Re: [Xen-devel] [PATCH] have architectures specify the number of PIRQs a hardware domain gets

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2014-12-05 at 14:51 +0000, Ian Campbell wrote:
> On Fri, 2014-12-05 at 14:48 +0000, Jan Beulich wrote:
> > >>> On 05.12.14 at 15:27, <Ian.Campbell@xxxxxxxxxxxxx> wrote:
> > > On Fri, 2014-12-05 at 13:51 +0000, Jan Beulich wrote:
> > >>  #define nr_static_irqs NR_IRQS
> > >> +#define arch_hwdom_irqs(domid) NR_IRQS
> > > 
> > > FWIW gic_number_lines() is the ARM equivalent of getting the number of
> > > GSIs.
> > > 
> > > *BUT* we don't actually use pirqs on ARM (everything goes via the
> > > virtualised interrupt controller). So maybe we should be setting
> > > nr_pirqs to 0 on ARM. I appreciate you likely want such a patch to come
> > > from an ARM person, so I'm fine with you making this NR_IRQS in the
> > > meantime.
> > 
> > Considering Julien also asking for this, I don't mind changing this to
> > zero for ARM. Just let me know which way I can get this ack-ed.
> 
> If you are happy to provide a version using zero and Julien wants to
> provide a tested-by then I'm fine with going that way.

Seems like things were more complex than Julien expected here, so I
think changing to zero would be a mistake at this point.

AIUI this patch results in no functional change for ARM, in that dom0
previously saw:
        d->nr_pirqs = nr_static_irqs + extra_dom0_irqs;
where nr_static_irqs == NR_IRQS on ARM where now it sees:

When extra_dom0_irqs > 0
        nr_static_irqs + extra_dom0_irqs
which is the same as before. Or when extra_dom0_irqs:
        arch_hwdom_irqs(domid);
==   NR_IRQS
==   nr_static_irqs + 0
i.e. no change.

Oh, actually extra_dom0_irqs has changed from a default of 256 to 0, I
don't think NR_IRQS(1024) + 256 made much sense on ARM (which is limited
to 1020 IRQs in h/w anyway), so I don't consider that a problem.

If that's all correct then: 
        Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

Also Ack with my REST maintainer hat on for the general principal/common
code.

Ian.


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