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.
Signed-off-by: Michael Bohan <mbohan@xxxxxxxxxxxxxx>
---
arch/arm/include/asm/mach/arch.h | 2 +-
arch/arm/kernel/irq.c | 14 ++++++++++++--
2 files changed, 13 insertions(+), 3 deletions(-)
diff --git a/arch/arm/include/asm/mach/arch.h b/arch/arm/include/asm/mach/arch.h
index d7692ca..cc6506a 100644
--- a/arch/arm/include/asm/mach/arch.h
+++ b/arch/arm/include/asm/mach/arch.h
@@ -22,7 +22,7 @@ struct machine_desc {
const char *const *dt_compat; /* array of device tree
* 'compatible' strings */
- unsigned int nr_irqs; /* number of IRQs */
+ int nr_irqs; /* number of IRQs */
#ifdef CONFIG_ZONE_DMA
unsigned long dma_zone_size; /* size of DMA-able area */
diff --git a/arch/arm/kernel/irq.c b/arch/arm/kernel/irq.c
index 3efd82c..f74b173 100644
--- a/arch/arm/kernel/irq.c
+++ b/arch/arm/kernel/irq.c
@@ -129,8 +129,18 @@ void __init init_IRQ(void)
#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
--
1.7.8.3
--
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