[PATCH] arm: irq: Allow for specification of no preallocated irqs

On Thu, Jan 19, 2012 at 04:29:43PM -0800, Michael Bohan wrote:

On 1/19/2012 3:04 PM, Rob Herring wrote:

quoted

No doubt that arch_probe_nr_irqs is doing the wrong thing on ARM, but no
pre-allocation is not what we want either. We ultimately want
arch_probe_nr_irqs to return NR_IRQS_LEGACY (16) to reserve IRQ0 (aka
NO_IRQ) and legacy ISA IRQs. With my series, NR_IRQS is set to
NR_IRQS_LEGACY for SPARSE_IRQ. You can accomplish the same thing without
that series by setting .nr_irqs to NR_IRQS for non-DT and to
NR_IRQS_LEGACY for DT. For platforms to work in single kernel builds,
they will need to select SPARSE_IRQ.

One issue here is that IRQ_BITMAP_BITS is defined as a function of
NR_IRQS. Currently, there's a hack in place that arbitrarily tacks
on 8196 bits to the end, giving the max virq supported as 8212 with
your patches. Unfortunately, the system I'm running on will require
higher values than that, so this actually breaks me.

Are that many irqs actually going to be in-use at one time?  If not, then the driver should use the irq_domain radix tree reverse map anyway.

g.