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x86, ioapic: Avoid writing io_apic id if already correct

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For 32bit mptable path, setup_ids_from_mpc() always writes the io_apic
id register, even there is no change needed.

Skip the write, when readout and mptable match.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
LKML-Reference: <4CFDF785.7010401@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Yinghai Lu 2010-12-07 00:59:49 -08:00 committed by Thomas Gleixner
parent 0450193bff
commit 60d79fd99f
1 changed files with 5 additions and 2 deletions
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7
arch/x86/kernel/apic/io_apic.c
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@ -2007,9 +2007,12 @@ void __init setup_ioapic_ids_from_mpc_nocheck(void)
= mp_ioapics[apic_id].apicid;
/*
* Read the right value from the MPC table and
* write it into the ID register.
* Update the ID register according to the right value
* from the MPC table if they are different.
*/
if (mp_ioapics[apic_id].apicid == reg_00.bits.ID)
continue;
apic_printk(APIC_VERBOSE, KERN_INFO
"...changing IO-APIC physical APIC ID to %d ...",
mp_ioapics[apic_id].apicid);