arm: irq: Allow for specification of no preallocated irqs
For cases with SPARSE_IRQ enabled, irqs preallocated with
arch_probe_nr_irqs() are already marked as allocated in the
allocated_irqs bitmap. As a consequence, irq chip drivers that
allocate irqs will feel one of two behaviors:
1. An allocation will succeed with the starting irq_base one
more than the preallocated irqs. This will thus waste the
preceeding interrupt resources that were preallocated, unless a
legacy chip driver happens to assume ownership of these by some
platform definition. The GIC driver is a typical primary chip
driver, and abides to the allocation APIs. So this can be a
problem in many trivial usecases.
2. An allocation will fail with < 0. This can also happen in the
GIC driver, which interprets this value as meaning the irq_descs
are already preallocated. But in Device Tree configurations, the
fallback irq_base is -1. This results in an invalid irq_base
value.
Looking forward, we are moving towards a world where preallocation
of irqs is no longer necessary. irq_domain is scoped to handle all
irq_desc allocations in the future. Thus, we should support
configurations where the platform wants to preallocate no irqs.
One easy way to achieve this is to allow for
machine_desc->nr_irqs < 0, which indicates not to preallocate any
interrupts.
Change-Id: Ie793932c58de72c1b91b6e039b77a8e5d64ecc75
Signed-off-by: Michael Bohan <mbohan@codeaurora.org>
diff --git a/arch/arm/kernel/irq.c b/arch/arm/kernel/irq.c
index 4468153..7561081 100644
--- a/arch/arm/kernel/irq.c
+++ b/arch/arm/kernel/irq.c
@@ -134,8 +134,18 @@
#ifdef CONFIG_SPARSE_IRQ
int __init arch_probe_nr_irqs(void)
{
- nr_irqs = machine_desc->nr_irqs ? machine_desc->nr_irqs : NR_IRQS;
- return nr_irqs;
+ /*
+ * machine_desc->nr_irqs < 0 is a special case that
+ * specifies not to preallocate any irq_descs.
+ */
+ if (machine_desc->nr_irqs < 0) {
+ nr_irqs = 0;
+ return nr_irqs;
+ } else {
+ nr_irqs = machine_desc->nr_irqs ?
+ machine_desc->nr_irqs : NR_IRQS;
+ return nr_irqs;
+ }
}
#endif