dm: i2c: Add a function to transfer messages

Sometimes it is useful to be able to transfer a raw I2C message. This
happens when the chip address needs to be set manually, or when the data to
be sent/received is in another buffer.

Add a function to provide access to this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Heiko Schocher <hs@denx.de>

drivers/i2c/i2c-uclass.c

@@ -202,6 +202,17 @@ int dm_i2c_write(struct udevice *dev, uint offset, const uint8_t *buffer,
 	}
 }
 
+int dm_i2c_xfer(struct udevice *dev, struct i2c_msg *msg, int nmsgs)
+{
+	struct udevice *bus = dev_get_parent(dev);
+	struct dm_i2c_ops *ops = i2c_get_ops(bus);
+
+	if (!ops->xfer)
+		return -ENOSYS;
+
+	return ops->xfer(bus, msg, nmsgs);
+}
+
 int dm_i2c_reg_read(struct udevice *dev, uint offset)
 {
 	uint8_t val;

include/i2c.h

@@ -191,6 +191,19 @@ int dm_i2c_reg_read(struct udevice *dev, uint offset);
 int dm_i2c_reg_write(struct udevice *dev, uint offset, unsigned int val);
 
 /**
+ * dm_i2c_xfer() - Transfer messages over I2C
+ *
+ * This transfers a raw message. It is best to use dm_i2c_reg_read/write()
+ * instead.
+ *
+ * @dev:	Device to use for transfer
+ * @msg:	List of messages to transfer
+ * @nmsgs:	Number of messages to transfer
+ * @return 0 on success, -ve on error
+ */
+int dm_i2c_xfer(struct udevice *dev, struct i2c_msg *msg, int nmsgs);
+
+/**
  * dm_i2c_set_bus_speed() - set the speed of a bus
  *
  * @bus:	Bus to adjust