IRQ affinity masks are not allocated in uniprocessor configurations.
This requires special case non-SMP code in drivers for irqchips which
have per-CPU enable or mask registers.

Since IRQ affinity is always the same in a uniprocessor configuration,
we can provide a correct affinity mask without allocating one per IRQ.

By returning a real cpumask from irq_data_get_affinity_mask even when
SMP is disabled, irqchip drivers which iterate over that mask will
automatically do the right thing.

Signed-off-by: Samuel Holland <>

Changes in v3:
 - Use cpumask_of(0) instead of cpu_possible_mask

 include/linux/irq.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/irq.h b/include/linux/irq.h
index 02073f7a156e..996e22744edd 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -151,7 +151,9 @@ struct irq_common_data {
        void                    *handler_data;
        struct msi_desc         *msi_desc;
+#ifdef CONFIG_SMP
        cpumask_var_t           affinity;
        cpumask_var_t           effective_affinity;
@@ -882,13 +884,19 @@ static inline int irq_data_get_node(struct irq_data *d)
 static inline
 const struct cpumask *irq_data_get_affinity_mask(struct irq_data *d)
+#ifdef CONFIG_SMP
        return d->common->affinity;
+       return cpumask_of(0);
 static inline void irq_data_update_affinity(struct irq_data *d,
                                            const struct cpumask *m)
+#ifdef CONFIG_SMP
        cpumask_copy(d->common->affinity, m);
 static inline const struct cpumask *irq_get_affinity_mask(int irq)

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