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Subject[PATCH][CFT][2.6.0-test2] local APIC enable fixes
There has been a number of problem reports about local APIC
interacting badly with ACPI on P4s due to the P4 local APIC
force-enable change in 2.5.74,

This patch reverts the 2.5.74 patch, so if the BIOS disables
the local APIC on a P4, we don't enable it by default any more.

The rescue the situation for those P4 systems where the local
APIC _can_ be enabled safely, I've added two kernel parameters
that can be used to override broken BIOSen:
- "nolapic" prevents the kernel from enabling or using the local
APIC. This is stronger than listing a machine in the DMI scan
blacklist, since it also works for machines that boot with the
local APIC already enabled.
- "lapic" tells the kernel to force-enable the P4 local APIC if
the BIOS disabled it. I haven't changed the logic for P6/K7
family processors, so we still force-enable those unless
"nolapic" was passed to the kernel.

The patch also includes a cleanup: the dont_use_local_apic_timer
flag variable is not set any more since 2.5.74, so it's removed.

Please test.

/Mikael

diff -ruN linux-2.6.0-test2/Documentation/kernel-parameters.txt linux-2.6.0-test2.apic-fixes/Documentation/kernel-parameters.txt
--- linux-2.6.0-test2/Documentation/kernel-parameters.txt 2003-07-14 13:17:24.000000000 +0200
+++ linux-2.6.0-test2.apic-fixes/Documentation/kernel-parameters.txt 2003-07-29 15:55:38.000000000 +0200
@@ -436,6 +436,8 @@

l2cr= [PPC]

+ lapic [IA-32,APIC] Enable the local APIC even if BIOS disabled it.
+
lasi= [HW,SCSI] PARISC LASI driver for the 53c700 chip
Format: addr:<io>,irq:<irq>

@@ -625,6 +627,8 @@

nointroute [IA-64]

+ nolapic [IA-32,APIC] Do not enable or use the local APIC.
+
nomce [IA-32] Machine Check Exception

noresume [SWSUSP] Disables resume and restore original swap space.
diff -ruN linux-2.6.0-test2/arch/i386/kernel/apic.c linux-2.6.0-test2.apic-fixes/arch/i386/kernel/apic.c
--- linux-2.6.0-test2/arch/i386/kernel/apic.c 2003-07-03 12:32:41.000000000 +0200
+++ linux-2.6.0-test2.apic-fixes/arch/i386/kernel/apic.c 2003-07-29 15:55:41.000000000 +0200
@@ -594,7 +594,26 @@
* Detect and enable local APICs on non-SMP boards.
* Original code written by Keir Fraser.
*/
-int dont_enable_local_apic __initdata = 0;
+
+/*
+ * Knob to control our willingness to enable the local APIC.
+ */
+int enable_local_apic __initdata = 0; /* -1=force-disable, +1=force-enable */
+
+static int __init lapic_disable(char *str)
+{
+ enable_local_apic = -1;
+ clear_bit(X86_FEATURE_APIC, boot_cpu_data.x86_capability);
+ return 0;
+}
+__setup("nolapic", lapic_disable);
+
+static int __init lapic_enable(char *str)
+{
+ enable_local_apic = 1;
+ return 0;
+}
+__setup("lapic", lapic_enable);

static int __init detect_init_APIC (void)
{
@@ -602,7 +621,7 @@
extern void get_cpu_vendor(struct cpuinfo_x86*);

/* Disabled by DMI scan or kernel option? */
- if (dont_enable_local_apic)
+ if (enable_local_apic < 0)
return -1;

/* Workaround for us being called before identify_cpu(). */
@@ -616,7 +635,7 @@
goto no_apic;
case X86_VENDOR_INTEL:
if (boot_cpu_data.x86 == 6 ||
- boot_cpu_data.x86 == 15 ||
+ (boot_cpu_data.x86 == 15 && (cpu_has_apic || enable_local_apic > 0)) ||
(boot_cpu_data.x86 == 5 && cpu_has_apic))
break;
goto no_apic;
@@ -897,14 +916,8 @@

static unsigned int calibration_result;

-int dont_use_local_apic_timer __initdata = 0;
-
void __init setup_boot_APIC_clock(void)
{
- /* Disabled by DMI scan or kernel option? */
- if (dont_use_local_apic_timer)
- return;
-
printk("Using local APIC timer interrupts.\n");
using_apic_timer = 1;

@@ -1121,6 +1134,9 @@
*/
int __init APIC_init_uniprocessor (void)
{
+ if (enable_local_apic < 0)
+ clear_bit(X86_FEATURE_APIC, boot_cpu_data.x86_capability);
+
if (!smp_found_config && !cpu_has_apic)
return -1;

diff -ruN linux-2.6.0-test2/arch/i386/kernel/dmi_scan.c linux-2.6.0-test2.apic-fixes/arch/i386/kernel/dmi_scan.c
--- linux-2.6.0-test2/arch/i386/kernel/dmi_scan.c 2003-06-17 12:51:19.000000000 +0200
+++ linux-2.6.0-test2.apic-fixes/arch/i386/kernel/dmi_scan.c 2003-07-29 15:55:38.000000000 +0200
@@ -300,9 +300,9 @@
static int __init local_apic_kills_bios(struct dmi_blacklist *d)
{
#ifdef CONFIG_X86_LOCAL_APIC
- extern int dont_enable_local_apic;
- if (!dont_enable_local_apic) {
- dont_enable_local_apic = 1;
+ extern int enable_local_apic;
+ if (enable_local_apic == 0) {
+ enable_local_apic = -1;
printk(KERN_WARNING "%s with broken BIOS detected. "
"Refusing to enable the local APIC.\n",
d->ident);
-
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