Re: [Xen-devel] [Draft D] Xen on ARM vITS Handling

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-06-05 at 21:25 +0530, Vijay Kilari wrote:
> Let xen mark those phantom devices added using MAPD as dummy and
> just emulate and does not translate ITS commands for these devices.

But we think guests might use this mechanism to drive completion
(instead of polling), so we have to translate INT commands for such
devices, don't we? Otherwise such guests won't work.

> >> So deviceid of any MAPD command for all the guests should be have been
> >> within pre-identified list.
> >
> > I don't think that is true for a domU, not necessarily for a dom0 given
> > that any device id can be used with INT.
> 
>    If the INT command is with valid device (not phantom) then Xen can 
> translate
> and send to ITS hardware

That is not what this design says, Xen will translate and call
vgic_interrupt_inject, which doesn't go via the hardware ITS at all,
since it doesn't need to.

[...]
> Sorry. I correct it as "So effectively no physical commands are sent
> to ITS hardware that are related to dummy/phantom devices"

Remember that in this design the vits doesn't generate any commands to
the physical its _at all_ even for real devices. It just calls
core/generic APIs.

Ian.


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