regmap: flat: Add flat cache type

While for I2C and SPI devices the overhead of using rbtree for devices with
only one block of registers is negligible the same isn't always going to
be true for MMIO devices where the I/O costs are very much lower. Cater
for these devices by adding a simple flat array type for them where the
lookups are simple array accesses, taking us right back to the original
ASoC cache implementation.

Thanks to Magnus Damm for the discussion which prompted this.

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

1 files changed, 2 insertions, 1 deletions

diff --git a/include/linux/regmap.h b/include/linux/regmap.h
index b7e95bf942c..390d879d473 100644
--- a/include/linux/regmap.h
+++ b/include/linux/regmap.h
@@ -28,7 +28,8 @@ struct regmap_range_cfg;
 enum regcache_type {
 	REGCACHE_NONE,
 	REGCACHE_RBTREE,
-	REGCACHE_COMPRESSED
+	REGCACHE_COMPRESSED,
+	REGCACHE_FLAT,
 };
 
 /**