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Subject[PATCH] Disable APIC on reboot.
Date
Forward port of a patch from Felix [surname mangled by MTA] <fxkuehl@gmx.de>

Original mail:-

when I reboot my laptop the BIOS complains about a keyboard controller
failure and timer interrupts not working. On the BIOS password screen
the keyboard doesn't work. If I disable the BIOS password the system
hangs a bit later on the POST screen. I tried all reboot methods via the
kernel command line without success. I saw this problem with Debian
Woody's precompiled 2.4.18 kernel, self compiled Debian 2.4.20 sources
and Linux 2.4.21-rc1+ACPI patch. This problem only occurs if
CONFIG_X86_LOCAL_APIC is enabled. With CONFIG_X86_LOCAL_APIC disabled it
reboots just fine.

My guess is that it's a BIOS bug as I've never had this problem on other
machines before. I found a workaround: disable the local APIC before
rebooting. I don't really know how it works. Just calling
disable_local_APIC wasn't enough, so I copied a bit more code from
apic_pm_suspend (arch/i386/kernel/apic.c:465) to machine_restart
(arch/i386/kernel/process.c:369). I'm pretty sure that this is not the
proper way to do it but it works here. A patch against 2.4.21-rc1 can be
found at the end of this email.

diff -urpN --exclude-from=/home/davej/.exclude bk-linus/arch/i386/kernel/reboot.c linux-2.5/arch/i386/kernel/reboot.c
--- bk-linus/arch/i386/kernel/reboot.c 2003-05-13 11:51:12.000000000 +0100
+++ linux-2.5/arch/i386/kernel/reboot.c 2003-07-16 02:54:29.000000000 +0100
@@ -8,6 +8,7 @@
#include <linux/interrupt.h>
#include <linux/mc146818rtc.h>
#include <asm/uaccess.h>
+#include <asm/apic.h>
#include "mach_reboot.h"

/*
@@ -250,6 +251,19 @@ void machine_restart(char * __unused)
*/
smp_send_stop();
disable_IO_APIC();
+#else
+#ifdef CONFIG_X86_LOCAL_APIC
+ {
+ unsigned int l, h;
+
+ local_irq_disable();
+ disable_local_APIC();
+ rdmsr(MSR_IA32_APICBASE, l, h);
+ l &= ~MSR_IA32_APICBASE_ENABLE;
+ wrmsr(MSR_IA32_APICBASE, l, h);
+ local_irq_enable();
+}
+#endif
#endif

if(!reboot_thru_bios) {
-
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