linux-kernel - Re: [RFC 1/2] dt-bindings: topology: Add RISC-V cpu topology.

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Date:   Fri, 2 Nov 2018 15:50:38 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Atish Patra <atish.patra@....com>, linux-riscv@...ts.infradead.org,
        Palmer Dabbelt <palmer@...ive.com>,
        Anup Patel <anup@...infault.org>,
        Christoph Hellwig <hch@...radead.org>, Damien.LeMoal@....com,
        Thomas Gleixner <tglx@...utronix.de>,
        Mark Rutland <mark.rutland@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org, alankao@...estech.com,
        Sudeep Holla <sudeep.holla@....com>,
        Zong Li <zong@...estech.com>
Subject: Re: [RFC 1/2] dt-bindings: topology: Add RISC-V cpu topology.

On Fri, Nov 02, 2018 at 10:11:38AM -0500, Rob Herring wrote:
> On Fri, Nov 2, 2018 at 8:31 AM Sudeep Holla <sudeep.holla@....com> wrote:
> >
> > On Fri, Nov 02, 2018 at 08:09:39AM -0500, Rob Herring wrote:
> > > On Thu, Nov 1, 2018 at 6:04 PM Atish Patra <atish.patra@....com> wrote:
> > > >
> > > > Define a RISC-V cpu topology. This is based on cpu-map in ARM world.
> > > > But it doesn't need a separate thread node for defining SMT systems.
> > > > Multiple cpu phandle properties can be parsed to identify the sibling
> > > > hardware threads. Moreover, we do not have cluster concept in RISC-V.
> > > > So package is a better word choice than cluster for RISC-V.
> > >
> > > There was a proposal to add package info for ARM recently. Not sure
> > > what happened to that, but we don't need 2 different ways.
> > >
> >
> > We still need that, I can brush it up and post what Lorenzo had previously
> > proposed[1]. We want to keep both DT and ACPI CPU topology story aligned.
>
> Frankly, I don't care what the ACPI story is. I care whether each cpu

Sorry I meant feature parity with ACPI and didn't refer to the mechanics.

> arch does its own thing in DT or not. If a package prop works for
> RISC-V folks and that happens to align with ACPI, then okay. Though I
> tend to prefer a package represented as a node rather than a property
> as I think that's more consistent.
>

Sounds good. One of the reason for making it *optional* property is for
backward compatibility. But we should be able to deal with that even with
node.

> Any comments on the thread aspect (whether it has ever been used)?
> Though I think thread as a node level is more consistent with each
> topology level being a node (same with package).
>
Not 100% sure, the only multi threaded core in the market I know is
Cavium TX2 which is ACPI.

--
Regards,
Sudeep