i8259: add -no-spurious-interrupt-hack option

This patch provides a way to optionally suppress spurious interrupts,
as a workaround for systems described below:

Some old operating systems do not handle spurious interrupts well,
and qemu tends to generate them significantly more often than
real hardware.

Examples:
  - Microport UNIX System V/386 v 2.1 (ca 1987)
    (The main problem I'm fixing: Without this patch, it panics
    sporadically when accessing the hard disk.)
  - AT&T UNIX System V/386 Release 4.0 Version 2.1a (ca 1991)
    See screenshot in "QEMU Official OS Support List":
    http://www.claunia.com/qemu/objectManager.php?sClass=application&iId=9
    (I don't have this system to test.)
  - A report about OS/2 boot lockup from 2004 by Hampa Hug:
    http://lists.nongnu.org/archive/html/qemu-devel/2004-09/msg00367.html
    (My patch was partially inspired by his.)
    Also: http://lists.nongnu.org/archive/html/qemu-devel/2005-06/msg00243.html
    (I don't have this system to test.)

Signed-off-by: Matthew Ogilvie <mmogilvi_qemu@miniinfo.net>
Signed-off-by: malc <av1474@comtv.ru>

1 files changed, 18 insertions, 0 deletions

diff --git a/hw/i8259.c b/hw/i8259.c
index 65876662a1..7ecb7e1de6 100644
--- a/hw/i8259.c
+++ b/hw/i8259.c
@@ -26,6 +26,7 @@
 #include "isa.h"
 #include "monitor.h"
 #include "qemu-timer.h"
+#include "sysemu.h"
 #include "i8259_internal.h"
 
 /* debug PIC */
@@ -193,6 +194,20 @@ int pic_read_irq(DeviceState *d)
                 pic_intack(slave_pic, irq2);
             } else {
                 /* spurious IRQ on slave controller */
+                if (no_spurious_interrupt_hack) {
+                    /* Pretend it was delivered and acknowledged.  If
+                     * it was spurious due to slave_pic->imr, then
+                     * as soon as the mask is cleared, the slave will
+                     * re-trigger IRQ2 on the master.  If it is spurious for
+                     * some other reason, make sure we don't keep trying
+                     * to half-process the same spurious interrupt over
+                     * and over again.
+                     */
+                    s->irr &= ~(1<<irq);
+                    s->last_irr &= ~(1<<irq);
+                    s->isr &= ~(1<<irq);
+                    return -1;
+                }
                 irq2 = 7;
             }
             intno = slave_pic->irq_base + irq2;
@@ -202,6 +217,9 @@ int pic_read_irq(DeviceState *d)
         pic_intack(s, irq);
     } else {
         /* spurious IRQ on host controller */
+        if (no_spurious_interrupt_hack) {
+            return -1;
+        }
         irq = 7;
         intno = s->irq_base + irq;
     }