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Re: [Qemu-ppc] [PATCH 0/5] Platform device support

From: Alexander Graf
Subject: Re: [Qemu-ppc] [PATCH 0/5] Platform device support
Date: Thu, 19 Jun 2014 23:38:08 +0200
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.6.0

On 19.06.14 22:54, Paolo Bonzini wrote:
Il 04/06/2014 14:28, Alexander Graf ha scritto:

But do we need that level of complexity for normal devices usually? In a
normal platform world (SoCs, PV machines) we have a flat memory layout we
can plug our device memory into. We also have a flat IRQ model where we
can plug our device IRQs into.

So the idea for platform devices arose. A platform device is really just a
device that exposes its qemu_irq slots and memory regions to the world.

That allows us to write machine specific code that maps a platform device wherever the machine thinks fits nicely. It also allows that same machine to generate a device tree entry for platform devices easily, as it is fully
aware of the interrupt lines and places it was mapped to.

A device (read: user) may or may not explictly request to be mapped at a
specific IRQ and/or memory address. If no explicit mapping is requested,
platform devices can get mapped at convenient places by the machine.

The actual pressing issue this solves is that today it's impossible to spawn serial ports from the command line. With this patch set, it's possible to
do so. But it lays the groundwork for much more...

I have more than a suspect that you and Peter Crosthwaite are trying to do the same. I hope that memory region QOMification can get into 2.1, that can be a starting point that we can work from.

The major difference between the two of us is that Peter wants to have the user specify everything on the command line so he can build a VM from the device tree description of a system.

I want to make sure the user does not have to specify anything that could go wrong on the command line, similar to how he can just use -device pci-dev today. The more we automatically allocate for him, the less can go wrong.


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