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Subject[PATCH 2/4] [APIC] Allow disabling of UP APIC/IO-APIC by default, with command line option to turn it on.
Date
Signed-off-by: Ben Collins <bcollins@ubuntu.com>
---
arch/i386/Kconfig | 13 +++++++++++++
arch/i386/kernel/apic.c | 13 +++++++++++--
arch/i386/kernel/io_apic.c | 10 +++++++++-
include/asm-i386/apic.h | 6 ++++++
include/asm-i386/io_apic.h | 5 +++++
5 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig
index b4a2461..ef2f2db 100644
--- a/arch/i386/Kconfig
+++ b/arch/i386/Kconfig
@@ -285,6 +285,19 @@ config X86_UP_IOAPIC
to use it. If you say Y here even though your machine doesn't have
an IO-APIC, then the kernel will still run with no slowdown at all.

+config X86_UP_APIC_DEFAULT_OFF
+ bool "APIC support on uniprocessors defaults to off"
+ depends on X86_UP_APIC
+ default n
+ help
+ Some older systems have flaky APICs. Say Y to turn off APIC
+ support by default, while still allowing it to be enabled by the
+ "lapic" and "apic" command line options.
+
+ Usually this is only necessary for distro installer kernels that
+ must work with everything. Everyone else can safely say N here
+ and configure APIC support in or out as needed.
+
config X86_LOCAL_APIC
bool
depends on X86_UP_APIC || ((X86_VISWS || SMP) && !X86_VOYAGER) || X86_GENERICARCH
diff --git a/arch/i386/kernel/apic.c b/arch/i386/kernel/apic.c
index 2fd4b7d..2f2eb83 100644
--- a/arch/i386/kernel/apic.c
+++ b/arch/i386/kernel/apic.c
@@ -51,8 +51,9 @@ static cpumask_t timer_bcast_ipi;

/*
* Knob to control our willingness to enable the local APIC.
+ * -2=default-disable, -1=force-disable, 1=force-enable, 0=automatic
*/
-static int enable_local_apic __initdata = 0; /* -1=force-disable, +1=force-enable */
+static int enable_local_apic __initdata = (X86_APIC_DEFAULT_OFF ? -2 : 0);

static inline void lapic_disable(void)
{
@@ -801,7 +802,7 @@ static int __init detect_init_APIC (void
* APIC only if "lapic" specified.
*/
if (enable_local_apic <= 0) {
- printk("Local APIC disabled by BIOS -- "
+ printk("Local APIC disabled by BIOS (or by default) -- "
"you can enable it with \"lapic\"\n");
return -1;
}
@@ -1350,6 +1351,14 @@ int __init APIC_init_uniprocessor (void)
if (!smp_found_config && !cpu_has_apic)
return -1;

+ /* If local apic is off due to config_x86_apic_off option, jump
+ * out here. */
+ if (enable_local_apic < -1) {
+ printk(KERN_INFO "Local APIC disabled by default -- "
+ "use 'lapic' to enable it.\n");
+ return -1;
+ }
+
/*
* Complain if the BIOS pretends there is one.
*/
diff --git a/arch/i386/kernel/io_apic.c b/arch/i386/kernel/io_apic.c
index 3b7a63e..0122dba 100644
--- a/arch/i386/kernel/io_apic.c
+++ b/arch/i386/kernel/io_apic.c
@@ -767,7 +767,7 @@ #endif /* !CONFIG_SMP */
#define MAX_PIRQS 8
static int pirq_entries [MAX_PIRQS];
static int pirqs_enabled;
-int skip_ioapic_setup;
+int skip_ioapic_setup = X86_APIC_DEFAULT_OFF;

static int __init ioapic_setup(char *str)
{
@@ -2887,3 +2887,11 @@ static int __init parse_noapic(char *arg
return 0;
}
early_param("noapic", parse_noapic);
+
+static int __init parse_apic(char *arg)
+{
+ /* enable IO-APIC */
+ enable_ioapic_setup();
+ return 0;
+}
+early_param("apic", parse_apic);
diff --git a/include/asm-i386/apic.h b/include/asm-i386/apic.h
index b952957..a06ca3f 100644
--- a/include/asm-i386/apic.h
+++ b/include/asm-i386/apic.h
@@ -71,6 +71,12 @@ # define apic_read_around(x) apic_read(x
# define apic_write_around(x,y) apic_write_atomic((x),(y))
#endif

+#ifdef CONFIG_X86_UP_APIC_DEFAULT_OFF
+# define X86_APIC_DEFAULT_OFF 1
+#else
+# define X86_APIC_DEFAULT_OFF 0
+#endif
+
static inline void ack_APIC_irq(void)
{
/*
diff --git a/include/asm-i386/io_apic.h b/include/asm-i386/io_apic.h
index 059a9ff..ddedeec 100644
--- a/include/asm-i386/io_apic.h
+++ b/include/asm-i386/io_apic.h
@@ -126,6 +126,11 @@ static inline void disable_ioapic_setup(
skip_ioapic_setup = 1;
}

+static inline void enable_ioapic_setup(void)
+{
+ skip_ioapic_setup = 0;
+}
+
static inline int ioapic_setup_disabled(void)
{
return skip_ioapic_setup;
--
1.4.1
-
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