - migrate       : Function ID for MIGRATE operation
> > + - migrate_info_up_cpu[-<32|64] : Function ID for MIGRATE_INFO_UP_CPU operation
> >
> > + - system_reset           : Function ID for SYSTEM_RESET operation
> > +
> > + - system_off             : Function ID for SYSTEM_OFF operation
> 
> All of these should use dashes instead of underscores.

I also don't like the underscores, but they're an unfortunate historical
artifact that we can't get rid of (at least for cpu_on, cpu_off, and
cpu_suspend).

Both Xen and kvmtool are already passing DTs to guests which have
underscores in the property names, so it's both a boot ABI and a
userspace ABI.

One aim with this update is to ensure that the new binding maintains a
level of forward compatibility for OSs -- the PSCI 0.2 binding needs to
be a superset of the existing PSCI binding to allow Xen and KVM to
provide PSCI 0.2 functionality without sacrificing the ability to boot
older guests (kvmtool could be given a flag to choose what version of
PSCI to provide, but I'm not sure that can be done for Xen).

Given that, I'm not sure if it makes sense to force the rest to have
dashes rather than underscores -- it'll leave the binding more
inconsistent.

> 
> I also wonder if it would be better to move them into a subnode to
> keep the namespace a bit cleaner.

For the compatibility reasons above, I don't think we can do this. At
least the existing IDs (cpu_on, cpu_off, and cpu_suspend) would need to
be described in the psci node rather than a child.

> 
> > +Some functions have have separate IDs for 32-bit and 64-bit calling
> > +conventions. These separate function IDs are described with function names with
> > +"-64" and "-32" suffixes (e.g. cpu_on-64). Where a function name does not have
> > +a suffix, the ID may be used with either calling convention depending on the
> > +CPU state -- AArch32 callers should use the 32-bit calling convention, and
> > +AArch64 callers should use the 64-bit calling convention.
> 
> Why not just make them a possible two-element property with <32 64>,
> or if only one element, same on both? Seems cleaner.

A 64-bit platform may not have 32-bit call support, and we wouldn't be
able to describe that with a <32 64> property format. As it is valid for
a 64-bit OS to make 32-bit calls, we need to not describe a 32-bit call
ID in that case.

Cheers,
Mark.
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