regmap: new API regmap_multi_reg_write() definition

New API regmap_multi_reg_write() is defined that allows a set of reg,val
pairs to be written to a I2C client device as one block transfer from the
point of view of a single I2C master system.

A simple demonstration implementation is included that just splits the
block write request into a sequence of single register writes.

The implementation will be modified later to support those I2C clients
that implement the alternative non-standard MULTIWRITE block write mode
so to achieve a single I2C transfer that will be atomic even in multiple
I2C master systems.

Signed-off-by: Anthony Olech <anthony.olech.opensource@diasemi.com>
Signed-off-by: David Dajun Chen <david.chen@diasemi.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

drivers/base/regmap/regmap.c

@@ -1439,6 +1439,47 @@ int regmap_bulk_write(struct regmap *map, unsigned int reg, const void *val,
 }
 EXPORT_SYMBOL_GPL(regmap_bulk_write);
 
+/*
+ * regmap_multi_reg_write(): Write multiple registers to the device
+ *
+ * where the set of register are supplied in any order
+ *
+ * @map: Register map to write to
+ * @regs: Array of structures containing register,value to be written
+ * @num_regs: Number of registers to write
+ *
+ * This function is intended to be used for writing a large block of data
+ * atomically to the device in single transfer for those I2C client devices
+ * that implement this alternative block write mode.
+ *
+ * A value of zero will be returned on success, a negative errno will
+ * be returned in error cases.
+ */
+int regmap_multi_reg_write(struct regmap *map, struct reg_default *regs,
+				int num_regs)
+{
+	int ret = 0, i;
+
+	for (i = 0; i < num_regs; i++) {
+		int reg = regs[i].reg;
+		if (reg % map->reg_stride)
+			return -EINVAL;
+	}
+
+	map->lock(map->lock_arg);
+
+	for (i = 0; i < num_regs; i++) {
+		ret = _regmap_write(map, regs[i].reg, regs[i].def);
+		if (ret != 0)
+			goto out;
+	}
+out:
+	map->unlock(map->lock_arg);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(regmap_multi_reg_write);
+
 /**
  * regmap_raw_write_async(): Write raw values to one or more registers
  *                           asynchronously

include/linux/regmap.h

@@ -378,6 +378,8 @@ int regmap_raw_write(struct regmap *map, unsigned int reg,
 		     const void *val, size_t val_len);
 int regmap_bulk_write(struct regmap *map, unsigned int reg, const void *val,
 			size_t val_count);
+int regmap_multi_reg_write(struct regmap *map, struct reg_default *regs,
+			int num_regs);
 int regmap_raw_write_async(struct regmap *map, unsigned int reg,
 			   const void *val, size_t val_len);
 int regmap_read(struct regmap *map, unsigned int reg, unsigned int *val);