Re: [Qemu-devel] [PATCH 0/8] Add virtio-mmio and use it in vexpress

[Peter Maydell <peter.maydell@linaro.org>]

On 8 July 2013 13:59, Alexander Graf <agraf@suse.de> wrote:
> On 08.07.2013, at 14:57, Alexander Graf wrote:
>> On 27.06.2013, at 15:04, Peter Maydell wrote:
>>> The basic idea is that the board instantiates some transports,
>>
>> I really dislike that idea. Couldn't you also create a new
>> bus for your vexpress platform and add a virtio-mmio-vexpress
>> device that automatically allocates an interrupt from the main
>> PIC on instantiation? That way you could create transports
>> using -device.

This doesn't seem to gain anything except that the user has
to use -device twice rather than once.

>> Combine that with automatic fdt generation and you get fully
>> command line scaling device creation.
>
> Ah, you already have the fdt generation bit. So you're really
> only missing the automatic irq allocation to make it actually
> user friendly and flexible.

It's not clear to me how you can automatically allocate an IRQ:
there just aren't that many available, and I'm already a bit
nervous about stealing 4, because we might run into issues if
newer versions of h/w use those IRQs for something else. One
approach would be to have all virtio transports share an IRQ
line (the spec currently forbids this; I need to test if it
would actually work in practice...)

As far as I know there's no way to find out at board
construction how many virtio devices you might want.

thanks
-- PMM