Re: [RFC PATCH v3 02/17] Documentation: devicetree: arm: cpus/cpu nodes bindings updates

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

On Fri, Apr 26, 2013 at 11:18:40AM +0100, Lorenzo Pieralisi wrote:
> On Fri, Apr 26, 2013 at 03:51:10AM +0100, Rob Herring wrote:
> > On Wed, Apr 24, 2013 at 12:28 PM, Lorenzo Pieralisi
> > <lorenzo.pieralisi-5wv7dgnIgG8@public.gmane.org> wrote:
> > > In order to extend the current cpu nodes bindings to newer CPUs
> > > inclusive of AArch64 and to update support for older ARM CPUs this
> > > patch updates device tree documentation for the cpu nodes bindings.
> > >
> > > Main changes:
> > >     - adds 64-bit bindings
> > >     - define usage of #address-cells
> > >     - define 32/64 dts compatibility settings
> > >     - defines behaviour on pre and post v7 uniprocessor systems
> > >     - adds ARM 11MPcore specific reg property definition
> > >
> > > Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi-5wv7dgnIgG8@public.gmane.org>
> > > ---
> > 
> > [...]
> > 
> > > +       - enable-method
> > > +               Value type: <stringlist>
> > > +               Usage and definition depend on ARM architecture version and
> > > +               configuration:
> > > +                       # On ARM v8 64-bit systems running the OS in AArch64,
> > > +                         this property is required and must be "spin-table".
> > 
> > What about PSCI?
> 
> I should add it, at least for ARM v8.

It's worth noting KVM uses it on v7 too, so it should be available for CPUs
that are v7+.

> 
> > I don't think the ePAPR spin-table definition is sufficient for ARM.
> > How do you define wake up by SGI or sev instruction.
> 
> I think Will described the wfe/sev mechanism in:
> 
> Documentation/arm64/booting.txt
> 
> and the ePAPR does the same in 5.5.2.2/5.5.2.3. Since this is a document
> describing cpus/cpu nodes bindings I assume that description does not
> belong here. Question is: do we need to specify an ARM implementation
> specific enable-method to describe SGI/sev wake-up (ePAPR 5.5.3) ?
> 
> > > +                       # On ARM 32-bit systems or ARM v8 systems running
> > > +                         the OS in AArch32 this property is prohibited.
> > 
> > Why?
> 
> Because if we define it optional with no possible set of values basically
> it can be whatever string. I could define it optional with the same
> allowed values as ARM v8 even if it is currently ignored, at least in Linux,
> until PSCI implementations get merged.

I believe kvmtool sets the enable-method to "psci" on v7, though I may be
mistaken. Adding Marc to Cc as he knows better.

Cheers,
Mark.