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Index: sys/kern/subr_bus.c
===================================================================
--- sys/kern/subr_bus.c
+++ sys/kern/subr_bus.c
@@ -3708,7 +3708,11 @@
if (dev->state != DS_ATTACHED)
return (EBUSY);
- TAILQ_FOREACH(child, &dev->children, link) {
+ /*
+ * Detach children in the revers order.
+ * See bus_generic_suspend for details.
+ */
+ TAILQ_FOREACH_REVERSE(child, &dev->children, device_list, link) {
if ((error = device_detach(child)) != 0)
return (error);
}
@@ -3728,7 +3732,11 @@
{
device_t child;
- TAILQ_FOREACH(child, &dev->children, link) {
+ /*
+ * Shut down children in the revers order.
+ * See bus_generic_suspend for details.
+ */
+ TAILQ_FOREACH_REVERSE(child, &dev->children, device_list, link) {
device_shutdown(child);
}
@@ -3781,15 +3789,23 @@
bus_generic_suspend(device_t dev)
{
int error;
- device_t child, child2;
+ device_t child;
- TAILQ_FOREACH(child, &dev->children, link) {
+ /*
+ * Suspend children in the revers order.
+ * For most buses all children are equal, so the order does not matter.
+ * Other buses, such as acpi, carefully order their child devices to
+ * express implicit dependencies between them. For such buses it is
+ * safer to bring down devices in the reverse order.
+ */
+ TAILQ_FOREACH_REVERSE(child, &dev->children, device_list, link) {
error = BUS_SUSPEND_CHILD(dev, child);
- if (error) {
- for (child2 = TAILQ_FIRST(&dev->children);
- child2 && child2 != child;
- child2 = TAILQ_NEXT(child2, link))
- BUS_RESUME_CHILD(dev, child2);
+ if (error != 0) {
+ child = TAILQ_NEXT(child, link);
+ if (child != NULL) {
+ TAILQ_FOREACH_FROM(child, &dev->children, link)
+ BUS_RESUME_CHILD(dev, child);
+ }
return (error);
}
}

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