Merge tag 'v3.16-rc1' into x86/cpufeature

Linux 3.16-rc1

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 19 insertions, 1 deletions

diff --git a/arch/x86/kernel/i8259.c b/arch/x86/kernel/i8259.c
index 2e977b5d61dd..8af817105e29 100644
--- a/arch/x86/kernel/i8259.c
+++ b/arch/x86/kernel/i8259.c
@@ -299,13 +299,31 @@ static void unmask_8259A(void)
 static void init_8259A(int auto_eoi)
 {
 	unsigned long flags;
+	unsigned char probe_val = ~(1 << PIC_CASCADE_IR);
+	unsigned char new_val;
 
 	i8259A_auto_eoi = auto_eoi;
 
 	raw_spin_lock_irqsave(&i8259A_lock, flags);
 
-	outb(0xff, PIC_MASTER_IMR);	/* mask all of 8259A-1 */
+	/*
+	 * Check to see if we have a PIC.
+	 * Mask all except the cascade and read
+	 * back the value we just wrote. If we don't
+	 * have a PIC, we will read 0xff as opposed to the
+	 * value we wrote.
+	 */
 	outb(0xff, PIC_SLAVE_IMR);	/* mask all of 8259A-2 */
+	outb(probe_val, PIC_MASTER_IMR);
+	new_val = inb(PIC_MASTER_IMR);
+	if (new_val != probe_val) {
+		printk(KERN_INFO "Using NULL legacy PIC\n");
+		legacy_pic = &null_legacy_pic;
+		raw_spin_unlock_irqrestore(&i8259A_lock, flags);
+		return;
+	}
+
+	outb(0xff, PIC_MASTER_IMR);	/* mask all of 8259A-1 */
 
 	/*
 	 * outb_pic - this has to work on a wide range of PC hardware.