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for bus suspend, detach and shutdown iterate children in reverse order

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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.

I believe that this is the reason why hpet_suspend had to be disabled.
Some drivers depend on a working event timer until they are suspended.
But previously we would suspend hpet very early.

I tested this change by makinbg hpet_suspend actually stop HPET timers
and tested that too.

Note that this change is not a complete solution as it does not take
into account bus passes.
A better approach would be to track the actual attach order of the
devices and to use the reverse of that.

Reviewed by:	imp, mav
MFC after:	3 weeks
Differential Revision: https://reviews.freebsd.org/D15291
This commit is contained in:
Andriy Gapon 2018-05-05 05:19:32 +00:00
parent 5ec2c93667
commit bd3afae0ca
1 changed files with 25 additions and 9 deletions
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34
sys/kern/subr_bus.c
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@ -3708,7 +3708,11 @@ bus_generic_detach(device_t dev)
if (dev->state != DS_ATTACHED)
return (EBUSY);
TAILQ_FOREACH(child, &dev->children, link) {
/*
* Detach children in the reverse 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 @@ bus_generic_shutdown(device_t dev)
{
device_t child;
TAILQ_FOREACH(child, &dev->children, link) {
/*
* Shut down children in the reverse order.
* See bus_generic_suspend for details.
*/
TAILQ_FOREACH_REVERSE(child, &dev->children, device_list, link) {
device_shutdown(child);
}
@ -3781,15 +3789,23 @@ int
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 reverse 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);
}
}