i2c: Restore i2c_smbus_process_call function

Restore the i2c_smbus_process_call() as one driver (for the
Micronas MAP5401) will need it soon.

[JD: Update documentation accordingly.]
Signed-off-by: Prakash Mortha <pmortha@escient.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

Documentation/i2c/smbus-protocol

@@ -109,8 +109,8 @@ specified through the Comm byte.
 S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] P
 
 
-SMBus Process Call
-==================
+SMBus Process Call:  i2c_smbus_process_call()
+=============================================
 
 This command selects a device register (through the Comm byte), sends
 16 bits of data to it, and reads 16 bits of data in return.

Documentation/i2c/writing-clients

@@ -606,6 +606,8 @@ SMBus communication
   extern s32 i2c_smbus_read_word_data(struct i2c_client * client, u8 command);
   extern s32 i2c_smbus_write_word_data(struct i2c_client * client,
                                        u8 command, u16 value);
+  extern s32 i2c_smbus_process_call(struct i2c_client *client,
+                                    u8 command, u16 value);
   extern s32 i2c_smbus_read_block_data(struct i2c_client * client,
                                        u8 command, u8 *values);
   extern s32 i2c_smbus_write_block_data(struct i2c_client * client,
@@ -621,8 +623,6 @@ These ones were removed from i2c-core because they had no users, but could
 be added back later if needed:
 
   extern s32 i2c_smbus_write_quick(struct i2c_client * client, u8 value);
-  extern s32 i2c_smbus_process_call(struct i2c_client * client,
-                                    u8 command, u16 value);
   extern s32 i2c_smbus_block_process_call(struct i2c_client *client,
                                           u8 command, u8 length,
                                           u8 *values)

drivers/i2c/i2c-core.c

@@ -1687,6 +1687,28 @@ s32 i2c_smbus_write_word_data(struct i2c_client *client, u8 command, u16 value)
 }
 EXPORT_SYMBOL(i2c_smbus_write_word_data);
 
+/**
+ * i2c_smbus_process_call - SMBus "process call" protocol
+ * @client: Handle to slave device
+ * @command: Byte interpreted by slave
+ * @value: 16-bit "word" being written
+ *
+ * This executes the SMBus "process call" protocol, returning negative errno
+ * else a 16-bit unsigned "word" received from the device.
+ */
+s32 i2c_smbus_process_call(struct i2c_client *client, u8 command, u16 value)
+{
+	union i2c_smbus_data data;
+	int status;
+	data.word = value;
+
+	status = i2c_smbus_xfer(client->adapter, client->addr, client->flags,
+				I2C_SMBUS_WRITE, command,
+				I2C_SMBUS_PROC_CALL, &data);
+	return (status < 0) ? status : data.word;
+}
+EXPORT_SYMBOL(i2c_smbus_process_call);
+
 /**
  * i2c_smbus_read_block_data - SMBus "block read" protocol
  * @client: Handle to slave device