linux-kernel - Re: [PATCH v3 6/7] arm64: topology: Enable ACPI/PPTT based CPU topology.

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Date:   Fri, 20 Oct 2017 10:22:10 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     linux-acpi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        sudeep.holla@....com, hanjun.guo@...aro.org, rjw@...ysocki.net,
        will.deacon@....com, catalin.marinas@....com,
        gregkh@...uxfoundation.org, viresh.kumar@...aro.org,
        mark.rutland@....com, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, jhugo@...eaurora.org,
        wangxiongfeng2@...wei.com, Jonathan.Zhang@...ium.com,
        ahs3@...hat.com, Jayachandran.Nair@...ium.com,
        austinwc@...eaurora.org
Subject: Re: [PATCH v3 6/7] arm64: topology: Enable ACPI/PPTT based CPU
 topology.

On Thu, Oct 19, 2017 at 11:54:22AM -0500, Jeremy Linton wrote:

[...]

> >>+			cpu_topology[cpu].core_id   = topology_id;
> >>+			topology_id = setup_acpi_cpu_topology(cpu, 2);
> >>+			cpu_topology[cpu].cluster_id = topology_id;
> >>+			topology_id = setup_acpi_cpu_topology(cpu, max_topo);
> >
> >If you want a package id (that's just a package tag to group cores), you
> >should not use a large level because you know how setup_acpi_cpu_topology()works, you should add an API that allows you to retrieve the package id
> >(so that you can use th ACPI_PPTT_PHYSICAL_PACKAGE flag consistenly,
> >whatever it represents).
> 
> I don't think the spec requires the use of PHYSICAL_PACKAGE... Am I
> misreading it? Which means we need to "pick" a node level to
> represent the physical package if one doesn't exist...

The specs define a means to detect if a given PPTT node corresponds to a
package (I am refraining from stating again that to me that's not clean
cut what a package is _architecturally_, I think you know my POV by now)
and that's what you need to use to retrieve a packageid for a given cpu,
if I understand the aim of the physical package flag.

Either that or that flag is completely useless.

Lorenzo

ACPI 6.2 - Table 5-151 (page 248)
Physical package
-----------------
Set to 1 if this node of the processor topology represents the boundary
of a physical package, whether socketed or surface mounted.  Set to 0 if
this instance of the processor topology does not represent the boundary
of a physical package.