Re: [Qemu-devel] q35 and sysbus devices

[Eduardo Habkost <ehabkost@redhat.com>]

On Fri, Mar 24, 2017 at 05:08:56PM +0000, Peter Maydell wrote:
> On 24 March 2017 at 16:58, Markus Armbruster <armbru@redhat.com> wrote:
> > "Sysbus" isn't a bus.  In qdev's original design, every device had to
> > plug into a bus, period.  The ones that really didn't were made to plug
> > into "sysbus".
> >
> > Pretty much the only thing "sysbus" devices had in common was that they
> > couldn't be used with device_add and device_del.
> 
> This isn't really true. Sysbus devices support having MMIO regions
> and IRQ lines and GPIO lines. If you need those you're a
> sysbus device; otherwise you can probably just be a plain old Device.
> 
> > We fixed the design to permit bus-less devices, but we didn't get rid of
> > "sysbus".
> 
> Call it what you want, but we should have some common code support
> for "I want to have MMIOs and IRQs and GPIO lines". You could
> argue for moving all that into Device I suppose.

Even if we don't move all that into Device, this sounds like an
argument for the existence of struct SysBusDevice. But I still
don't understand the reason TYPE_SYSTEM_BUS still exists.

-- 
Eduardo