Re: [Xen-devel] [PATCH v2] x86/irq: Probe for PIC presence before allocating descs for legacy IRQs

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

On Mon, 16 Nov 2015, Boris Ostrovsky wrote:
> Xen expects legacy interrupts to be there (pretty much for the same reason as
> Hyper-V does) and with this change arch_probe_nr_irqs() returns zero and no
> descriptors are allocated.

Right, because everything which has a PIT gets them and everything
which does not have a PIT does not.

> We can allocate those descriptors as needed in xen_irq_init() (if we know that
> IRQs are legacy), although that would look somewhat ugly and out of place.

Why preallocating them in xen_irq_init()? You simply can remove the
NR_IRQS_LEGACY checks in xen_allocate_irq_gsi/xen_free_irq(), right?

Thanks,

        tglx

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