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Re: [Xen-devel] [RFC PATCH v1 10/10] xen/arm: GICv3 device tree parsing

On 03/25/2014 12:33 PM, Julien Grall wrote:
> On 03/25/2014 11:04 AM, Stefano Stabellini wrote:
>> On Mon, 24 Mar 2014, Julien Grall wrote:
>>> Hi Stefano,
>>> On 24/03/14 17:34, Stefano Stabellini wrote:
>>>> I think that for Dom0 we have to use vgic_v3, because it doesn't only
>>>> give you support for more vcpus but also MSI and MSI-X delivery.
>>> Right.
>>>> For DomUs it might be important to support vgic_v2 on gicv3 hardware,
>>>> however I wouldn't want to defer the decision to the user (i.e.
>>>> introduce yet another VM config option), if not for debugging.
>>>> Would it be possible to advirtise both gicv2 and gicv3 on device tree?
>>>> What would the guest kernel do in that case?
>>> Linux will try to load both GICv2 and GICv3 drivers. In any case I don't 
>>> think
>>> it's a solution because:
>>>     - you don't know how the kernel will react
>>>         - how will you choose which backend to use?
>>>> Otherwise we could default to vgic_v2 if vcpus <= 8 and vgic_v3 if
>>>> vcpus > 8.
>>> What about kernel which only support GICv3 and have less than 8 VCPUS?
>>> What about of device (MSI, ...) passthrough with this kind of kernel?
>>> I think we need to have a VM config option in this specific case.
>> Having a VM config option is OK, but it should be the last resort for
>> people doing something very uncommon.
>> GICv3 support in Linux and distros is probably going to be widespread
>> soon, so we might not have to worry about it though.
> I don't think GICv3 will supported in 3.15. The current series doesn't
> support GICv3 on 32 bits
> (http://www.spinics.net/lists/arm-kernel/msg317028.html).
> But, I'm more worry about other OS than Linux (e.g FreeRTOS, *BSD,...)
> which may not support GICv2 before a while.

I should have write GICv3.

Julien Grall

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