spapr: introduce a fixed IRQ number space

This proposal introduces a new IRQ number space layout using static
numbers for all devices, depending on a device index, and a bitmap
allocator for the MSI IRQ numbers which are negotiated by the guest at
runtime.

As the VIO device model does not have a device index but a "reg"
property, we introduce a formula to compute an IRQ number from a "reg"
value. It should minimize most of the collisions.

The previous layout is kept in pre-3.1 machines raising the
'legacy_irq_allocation' machine class flag.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 60 insertions, 6 deletions

diff --git a/hw/ppc/spapr_vio.c b/hw/ppc/spapr_vio.c
index be9af71437..840d4a3c45 100644
--- a/hw/ppc/spapr_vio.c
+++ b/hw/ppc/spapr_vio.c
@@ -37,12 +37,13 @@
 
 #include "hw/ppc/spapr.h"
 #include "hw/ppc/spapr_vio.h"
-#include "hw/ppc/xics.h"
 #include "hw/ppc/fdt.h"
 #include "trace.h"
 
 #include <libfdt.h>
 
+#define SPAPR_VIO_REG_BASE 0x71000000
+
 static void spapr_vio_get_irq(Object *obj, Visitor *v, const char *name,
                               void *opaque, Error **errp)
 {
@@ -445,6 +446,55 @@ static void spapr_vio_busdev_reset(DeviceState *qdev)
     }
 }
 
+/*
+ * The register property of a VIO device is defined in livirt using
+ * 0x1000 as a base register number plus a 0x1000 increment. For the
+ * VIO tty device, the base number is changed to 0x30000000. QEMU uses
+ * a base register number of 0x71000000 and then a simple increment.
+ *
+ * The formula below tries to compute a unique index number from the
+ * register value that will be used to define the IRQ number of the
+ * VIO device.
+ *
+ * A maximum of 256 VIO devices is covered. Collisions are possible
+ * but they will be detected when the IRQ is claimed.
+ */
+static inline uint32_t spapr_vio_reg_to_irq(uint32_t reg)
+{
+    uint32_t irq;
+
+    if (reg >= SPAPR_VIO_REG_BASE) {
+        /*
+         * VIO device register values when allocated by QEMU. For
+         * these, we simply mask the high bits to fit the overall
+         * range: [0x00 - 0xff].
+         *
+         * The nvram VIO device (reg=0x71000000) is a static device of
+         * the pseries machine and so is always allocated by QEMU. Its
+         * IRQ number is 0x0.
+         */
+        irq = reg & 0xff;
+
+    } else if (reg >= 0x30000000) {
+        /*
+         * VIO tty devices register values, when allocated by livirt,
+         * are mapped in range [0xf0 - 0xff], gives us a maximum of 16
+         * vtys.
+         */
+        irq = 0xf0 | ((reg >> 12) & 0xf);
+
+    } else {
+        /*
+         * Other VIO devices register values, when allocated by
+         * livirt, should be mapped in range [0x00 - 0xef]. Conflicts
+         * will be detected when IRQ is claimed.
+         */
+        irq = (reg >> 12) & 0xff;
+    }
+
+    return SPAPR_IRQ_VIO | irq;
+}
+
 static void spapr_vio_busdev_realize(DeviceState *qdev, Error **errp)
 {
     sPAPRMachineState *spapr = SPAPR_MACHINE(qdev_get_machine());
@@ -485,10 +535,14 @@ static void spapr_vio_busdev_realize(DeviceState *qdev, Error **errp)
     }
 
     if (!dev->irq) {
-        dev->irq = spapr_irq_findone(spapr, &local_err);
-        if (local_err) {
-            error_propagate(errp, local_err);
-            return;
+        dev->irq = spapr_vio_reg_to_irq(dev->reg);
+
+        if (SPAPR_MACHINE_GET_CLASS(spapr)->legacy_irq_allocation) {
+            dev->irq = spapr_irq_findone(spapr, &local_err);
+            if (local_err) {
+                error_propagate(errp, local_err);
+                return;
+            }
         }
     }
 
@@ -557,7 +611,7 @@ VIOsPAPRBus *spapr_vio_bus_init(void)
     /* Create bus on bridge device */
     qbus = qbus_create(TYPE_SPAPR_VIO_BUS, dev, "spapr-vio");
     bus = SPAPR_VIO_BUS(qbus);
-    bus->next_reg = 0x71000000;
+    bus->next_reg = SPAPR_VIO_REG_BASE;
 
     /* hcall-vio */
     spapr_register_hypercall(H_VIO_SIGNAL, h_vio_signal);