linux-kernel - Re: [PATCH V5 18/30] dt-bindings: csky CPU Bindings

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Date:   Fri, 28 Sep 2018 06:32:34 -0500
From:   Rob Herring <robh@...nel.org>
To:     Guo Ren <ren_guo@...ky.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        David Miller <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Mark Rutland <mark.rutland@....com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:GENERIC INCLUDE/ASM HEADER FILES" 
        <linux-arch@...r.kernel.org>, devicetree@...r.kernel.org,
        Greentime Hu <green.hu@...il.com>,
        Palmer Dabbelt <palmer@...ive.com>
Subject: Re: [PATCH V5 18/30] dt-bindings: csky CPU Bindings

On Thu, Sep 27, 2018 at 8:03 PM Guo Ren <ren_guo@...ky.com> wrote:
>
> On Thu, Sep 27, 2018 at 11:43:17AM -0500, Rob Herring wrote:
> > On Tue, Sep 25, 2018 at 07:39:21AM +0800, Guo Ren wrote:
> > > This patch adds the documentation to describe that how to add cpu nodes in
> > > dts for SMP.
> > >
> > > Signed-off-by: Guo Ren <ren_guo@...ky.com>
> > > ---
> > >  Documentation/devicetree/bindings/csky/cpus.txt | 70 +++++++++++++++++++++++++
> > >  1 file changed, 70 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/csky/cpus.txt
> > >
> > > diff --git a/Documentation/devicetree/bindings/csky/cpus.txt b/Documentation/devicetree/bindings/csky/cpus.txt
> > > new file mode 100644
> > > index 0000000..ee3901d
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/csky/cpus.txt
> > > @@ -0,0 +1,70 @@
> > > +==================
> > > +C-SKY CPU Bindings
> > > +==================
> > > +
> > > +The device tree allows to describe the layout of CPUs in a system through
> > > +the "cpus" node, which in turn contains a number of subnodes (ie "cpu")
> > > +defining properties for every cpu.
> > > +
> > > +Only SMP system need to care about the cpus node and single processor
> > > +needn't define cpus node at all.
> >
> > We've generally found this is not true. Even for single core, you can
> > have power domains, clocks for DVFS, etc.
> Ok, I'll remove it.
>
> >
> > > +
> > > +=====================================
> > > +cpus and cpu node bindings definition
> > > +=====================================
> > > +
> > > +- cpus node
> > > +
> > > +        Description: Container of cpu nodes
> > > +
> > > +        The node name must be "cpus".
> > > +
> > > +        A cpus node must define the following properties:
> > > +
> > > +        - #address-cells
> > > +                Usage: required
> > > +                Value type: <u32>
> > > +                Definition: must be set to 1
> > > +        - #size-cells
> > > +                Usage: required
> > > +                Value type: <u32>
> > > +                Definition: must be set to 0
> > > +
> > > +- cpu node
> > > +
> > > +        Description: Describes one of SMP cores
> > > +
> > > +        PROPERTIES
> > > +
> >
> > You need a compatible property for cpu nodes.
> Our cpu is defined in defconfig, not in dts. I could put a comatible
> property in here, but it's no use in code.

It doesn't matter as that could change. Most arches do run-time
selection of cpus within a range of compatible cores.

And read the DT spec (devicetree.org) which says compatible is
required for cpu nodes.

Rob