regmap: core: Introduce register stride order

Since the register stride should always equal to 2^N, and bit rotation is
much faster than multiplication and division. So introducing the stride
order and using bit rotation to get the offset of the register from the
index to improve the performance.

Signed-off-by: Xiubo Li <lixiubo@cmss.chinamobile.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/drivers/base/regmap/internal.h b/drivers/base/regmap/internal.h
index 3df9770..c22b04b2 100644
--- a/drivers/base/regmap/internal.h
+++ b/drivers/base/regmap/internal.h
@@ -110,6 +110,7 @@
 	/* number of bits to (left) shift the reg value when formatting*/
 	int reg_shift;
 	int reg_stride;
+	int reg_stride_order;
 
 	/* regcache specific members */
 	const struct regcache_ops *cache_ops;
@@ -263,4 +264,13 @@
 	return map->name;
 }
 
+static inline unsigned int regmap_get_offset(const struct regmap *map,
+					     unsigned int index)
+{
+	if (map->reg_stride_order >= 0)
+		return index << map->reg_stride_order;
+	else
+		return index * map->reg_stride;
+}
+
 #endif