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

[Cédric Le Goater]

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 <address@hidden>
> 
> [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. When the sPAPRXive object is instantiated, 
we use xics_max_server_number() to get the max number of cpus
provisioned.

C.