[tip:irq/core] genirq: Add kerneldoc for irq_disable.

[tip-bot for Andreas Fenkart <tipbot@zytor.com>]

Commit-ID:  d671a605580d2caafc77f1a25bcf8435795df6fe
Gitweb:     http://git.kernel.org/tip/d671a605580d2caafc77f1a25bcf8435795df6fe
Author:     Andreas Fenkart <andreas.fenkart@streamunlimited.com>
AuthorDate: Fri, 10 May 2013 12:21:30 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 29 May 2013 11:09:10 +0200

genirq: Add kerneldoc for irq_disable.

Document the lazy disable functionality. comment based on changelog of
d209a699a0b975ad

Signed-off-by: Andreas Fenkart <andreas.fenkart@streamunlimited.com>
Cc: balbi@ti.com
Link: http://lkml.kernel.org/r/1368181290-1583-1-git-send-email-andreas.fenkart@streamunlimited.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/irq/chip.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index cbd97ce..a3bb14f 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 - Mark 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);