[PATCH 1/2] hw/m68k/q800: Don't connect two qemu_irqs directly to the same input

[Peter Maydell <peter.maydell@linaro.org>]

The q800 board code connects both of the IRQ outputs of the ESCC
to the same pic[3] qemu_irq. Connecting two qemu_irqs outputs directly
to the same input is not valid as it produces subtly wrong behaviour
(for instance if both the IRQ lines are high, and then one goes
low, the PIC input will see this as a high-to-low transition
even though the second IRQ line should still be holding it high).

This kind of wiring needs an explicitly created OR gate; add one.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 hw/m68k/q800.c  | 12 ++++++++++--
 hw/m68k/Kconfig |  1 +
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/hw/m68k/q800.c b/hw/m68k/q800.c
index ce4b47c3e34..dc13007aaf2 100644
--- a/hw/m68k/q800.c
+++ b/hw/m68k/q800.c
@@ -28,6 +28,7 @@
 #include "hw/hw.h"
 #include "hw/boards.h"
 #include "hw/irq.h"
+#include "hw/or-irq.h"
 #include "elf.h"
 #include "hw/loader.h"
 #include "ui/console.h"
@@ -171,6 +172,7 @@ static void q800_init(MachineState *machine)
     CPUState *cs;
     DeviceState *dev;
     DeviceState *via_dev;
+    DeviceState *escc_orgate;
     SysBusESPState *sysbus_esp;
     ESPState *esp;
     SysBusDevice *sysbus;
@@ -283,8 +285,14 @@ static void q800_init(MachineState *machine)
     qdev_prop_set_uint32(dev, "chnAtype", 0);
     sysbus = SYS_BUS_DEVICE(dev);
     sysbus_realize_and_unref(sysbus, &error_fatal);
-    sysbus_connect_irq(sysbus, 0, pic[3]);
-    sysbus_connect_irq(sysbus, 1, pic[3]);
+
+    /* Logically OR both its IRQs together */
+    escc_orgate = DEVICE(object_new(TYPE_OR_IRQ));
+    object_property_set_int(OBJECT(escc_orgate), "num-lines", 2, &error_fatal);
+    qdev_realize_and_unref(escc_orgate, NULL, &error_fatal);
+    sysbus_connect_irq(sysbus, 0, qdev_get_gpio_in(escc_orgate, 0));
+    sysbus_connect_irq(sysbus, 1, qdev_get_gpio_in(escc_orgate, 1));
+    qdev_connect_gpio_out(DEVICE(escc_orgate), 0, pic[3]);
     sysbus_mmio_map(sysbus, 0, SCC_BASE);
 
     /* SCSI */
diff --git a/hw/m68k/Kconfig b/hw/m68k/Kconfig
index c757e7dfa48..60d7bcfb8f2 100644
--- a/hw/m68k/Kconfig
+++ b/hw/m68k/Kconfig
@@ -22,3 +22,4 @@ config Q800
     select ESCC
     select ESP
     select DP8393X
+    select OR_IRQ
-- 
2.20.1