i2c: mxs: Fix misuse init_completion

The init_completion() call does reinit not only the variable carrying
the flag that the completion finished, but also initialized the
waitqueue associated with the completion. On the contrary, the
INIT_COMPLETION() call only reinits the flag.

In case there was anything still stuck in the waitqueue, subsequent call
to init_completion() would be able to create possible race condition. This
patch uses the proper function and moves init_completion() into .probe() call
of the driver, to be issued only once.

Note that such scenario is impossible, since two threads can never enter the
mxs_i2c_xfer_msg(), since whole this section is protected by mutex in I2C core.
This by no means allows this issue to exit though.
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>

drivers/i2c/busses/i2c-mxs.c

@@ -316,7 +316,7 @@ static int mxs_i2c_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg,
 	if (msg->len == 0)
 		return -EINVAL;
 
-	init_completion(&i2c->cmd_complete);
+	INIT_COMPLETION(i2c->cmd_complete);
 	i2c->cmd_err = 0;
 
 	ret = mxs_i2c_dma_setup_xfer(adap, msg, flags);
@@ -473,6 +473,8 @@ static int mxs_i2c_probe(struct platform_device *pdev)
 	i2c->dev = dev;
 	i2c->speed = &mxs_i2c_95kHz_config;
 
+	init_completion(&i2c->cmd_complete);
+
 	if (dev->of_node) {
 		err = mxs_i2c_get_ofdata(i2c);
 		if (err)