hw/core/qdev: handle parent bus change regarding resettable

In qdev_set_parent_bus(), when changing the parent bus of a
realized device, if the source and destination buses are not in the
same reset state, some adaptations are required. This patch adds
needed call to resettable_change_parent() to make sure a device reset
state stays coherent with its parent bus.

The addition is a no-op if:
1. the device being parented is not realized.
2. the device is realized, but both buses are not under reset.

Case 2 means that as long as qdev_set_parent_bus() is called
during the machine realization procedure (which is before the
machine reset so nothing is in reset), it is a no op.

There are 52 call sites of qdev_set_parent_bus(). All but one fall
into the no-op case:
+ 29 trivial calls related to virtio (in hw/{s390x,display,virtio}/
  {vhost,virtio}-xxx.c) to set a vdev(or vgpu) composing device
  parent bus just before realizing the same vdev(vgpu).
+ hw/core/qdev.c: when creating a device in qdev_try_create()
+ hw/core/sysbus.c: when initializing a device in the sysbus
+ hw/i386/amd_iommu.c: before realizing AMDVIState/pci
+ hw/isa/piix4.c: before realizing PIIX4State/rtc
+ hw/misc/auxbus.c: when creating an AUXBus
+ hw/misc/auxbus.c: when creating an AUXBus child
+ hw/misc/macio/macio.c: when initializing a MACIOState child
+ hw/misc/macio/macio.c: before realizing NewWorldMacIOState/pmu
+ hw/misc/macio/macio.c: before realizing NewWorldMacIOState/cuda
+ hw/net/virtio-net.c: Used for migration when using the failover
                       mechanism to migration a vfio-pci/net. It is
                       a no-op because at this point the device is
                       already on the bus.
+ hw/pci-host/designware.c: before realizing DesignwarePCIEHost/root
+ hw/pci-host/gpex.c: before realizing GPEXHost/root
+ hw/pci-host/prep.c: when initialiazing PREPPCIState/pci_dev
+ hw/pci-host/q35.c: before realizing Q35PCIHost/mch
+ hw/pci-host/versatile.c: when initializing PCIVPBState/pci_dev
+ hw/pci-host/xilinx-pcie.c: before realizing XilinxPCIEHost/root
+ hw/s390x/event-facility.c: when creating SCLPEventFacility/
                             TYPE_SCLP_QUIESCE
+ hw/s390x/event-facility.c: ditto with SCLPEventFacility/
                             TYPE_SCLP_CPU_HOTPLUG
+ hw/s390x/sclp.c: Not trivial because it is called on a SLCPDevice
  just after realizing it. Ok because at this point the destination
  bus (sysbus) is not in reset; the realize step is before the
  machine reset.
+ hw/sd/core.c: Not OK. Used in sdbus_reparent_card(). See below.
+ hw/ssi/ssi.c: Used to put spi slave on spi bus and connect the cs
  line in ssi_auto_connect_slave(). Ok because this function is only
  used in realize step in hw/ssi/aspeed_smc.ci, hw/ssi/imx_spi.c,
  hw/ssi/mss-spi.c, hw/ssi/xilinx_spi.c and hw/ssi/xilinx_spips.c.
+ hw/xen/xen-legacy-backend.c: when creating a XenLegacyDevice device
+ qdev-monitor.c: in device hotplug creation procedure before realize

Note that this commit alone will have no effect, right now there is no
use of resettable API to reset anything. So a bus will never be tagged
as in-reset by this same API.

The one place where side-effect will occurs is in hw/sd/core.c in
sdbus_reparent_card(). This function is only used in the raspi machines,
including during the sysbus reset procedure. This case will be
carrefully handled when doing the multiple phase reset transition.

Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200123132823.1117486-7-damien.hedde@greensocs.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/core/qdev.c

@@ -96,25 +96,31 @@ static void bus_add_child(BusState *bus, DeviceState *child)
 
 void qdev_set_parent_bus(DeviceState *dev, BusState *bus)
 {
-    bool replugging = dev->parent_bus != NULL;
+    BusState *old_parent_bus = dev->parent_bus;
 
-    if (replugging) {
+    if (old_parent_bus) {
         trace_qdev_update_parent_bus(dev, object_get_typename(OBJECT(dev)),
-            dev->parent_bus, object_get_typename(OBJECT(dev->parent_bus)),
+            old_parent_bus, object_get_typename(OBJECT(old_parent_bus)),
             OBJECT(bus), object_get_typename(OBJECT(bus)));
         /*
          * Keep a reference to the device while it's not plugged into
          * any bus, to avoid it potentially evaporating when it is
          * dereffed in bus_remove_child().
+         * Also keep the ref of the parent bus until the end, so that
+         * we can safely call resettable_change_parent() below.
          */
         object_ref(OBJECT(dev));
         bus_remove_child(dev->parent_bus, dev);
-        object_unref(OBJECT(dev->parent_bus));
     }
     dev->parent_bus = bus;
     object_ref(OBJECT(bus));
     bus_add_child(bus, dev);
-    if (replugging) {
+    if (dev->realized) {
+        resettable_change_parent(OBJECT(dev), OBJECT(bus),
+                                 OBJECT(old_parent_bus));
+    }
+    if (old_parent_bus) {
+        object_unref(OBJECT(old_parent_bus));
         object_unref(OBJECT(dev));
     }
 }