From: Mark Brown <broonie@opensource.wolfsonmicro.com>
Date: Fri, 18 Nov 2011 16:03:50 +0000 (+0000)
Subject: regmap: Suppress noop writes in regmap_update_bits()
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=d91e8db2c3bbe8ef0e2f3e1a6ff5b31a8d53ef16;p=linux-beck.git

regmap: Suppress noop writes in regmap_update_bits()

If the new register value is identical to the original one then suppress
the write to the hardware in regmap_update_bits(), saving some I/O cost.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
---

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index e533368e5598..10ecbba32e10 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -583,18 +583,19 @@ int regmap_update_bits(struct regmap *map, unsigned int reg,
 		       unsigned int mask, unsigned int val)
 {
 	int ret;
-	unsigned int tmp;
+	unsigned int tmp, orig;
 
 	mutex_lock(&map->lock);
 
-	ret = _regmap_read(map, reg, &tmp);
+	ret = _regmap_read(map, reg, &orig);
 	if (ret != 0)
 		goto out;
 
-	tmp &= ~mask;
+	tmp = orig & ~mask;
 	tmp |= val & mask;
 
-	ret = _regmap_write(map, reg, tmp);
+	if (tmp != orig)
+		ret = _regmap_write(map, reg, tmp);
 
 out:
 	mutex_unlock(&map->lock);