diff --git a/drivers/irqchip/irq-crossbar.c b/drivers/irqchip/irq-crossbar.c
index a8c615692803..518d712c475a 100644
--- a/drivers/irqchip/irq-crossbar.c
+++ b/drivers/irqchip/irq-crossbar.c
@@ -89,6 +89,17 @@ static int crossbar_domain_map(struct irq_domain *d, unsigned int irq,
 	return 0;
 }
 
+/**
+ * crossbar_domain_unmap - unmap a crossbar<->irq connection
+ * @d: domain of irq to unmap
+ * @irq: virq number
+ *
+ * We do not maintain a use count of total number of map/unmap
+ * calls for a particular irq to find out if a irq can be really
+ * unmapped. This is because unmap is called during irq_dispose_mapping(irq),
+ * after which irq is anyways unusable. So an explicit map has to be called
+ * after that.
+ */
 static void crossbar_domain_unmap(struct irq_domain *d, unsigned int irq)
 {
 	irq_hw_number_t hw = irq_get_irq_data(irq)->hwirq;