From: Yinghai Lu <yinghai@kernel.org>
Date: Tue, 7 Dec 2010 08:59:49 +0000 (-0800)
Subject: x86, ioapic: Avoid writing io_apic id if already correct
X-Git-Tag: Ubuntu-5.4-5.4.0-11.14~23660^2~4
X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=60d79fd99ff3b9c692b260a4d53a203f537c052a;p=mirror_ubuntu-focal-kernel.git

x86, ioapic: Avoid writing io_apic id if already correct

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>
---

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 4abf08aab3d4..8a0215042a5f 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -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);