Re: [Qemu-ppc] [PATCH 0/9] Add platform bus

[Paolo Bonzini]

Il 22/07/2013 20:21, Peter Maydell ha scritto:
>> > Platforms without ISA and/or PCI have had a seriously hard time in the 
>> > dynamic
>> > device creation world of QEMU. Devices on these were modeled as SysBus 
>> > devices
>> > which can only be instantiated in machine files, not through -device.
>> >
>> > Why is that so?
> Because you can't as a user of this sort of hardware
> plug in an extra serial port to a SoC, because there's just nowhere
> to plug it in. So why should it be possible to plug an extra
> serial port into the QEMU model of the SoC?

And why exactly should QEMU be limited to modeling an existing SoC?

Perhaps the user is not working with an existing SoC.  They are working
with with IP building blocks that they can combine the way they prefer,
and they haven't yet made up their mind on the exact set of devices
they'll have.  (because not all the world is a PC, but then not all the
non-PC world is ARM either).

Perhaps the user is working on kernel support for device tree / ACPI,
wants to test many device combinations, and does not want to touch C
code in order to do that.

Perhaps the user can plug daughterboards that connect to the SoC and add
an extra serial port, visible as yet another MMIO device.

> And why should
> the user of QEMU have to know very low hardware level detail
> like what a particular devboard's IRQ and memory map are?

Of course in some scenarios the user of QEMU doesn't need them, but
there are many kinds of users...

Paolo