linux-kernel - Re: [RFC PATCH v2 10/10] dt-bindings: Document devicetree binding for ARM SPE

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Date:   Mon, 16 Jan 2017 10:59:04 +0000
From:   Will Deacon <will.deacon@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, marc.zyngier@....com,
        kim.phillips@....com, alex.bennee@...aro.org,
        christoffer.dall@...aro.org, tglx@...utronix.de,
        peterz@...radead.org, alexander.shishkin@...ux.intel.com,
        robh@...nel.org, suzuki.poulose@....com, pawel.moll@....com,
        mathieu.poirier@...aro.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 10/10] dt-bindings: Document devicetree binding
 for ARM SPE

On Fri, Jan 13, 2017 at 06:43:52PM +0000, Mark Rutland wrote:
> On Fri, Jan 13, 2017 at 04:03:49PM +0000, Will Deacon wrote:
> > This patch documents the devicetree binding in use for ARM SPE.
> > 
> > Cc: Mark Rutland <mark.rutland@....com>
> > Cc: Rob Herring <robh@...nel.org>
> > Signed-off-by: Will Deacon <will.deacon@....com>
> > ---
> >  Documentation/devicetree/bindings/arm/spe-pmu.txt | 20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/arm/spe-pmu.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/arm/spe-pmu.txt b/Documentation/devicetree/bindings/arm/spe-pmu.txt
> > new file mode 100644
> > index 000000000000..d6540b491af4
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/arm/spe-pmu.txt
> > @@ -0,0 +1,20 @@
> > +* ARMv8.2 Statistical Profiling Extension (SPE) Performance Monitor Units (PMU)
> > +
> > +ARMv8.2 introduces the optional Statistical Profiling Extension for collecting
> > +performance sample data using an in-memory trace buffer.
> > +
> > +** SPE Required properties:
> > +
> > +- compatible : should be one of:
> > +	       "arm,arm-spe-pmu-v1"
> 
> The second "arm" here doesn't seem to add much. Should that be "armv8.2"
> instead?

I don't think armv8.2 is particularly helpful, because that effectively ties
together the SPE version and the architecture version, which I don't think
is strictly required. The reason I added it was so that you could describe
a partner implementation as something like:

  acme,arm-spe-pmu-v1

and know that it was acme's implementation of an ARM architectural feature.

If I drop the second "arm", I was worried that it might conflict with other
namespaces (e.g. acme's signal-processing-element's power-management-unit).

What do you reckon?

Will