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Diffstat (limited to 'arch/x86/kernel/io_apic_64.c')
-rw-r--r--arch/x86/kernel/io_apic_64.c25
1 files changed, 16 insertions, 9 deletions
diff --git a/arch/x86/kernel/io_apic_64.c b/arch/x86/kernel/io_apic_64.c
index 07ebcd305fb..9e645cba11c 100644
--- a/arch/x86/kernel/io_apic_64.c
+++ b/arch/x86/kernel/io_apic_64.c
@@ -1823,11 +1823,21 @@ static int __init notimercheck(char *s)
__setup("no_timer_check", notimercheck);
/*
- *
- * IRQs that are handled by the PIC in the MPS IOAPIC case.
- * - IRQ2 is the cascade IRQ, and cannot be a io-apic IRQ.
- * Linux doesn't really care, as it's not actually used
- * for any interrupt handling anyway.
+ * Traditionally ISA IRQ2 is the cascade IRQ, and is not available
+ * to devices. However there may be an I/O APIC pin available for
+ * this interrupt regardless. The pin may be left unconnected, but
+ * typically it will be reused as an ExtINT cascade interrupt for
+ * the master 8259A. In the MPS case such a pin will normally be
+ * reported as an ExtINT interrupt in the MP table. With ACPI
+ * there is no provision for ExtINT interrupts, and in the absence
+ * of an override it would be treated as an ordinary ISA I/O APIC
+ * interrupt, that is edge-triggered and unmasked by default. We
+ * used to do this, but it caused problems on some systems because
+ * of the NMI watchdog and sometimes IRQ0 of the 8254 timer using
+ * the same ExtINT cascade interrupt to drive the local APIC of the
+ * bootstrap processor. Therefore we refrain from routing IRQ2 to
+ * the I/O APIC in all cases now. No actual device should request
+ * it anyway. --macro
*/
#define PIC_IRQS (1<<2)
@@ -1838,10 +1848,7 @@ void __init setup_IO_APIC(void)
* calling enable_IO_APIC() is moved to setup_local_APIC for BP
*/
- if (acpi_ioapic)
- io_apic_irqs = ~0; /* all IRQs go through IOAPIC */
- else
- io_apic_irqs = ~PIC_IRQS;
+ io_apic_irqs = ~PIC_IRQS;
apic_printk(APIC_VERBOSE, "ENABLING IO-APIC IRQs\n");