2 files changed, 19 insertions, 10 deletions

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 76f98fe5b35c..a450373e8e91 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -132,15 +132,6 @@ static void __init ms_hyperv_init_platform(void)
                 lapic_timer_frequency = hv_lapic_frequency;
                 printk(KERN_INFO "HyperV: LAPIC Timer Frequency: %#x\n",
                                 lapic_timer_frequency);
-
-                /*
-                 * On Hyper-V, when we are booting off an EFI firmware stack,
-                 * we do not have many legacy devices including PIC, PIT etc.
-                 */
-                if (efi_enabled(EFI_BOOT)) {
-                        printk(KERN_INFO "HyperV: Using null_legacy_pic\n");
-                        legacy_pic = &null_legacy_pic;
-                }
         }
 #endif
 
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.