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Subject[PATCH] regmap: Suppress noop writes in regmap_update_bits()
Date
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>
---
drivers/base/regmap/regmap.c | 9 +++++----
1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index e533368..10ecbba3 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);
--
1.7.7.3


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