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>

1 files changed, 5 insertions, 4 deletions

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);