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[PATCH 4/8] x86: I/O APIC: Keep IRQ off when changing LVT registers

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From: Maciej W. Rozycki <macro@...>
To: Ingo Molnar <mingo@...>
Cc: Thomas Gleixner <tglx@...>, H. Peter Anvin <hpa@...>, <linux-kernel@...>
Subject: [PATCH 4/8] x86: I/O APIC: Keep IRQ off when changing LVT registers
Date: Wednesday, May 21, 2008 - 5:09 pm

Disable the 8259A acting in the "virtual wire" mode to keep the interrupt
line inactive while fiddling with local APIC interrupt vector registers
associated with its destination inputs.  To be on the safe side, 
especially concerning flipping the trigger mode.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
---
patch-2.6.26-rc1-20080505-timer-8259-nmi-unmask-0
diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/arch/x86/kernel/io_apic_32.c linux-2.6.26-rc1-20080505/arch/x86/kernel/io_apic_32.c
--- linux-2.6.26-rc1-20080505.macro/arch/x86/kernel/io_apic_32.c	2008-05-21 18:52:36.000000000 +0000
+++ linux-2.6.26-rc1-20080505/arch/x86/kernel/io_apic_32.c	2008-05-21 18:52:36.000000000 +0000
@@ -2199,7 +2199,9 @@ static inline void __init check_timer(vo
 			else
 				add_pin_to_irq(0, apic2, pin2);
 			if (nmi_watchdog == NMI_IO_APIC) {
+				disable_8259A_irq(0);
 				setup_nmi();
+				enable_8259A_irq(0);
 			}
 			goto out;
 		}
diff -up --recursive --new-file linux-2.6.26-rc1-20080505.macro/arch/x86/kernel/io_apic_64.c linux-2.6.26-rc1-20080505/arch/x86/kernel/io_apic_64.c
--- linux-2.6.26-rc1-20080505.macro/arch/x86/kernel/io_apic_64.c	2008-05-21 19:00:05.000000000 +0000
+++ linux-2.6.26-rc1-20080505/arch/x86/kernel/io_apic_64.c	2008-05-18 00:24:43.000000000 +0000
@@ -1702,7 +1702,9 @@ static inline void __init check_timer(vo
 			apic_printk(APIC_VERBOSE," works.\n");
 			nmi_watchdog_default();
 			if (nmi_watchdog == NMI_IO_APIC) {
+				disable_8259A_irq(0);
 				setup_nmi();
+				enable_8259A_irq(0);
 			}
 			goto out;
 		}
--
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[PATCH 4/8] x86: I/O APIC: Keep IRQ off when changing LVT re..., Maciej W. Rozycki, (Wed May 21, 5:09 pm)