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.

---
 drivers/base/regmap/Makefile        |    2 +-
 drivers/base/regmap/internal.h      |    1 +
 drivers/base/regmap/regcache-flat.c |   72 +++++++++++++++++++++++++++++++++++
 drivers/base/regmap/regcache.c      |    1 +
 include/linux/regmap.h              |    3 +-
 5 files changed, 77 insertions(+), 2 deletions(-)
 create mode 100644 drivers/base/regmap/regcache-flat.c

index 5e75d1b..cf12998 100644
@@ -1,5 +1,5 @@
 obj-$(CONFIG_REGMAP) += regmap.o regcache.o
-obj-$(CONFIG_REGMAP) += regcache-rbtree.o regcache-lzo.o
+obj-$(CONFIG_REGMAP) += regcache-rbtree.o regcache-lzo.o regcache-flat.o
 obj-$(CONFIG_DEBUG_FS) += regmap-debugfs.o
 obj-$(CONFIG_REGMAP_I2C) += regmap-i2c.o
 obj-$(CONFIG_REGMAP_SPI) += regmap-spi.o

index 401d191..e22bb80 100644
@@ -177,5 +177,6 @@ int regcache_lookup_reg(struct regmap *map, unsigned int reg);
 
 extern struct regcache_ops regcache_rbtree_ops;
 extern struct regcache_ops regcache_lzo_ops;
+extern struct regcache_ops regcache_flat_ops;
 
 #endif

index 835883b..e69ff3e 100644
@@ -22,6 +22,7 @@
 static const struct regcache_ops *cache_types[] = {
 	&regcache_rbtree_ops,
 	&regcache_lzo_ops,
+	&regcache_flat_ops,
 };
 
 static int regcache_hw_init(struct regmap *map)

index b7e95bf..390d879 100644
@@ -28,7 +28,8 @@ struct regmap_range_cfg;
 enum regcache_type {
 	REGCACHE_NONE,
 	REGCACHE_RBTREE,
-	REGCACHE_COMPRESSED
+	REGCACHE_COMPRESSED,
+	REGCACHE_FLAT,
 };
 
 /**

1.7.10.4