Re: [PATCH-for-11.0 v6 08/13] hw/sparc64/sun4u: Use fw_cfg_init_io_nodma()

[Zhao Liu <zhao1.liu@intel.com>]

> > > I think maybe one reason to use `ebus` is because...
> > > 
> > > > -    sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), &error_fatal);
> > > > -    memory_region_add_subregion(pci_address_space_io(ebus), BIOS_CFG_IOPORT,
> > >                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > ... because the parent region is managed by ebus.
> > > 
> > > Perhaps we should add another argument: Object *parent?
> > 
> > I thought about it but don't think so, all instances but this one use
> > the machine container.
> > 
> > I'll improve the description.
> 
> The reason that the fw_cfg device lives under ebus on sun4u is because the
> ebus device is effectively a PCI-ISA bridge, and the fw_cfg port is mapped
> into I/O address space along with other ISA devices. I'm not sure that
> setting the parent to the machine is the right thing to do here.

Thanks Philippe and Mark, IIUC, ebus doesn't have the hotplug use case,
so it lives long enough like the sun4u/v machine, therefore replacing
the parent object "ebus" with machine is safe.

And it might be better to explicitly set ebus as not supporting hotplug
(via dc->hotpluggable = false).

Adding a "parent" argument to the generic interface fw_cfg_init_io_nodma()
doesn't seem necessary at the moment, since using the default machine as
parent seems enough to meet all current needs in QEMU.

What do you think?

Regards,
Zhao