linux-kernel - Re: [PATCH v2 1/5] x86/topology: Export helper to get CPU number from APIC ID

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Date: Mon, 1 Jul 2024 13:51:42 -0400
From: Yazen Ghannam <yazen.ghannam@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: Thomas Gleixner <tglx@...utronix.de>, linux-edac@...r.kernel.org,
	linux-kernel@...r.kernel.org, tony.luck@...el.com, x86@...nel.org,
	avadhut.naik@....com, john.allen@....com
Subject: Re: [PATCH v2 1/5] x86/topology: Export helper to get CPU number
 from APIC ID

On Fri, Jun 28, 2024 at 04:45:35PM +0200, Borislav Petkov wrote:
> On Fri, Jun 28, 2024 at 10:15:42AM -0400, Yazen Ghannam wrote:
> > Thanks for the tip. It looks to me that SMP and X86_LOCAL_APIC are
> > generally independent.
> 
> They are?
> 
> config X86_LOCAL_APIC
>         def_bool y
>         depends on X86_64 || SMP
> 	^^^^^^^		     ^^^
>

Right, SMP does not depend on X86_LOCAL_APIC. Otherwise, there would be
a circular dependency here.

X86_LOCAL_APIC depends on the logical OR of a bunch of options. So it
depends on "any one" of the options to be enabled. But it doesn't need
all of them.

config UP_LATE_INIT
        def_bool y
        depends on !SMP && X86_LOCAL_APIC
	           ^^^^^^^^^^^^

This shows that X86_LOCAL_APIC doesn't have a hard dependency on SMP.
Otherwise, this option would never work.

Thanks,
Yazen