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 <[email protected]> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
