Re: [Qemu-devel] [RFC PATCH v2 01/21] ppc/xive: introduce a skeleton for the sPAPR XIVE interrupt controller

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Sep 19, 2017 at 03:15:44PM +0200, Cédric Le Goater wrote:
> On 09/19/2017 04:27 AM, David Gibson wrote:
> > On Mon, Sep 11, 2017 at 07:12:15PM +0200, Cédric Le Goater wrote:
> >> Start with a couple of attributes for the XIVE sPAPR controller
> >> model. The number of provisionned IRQ is necessary to size the
> >> different internal XIVE tables, the number of CPUs is also.
> >>
> >> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> > 
> > [snip]
> > 
> >> +static void spapr_xive_realize(DeviceState *dev, Error **errp)
> >> +{
> >> +    sPAPRXive *xive = SPAPR_XIVE(dev);
> >> +
> >> +    if (!xive->nr_targets) {
> >> +        error_setg(errp, "Number of interrupt targets needs to be greater 0");
> >> +        return;
> >> +    }
> >> +    /* We need to be able to allocate at least the IPIs */
> >> +    if (!xive->nr_irqs || xive->nr_irqs < xive->nr_targets) {
> >> +        error_setg(errp, "Number of interrupts too small");
> >> +        return;
> >> +    }
> >> +}
> >> +
> >> +static Property spapr_xive_properties[] = {
> >> +    DEFINE_PROP_UINT32("nr-irqs", sPAPRXive, nr_irqs, 0),
> >> +    DEFINE_PROP_UINT32("nr-targets", sPAPRXive, nr_targets, 0),
> > 
> > I'm a bit uneasy about the number of targets having to be set in
> > advance: this can make life awkward when CPUs are hotplugged.  I know
> > there's something similar in xics, but it has caused some hassles, and
> > we're starting to move away from it.
> > 
> > Do you really need this?
> > 
> 
> Some of the internal table size depend on the number of cpus 
> defined for the machine.

Which ones?  My impression was that there needed to be at least #cpus
* #priority-levels EQs, but there could be more than that, so it was
no longer as tightly bound to the number if "interrupt servers" as xics.

> When the sPAPRXive object is instantiated, 
> we use xics_max_server_number() to get the max number of cpus
> provisioned.
> 
> C.
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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