Re: [Qemu-devel] [PATCH RFC 0/3] basic support for composing sysbus devices

[Jan Kiszka]

On 2011-06-08 13:33, Peter Maydell wrote:
> At the moment you can't really implement one sysbus device by saying
> that it's composed of a set of other sysbus devices. This patch adds
> new functions sysbus_pass_mmio() and sysbus_pass_one_irq() which
> allow a sysbus device to delegate an MMIO or IRQ to another sysbus
> device (The approach is inspired by the existing sysbus_pass_irq()
> which lets a sysbus device delegate all its IRQs at once).
> 
> This works; the most obvious deficiency is that the subcomponent
> device will still appear as its own device on the bus.
> 
> So: is this a reasonable solution to the problem, or an unacceptable
> hack? Comments welcome :-)

Sounds more like a little hack. :)

The relationships should be expressed via qdev, not yet another
sysbus-specific extension. Generally, many services of sysbus should
rather be generic qdev things.

Is there anything that today prevents creating a local bus and attaching
the component devices to that? If it's multi-bus support, that should to
be added anyway. Passing-through of MMIO and IRQs is still a worthwhile
generic service, then probably qbus associated.

Jan

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