Re: [Qemu-devel] [PATCH v3 1/6] hw/misc/dyn_sysbus_binding: helpers for sysbus device dynamic binding

[Paolo Bonzini]

Il 10/09/2014 11:31, Alexander Graf ha scritto:
>> > Yeah, please do the registration in sysbus.c, not in virt.c.  There is
>> > no reason to make the platform_bus_init_notify+DynSysbusNotifier
>> > interface public.  The code in sysbus.c can fill in the fields.
> Sysbus != Platform bus. Sysbus is an in-QEMU representation of a
> pseudo-bus that we put all devices onto that we consider unsorted.
> 
> Platform bus is a machine representation of an actual bus that devices
> are attached to. These devices usually are sysbus devices.

Is there any difference between the two?

Take a machine that has two chips, a SoC that does everything except
USB, and a USB controller chip.

Strictly speaking the USB controller chip would be on a "platform bus",
but we would likely put it on sysbus.

Why should it matter whether the devices are static or dynamic, for the
sake of calling something the "system" or the "platform" bus?  I would
say that QEMU calls "sysbus" the platform bus.

Some devices (e.g. the local APIC in x86, or the in-core timers and GIC
in ARM) should probably not be in sysbus at all, and should attach
directly to the CPU address space.  But that is a quirk in the modeling
of those devices, it shouldn't mean that sysbus is not a "platform" bus.

Paolo