linux-kernel - Re: [PATCH v6 1/2] of: Documentation: Specify local APIC ID in "reg"

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Date:   Tue, 20 Mar 2018 19:26:12 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ivan Gorinov <ivan.gorinov@...el.com>
cc:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v6 1/2] of: Documentation: Specify local APIC ID in
 "reg"

On Tue, 20 Mar 2018, Ivan Gorinov wrote:

> On Mon, Mar 19, 2018 at 07:39:52PM -0500, Rob Herring wrote:
> > On Tue, Mar 13, 2018 at 5:05 PM, Ivan Gorinov <ivan.gorinov@...el.com> wrote:
> > > Use the "reg" property to specify the processor's local APIC ID.
> > > Local APIC ID is assigned by hardware and may differ from CPU number.
> > 
> > Is "CPU number" a s/w visible h/w number or has it just been an index
> > for DT? In the latter case, I'm okay with this change. In the former
> > case, you should stick to the existing numbering. For example on ARM,
> > the number here corresponds to a core ID number in a register called
> > MPIDR.
> 
> The latter case. Apparently, "CPU number" was just an index in the list.
> Local APIC ID is the s/w visible h/w assigned number.
> Some processor models allow local APIC ID to be changed by software, but
> CPUID instruction executed with %eax = 0x0b always returns the initial ID
> assigned by hardware in %edx.
> 
> APIC ID does not match index in the list in many systems.

Please document that in the changelog.

Thanks,

	tglx