[PATCH v1 2/2] Documentation: devicetree: Add new binding for PSCIv0.2

[Mark Rutland]

On Thu, Mar 20, 2014 at 03:03:19AM +0000, Christoffer Dall wrote:
> On Wed, Mar 19, 2014 at 08:54:25PM -0400, Ashwin Chaugule wrote:
> > The PSCI v0.2+ spec defines static values for PSCI function IDs.
> > Add a new binding entry so that pre v0.2 implementations can
> > use DT entries for function IDs and v0.2+ implementations use
> > static entries as defined by the PSCIv0.2 specification.
> > 
> > Signed-off-by: Ashwin Chaugule <ashwin.chaugule at linaro.org>
> > ---
> >  Documentation/devicetree/bindings/arm/psci.txt | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/arm/psci.txt b/Documentation/devicetree/bindings/arm/psci.txt
> > index 433afe9..a808284 100644
> > --- a/Documentation/devicetree/bindings/arm/psci.txt
> > +++ b/Documentation/devicetree/bindings/arm/psci.txt
> > @@ -21,7 +21,11 @@ to #0.
> >  
> >  Main node required properties:
> >  
> > - - compatible    : Must be "arm,psci"
> > + - compatible    : "arm,psci" : pre PSCIv0.2 spec implementations use this
> > +                   to get the function IDs from DT entries.
> > +
> > +                   "arm,psci-0.2": PSCIv0.2+ spec implementations use static
> > +                   values for function IDs as defined in the spec.

How about:

- compatible: should contain at least one of:

  * "arm,psci" : for implementations complying to PSCI versions prior to
    0.2. For these cases function IDs must be provided.

  * "arm,psci-0.2" : for implementations complying to PSCI 0.2. Function
    IDs are not required and should be ignored by an OS with PSCI 0.2
    support, but are permitted to be present for compatibility with
    existing software when "arm,psci" is later in the compatible list.

> Maybe specify that in this case no function IDs are passed in the device
> tree?

As described above, for compatibility with existing kernels, the
hypervisor will likely want to provide IDs, e.g.

psci {
	compatible = "arm,psci-0.2", "arm,psci";
	method = "hvc";

	cpu_on = < arbitrary value >;
	cpu_off = < arbitrary value >;

	...
};

In this case I'd expect an OS with PSCI 0.2 support to use the PSCI 0.2
IDs, but an older OS would use the IDs from the DT (which may or may not
match the PSCI 0.2 IDs).

So while we should say is any function IDs should be ignored for
"arm,psci-0.2", we shouldn't say that they are disallowed in the node.

The document should have examples of "arm,psci" only, "arm,psci-0.2"
only, and the compatibility case.

Cheers,
Mark.