Add a mechanism for sending multi-part messages to the I2C driver base class.

apps/drivers/device/i2c.cpp

@@ -166,4 +166,24 @@ I2C::transfer(const uint8_t *send, unsigned send_len, uint8_t *recv, unsigned re
 
 }
 
+int
+I2C::transfer(i2c_msg_s *msgv, unsigned msgs)
+{
+	for (unsigned i = 0; i < msgs; i++)
+		msgv[i].addr = _address;
+
+	/*
+	 * I2C architecture means there is an unavoidable race here
+	 * if there are any devices on the bus with a different frequency
+	 * preference.  Really, this is pointless.
+	 */
+	I2C_SETFREQUENCY(_dev, _frequency);
+	ret = I2C_TRANSFER(_dev, msgv, msgs);
+
+	if (ret != OK)
+		up_i2creset(_dev);
+
+	return ret;
+}
+
 } // namespace device

apps/drivers/device/i2c.h

@@ -100,6 +100,16 @@ protected:
 	int		transfer(const uint8_t *send, unsigned send_len,
 				 uint8_t *recv, unsigned recv_len);
 
+	/**
+	 * Perform a multi-part I2C transaction to the device.
+	 *
+	 * @param msgv		An I2C message vector.
+	 * @param msgs		The number of entries in the message vector.
+	 * @return		OK if the transfer was successful, -errno
+	 *			otherwise.
+	 */
+	int		transfer(i2c_msg_s *msgv, unsigned msgs);
+
 	/**
 	 * Change the bus address.
 	 *