linux-kernel - Re: Is this code chunk in init_apic

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Date:   Sat, 07 Mar 2020 12:27:50 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Cao jin <caoj.fnst@...fujitsu.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
Subject: Re: Is this code chunk in init_apic_mappings() superfluous?

Cao jin <caoj.fnst@...fujitsu.com> writes:
> Hi,
>
> I am trying to figure the following code chunk out:
>
> 	if (x2apic_mode) {
> 		boot_cpu_physical_apicid = read_apic_id();
> 		return;
> 	}
>
> As my understanding, even in x2APIC mode, boot_cpu_physical_apicid is
> also got via early_acpi_process_madt --> ... --> register_lapic_address,
> so, is it for any corner case I am not aware?

The case when there are neither ACPI nor valid mptables. Unlikely, but
possible in theory.

Thanks,

        tglx