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pci: fix 'hotplugglable' property behavior

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Currently the property may flip its state
during VM bring up or just doesn't work as
the name implies.

In particular with PCIE root port that has
'hotplug={on|off}' property, and when it's
turned off, one would expect
  'hotpluggable' == false
for any devices attached to it.
Which is not the case since qbus_is_hotpluggable()
used by the property just checks for presence
of any hotplug_handler set on bus.

The problem is that name BusState::hotplug_handler
from its inception is misnomer, as it handles
not only hotplug but also in many cases coldplug
as well (i.e. generic wiring interface), and
it's fine to have hotplug_handler set on bus
while it doesn't support hotplug (ex. pcie-slot
with hotplug=off).

Another case of root port flipping 'hotpluggable'
state when ACPI PCI hotplug is enabled in this
case root port with 'hotplug=off' starts as
hotpluggable and then later on, pcihp
hotplug_handler clears hotplug_handler
explicitly after checking root port's 'hotplug'
property.

So root-port hotpluggablity check sort of works
if pcihp is enabled but is broken if pcihp is
disabled.

One way to deal with the issue is to ask
hotplug_handler if bus it controls is hotpluggable
or not. To do that add is_hotpluggable_bus()
hook to HotplugHandler interface and use it in
'hotpluggable' property + teach pcie-slot to
actually look into 'hotplug' property state
before deciding if bus is hotpluggable.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20230302161543.286002-13-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Igor Mammedov 2023-03-02 17:15:21 +01:00 • committed by Michael S. Tsirkin
parent f40e6a4cc1
commit ceefa0b746
3 changed files with 22 additions and 1 deletions
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13
include/hw/qdev-core.h
View file

@ -812,7 +812,18 @@ void qbus_set_bus_hotplug_handler(BusState *bus);
static inline bool qbus_is_hotpluggable(BusState *bus)
{
return bus->hotplug_handler;
HotplugHandler *plug_handler = bus->hotplug_handler;
bool ret = !!plug_handler;
if (plug_handler) {
HotplugHandlerClass *hdc;
hdc = HOTPLUG_HANDLER_GET_CLASS(plug_handler);
if (hdc->is_hotpluggable_bus) {
ret = hdc->is_hotpluggable_bus(plug_handler, bus);
}
}
return ret;
}
/**