Realize methods realizing "sideways" in the composition tree

[Markus Armbruster <armbru@redhat.com>]

Perhaps I'm slow on the uptake today...

We have

    typedef struct XHCIPciState {
        /*< private >*/
        PCIDevice parent_obj;
        /*< public >*/
(1)     XHCIState xhci;
        OnOffAuto msi;
        OnOffAuto msix;
    } XHCIPciState;

This is a PCI device that contains a (bus-less) TYPE_XHCI device, at
(1).

    static void xhci_instance_init(Object *obj)
    {
        XHCIPciState *s = XHCI_PCI(obj);
        /*
         * QEMU_PCI_CAP_EXPRESS initialization does not depend on QEMU command
         * line, therefore, no need to wait to realize like other devices
         */
        PCI_DEVICE(obj)->cap_present |= QEMU_PCI_CAP_EXPRESS;
(2)     object_initialize_child(obj, "xhci-core", &s->xhci, TYPE_XHCI);
        qdev_alias_all_properties(DEVICE(&s->xhci), obj);
    }

The .instance_init() method initializes the child as it should, at (2).

    static void usb_xhci_pci_realize(struct PCIDevice *dev, Error **errp)
    {
        int ret;
        Error *err = NULL;
        XHCIPciState *s = XHCI_PCI(dev);

        [a few dev->config[] modifications...]

(1)     object_property_set_link(OBJECT(&s->xhci), "host", OBJECT(s), NULL);
        s->xhci.intr_update = xhci_pci_intr_update;
        s->xhci.intr_raise = xhci_pci_intr_raise;
(2)     object_property_set_bool(OBJECT(&s->xhci), "realized", true, &err);
        if (err) {
            error_propagate(errp, err);
            return;
        }

The .realize() method realizes the child at (1).  It should use
qdev_realize() like we do everywhere else, since commit ce189ab230
"qdev: Convert bus-less devices to qdev_realize() with Coccinelle".

It sets a link property from the child back to the parent at (2).  Why
do we need a link?  Each QOM Object contains a pointer to its parent,
doesn't it?

Same for xhci_sysbus_realize().