Re: [RFC PATCH v2 13/22] xen/arm: its: Add virtual ITS command support

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

On Mon, 4 May 2015, Vijay Kilari wrote:
> On Thu, Apr 30, 2015 at 7:59 PM, Julien Grall <julien.grall@citrix.com> wrote:
> > Hi,
> >
> > On 30/04/15 14:47, Stefano Stabellini wrote:
> >>>>>
> >>>>> If the devid is not within this range, the ITS won't recognize the value and
> >>>>> won't be able to send the interrupt.
> >>>>>
> >>>>> So this is clearly not the right value.
> >>>>
> >>>> Sure, in that case the maximum value allowed by GITS_TYPER.Devbits.
> >>>> Vijay, what is the value of GITS_TYPER.Devbits on your platform?
> >>>
> >>> It is 21 bits
> >>
> >> I would imagine that 21 bits would be plenty to find an unused devid.
> >>
> >> Alternatively we could use an inexistent function of a real device, such
> >> as 00:00.1 (function 1 of the host bridge).
> >
> > As discussed IRL, this idea sounds good to me.
> >
> > Although I would be happy with any other way which ensure the devid is free.
> 
> Has prototyped with 00.00.1 as device id. But I see that Dom0 boot is
> slow compared to polling mode.

This is very interesting.


> This could be because Dom0 has to keep
> trapping on creader to check if creader is updated or not.

This sounds like a plausible explanation. That's because the guest is
polling, right? I think we should pause the guest vcpu until we receive
the interrupt.

You can do that by calling vcpu_block.