[Qemu-devel] [PATCH 4/7] pseries: Emit device tree nodes in reg order

[Alexander Graf <agraf@suse.de>]

From: David Gibson <david@gibson.dropbear.id.au>

Although in theory the device tree has no inherent ordering, in practice
the order of nodes in the device tree does effect the order that devices
are detected by software.

Currently the ordering is determined by the order the devices appear on
the QEMU command line. Although that does give the user control over the
ordering, it is fragile, especially when the user does not generate the
command line manually - eg. when using libvirt etc.

So order the device tree based on the reg value, ie. the address of on
the VIO bus of the devices. This gives us a sane and stable ordering.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>

[agraf] add braces
(cherry picked from commit 05c194384f836240ea4c2da5fa3be43a54bff021)
---
 hw/spapr_vio.c |   50 +++++++++++++++++++++++++++++++++++++++++++++-----
 1 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/hw/spapr_vio.c b/hw/spapr_vio.c
index 2dcc036..8bd00ca 100644
--- a/hw/spapr_vio.c
+++ b/hw/spapr_vio.c
@@ -749,21 +749,61 @@ static void spapr_vio_register_devices(void)
 device_init(spapr_vio_register_devices)
 
 #ifdef CONFIG_FDT
+static int compare_reg(const void *p1, const void *p2)
+{
+    VIOsPAPRDevice const *dev1, *dev2;
+
+    dev1 = (VIOsPAPRDevice *)*(DeviceState **)p1;
+    dev2 = (VIOsPAPRDevice *)*(DeviceState **)p2;
+
+    if (dev1->reg < dev2->reg) {
+        return -1;
+    }
+    if (dev1->reg == dev2->reg) {
+        return 0;
+    }
+
+    /* dev1->reg > dev2->reg */
+    return 1;
+}
+
 int spapr_populate_vdevice(VIOsPAPRBus *bus, void *fdt)
 {
-    DeviceState *qdev;
-    int ret = 0;
+    DeviceState *qdev, **qdevs;
+    int i, num, ret = 0;
 
+    /* Count qdevs on the bus list */
+    num = 0;
     QTAILQ_FOREACH(qdev, &bus->bus.children, sibling) {
-        VIOsPAPRDevice *dev = (VIOsPAPRDevice *)qdev;
+        num++;
+    }
+
+    /* Copy out into an array of pointers */
+    qdevs = g_malloc(sizeof(qdev) * num);
+    num = 0;
+    QTAILQ_FOREACH(qdev, &bus->bus.children, sibling) {
+        qdevs[num++] = qdev;
+    }
+
+    /* Sort the array */
+    qsort(qdevs, num, sizeof(qdev), compare_reg);
+
+    /* Hack alert. Give the devices to libfdt in reverse order, we happen
+     * to know that will mean they are in forward order in the tree. */
+    for (i = num - 1; i >= 0; i--) {
+        VIOsPAPRDevice *dev = (VIOsPAPRDevice *)(qdevs[i]);
 
         ret = vio_make_devnode(dev, fdt);
 
         if (ret < 0) {
-            return ret;
+            goto out;
         }
     }
 
-    return 0;
+    ret = 0;
+out:
+    free(qdevs);
+
+    return ret;
 }
 #endif /* CONFIG_FDT */
-- 
1.6.0.2