[PATCH 1/1] genirq: outline lazy disable in kerneldoc of irq_disable function.

[Andreas Fenkart <andreas.fenkart@streamunlimited.com>]

comment based on changelog of d209a699a0b975ad

Signed-off-by: Andreas Fenkart <andreas.fenkart@streamunlimited.com>
---
 kernel/irq/chip.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index cbd97ce..4e3c439 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -213,6 +213,19 @@ void irq_enable(struct irq_desc *desc)
 	irq_state_clr_masked(desc);
 }
 
+/**
+ * irq_disable - mask interupt disabled
+ * @desc:		irq descriptor which should be disabled
+ *
+ * If the chip does not implement the irq_disable callback, we
+ * use a lazy disable approach. That means we mark the interrupt
+ * disabled, but leave the hardware unmasked. That's an
+ * optimization because we avoid the hardware access for the
+ * common case where no interrupt happens after we marked it
+ * disabled. If an interrupt happens, then the interrupt flow
+ * handler masks the line at the hardware level and marks it
+ * pending.
+ */
 void irq_disable(struct irq_desc *desc)
 {
 	irq_state_set_disabled(desc);
-- 
1.7.10.4