[11/22] cbus: retu: IRQ demux optimization

Commit Message

Felipe Balbi July 11, 2011, 11:17 a.m. UTC

it's definitely not always that we will have
all 16 interrupts fired at the same time, so
in order to avoid looping so many times, we
are now using ffs() which is implemented
(on ARM) using the far better clz instruction.

This will save us quite some loops and could
improve IRQ latency on Retu significantly
(no actual measurements were made, though)

Signed-off-by: Felipe Balbi <[e-mail]>
---
 drivers/cbus/retu.c |   14 ++++++++------
 1 files changed, 8 insertions(+), 6 deletions(-)

Patch

diff --git a/drivers/cbus/retu.c b/drivers/cbus/retu.c
index b7fbd18..e749c0e 100644
--- a/drivers/cbus/retu.c
+++ b/drivers/cbus/retu.c
@@ -36,6 +36,8 @@ 
 #include <linux/platform_device.h>
 #include <linux/platform_data/cbus.h>
 
+#include <asm/bitops.h>
+
 #include "cbus.h"
 #include "retu.h"
 
@@ -183,8 +185,6 @@  static irqreturn_t retu_irq_handler(int irq, void *_retu)
 {
 	struct retu		*retu = _retu;
 
-	int			i;
-
 	u16			idr;
 	u16			imr;
 
@@ -199,11 +199,13 @@  static irqreturn_t retu_irq_handler(int irq, void *_retu)
 		return IRQ_NONE;
 	}
 
-	for (i = retu->irq_base; idr != 0; i++, idr >>= 1) {
-		if (!(idr & 1))
-			continue;
+	while (idr) {
+		unsigned long	pending = __ffs(idr);
+		unsigned int	irq;
 
-		handle_nested_irq(i);
+		idr &= ~BIT(pending);
+		irq = pending + retu->irq_base;
+		handle_nested_irq(irq);
 	}
 
 	return IRQ_HANDLED;