regmap: allow to define reg_update_bits for no bus configuration

index 21a0c2562ec0..d6fcb45194b0 100644
@@ -876,6 +876,7 @@ struct regmap *__regmap_init(struct device *dev,
 	if (!bus) {
 		map->reg_read  = config->reg_read;
 		map->reg_write = config->reg_write;
+		map->reg_update_bits = config->reg_update_bits;
 
 		map->defer_caching = false;
 		goto skip_format_initialization;

@@ -3064,7 +3065,7 @@ static int _regmap_update_bits(struct regmap *map, unsigned int reg,
 	if (change)
 		*change = false;
 
-	if (regmap_volatile(map, reg) && map->reg_update_bits) {
+	if ((regmap_volatile(map, reg) || !map->bus) && map->reg_update_bits) {
 		ret = map->reg_update_bits(map->bus_context, reg, mask, val);
 		if (ret == 0 && change)
 			*change = true;

index e3c9a25a853a..22652e5fbc38 100644
@@ -290,6 +290,11 @@ typedef void (*regmap_unlock)(void *);
  *		  read operation on a bus such as SPI, I2C, etc. Most of the
  *		  devices do not need this.
  * @reg_write:	  Same as above for writing.
+ * @reg_update_bits: Optional callback that if filled will be used to perform
+ *		     all the update_bits(rmw) operation. Should only be provided
+ *		     if the function require special handling with lock and reg
+ *		     handling and the operation cannot be represented as a simple
+ *		     update_bits operation on a bus such as SPI, I2C, etc.
  * @fast_io:	  Register IO is fast. Use a spinlock instead of a mutex
  *	     	  to perform locking. This field is ignored if custom lock/unlock
  *	     	  functions are used (see fields lock/unlock of struct regmap_config).

@@ -372,6 +377,8 @@ struct regmap_config {
 
 	int (*reg_read)(void *context, unsigned int reg, unsigned int *val);
 	int (*reg_write)(void *context, unsigned int reg, unsigned int val);
+	int (*reg_update_bits)(void *context, unsigned int reg,
+			       unsigned int mask, unsigned int val);
 
 	bool fast_io;