[media] media: ov2640: add async probe function

In async probe, there is a case that ov2640 is probed before the
host device which provided 'mclk'.
To support this async probe, we will get 'mclk' at first in the probe(),
if failed it will return -EPROBE_DEFER. That will let ov2640 wait for
the host device probed.
Signed-off-by: Josh Wu <josh.wu@atmel.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/i2c/soc_camera/ov2640.c

@@ -1068,6 +1068,10 @@ static int ov2640_probe(struct i2c_client *client,
 		return -ENOMEM;
 	}
 
+	priv->clk = v4l2_clk_get(&client->dev, "mclk");
+	if (IS_ERR(priv->clk))
+		return -EPROBE_DEFER;
+
 	v4l2_i2c_subdev_init(&priv->subdev, client, &ov2640_subdev_ops);
 	v4l2_ctrl_handler_init(&priv->hdl, 2);
 	v4l2_ctrl_new_std(&priv->hdl, &ov2640_ctrl_ops,
@@ -1075,24 +1079,27 @@ static int ov2640_probe(struct i2c_client *client,
 	v4l2_ctrl_new_std(&priv->hdl, &ov2640_ctrl_ops,
 			V4L2_CID_HFLIP, 0, 1, 1, 0);
 	priv->subdev.ctrl_handler = &priv->hdl;
-	if (priv->hdl.error)
-		return priv->hdl.error;
-
-	priv->clk = v4l2_clk_get(&client->dev, "mclk");
-	if (IS_ERR(priv->clk)) {
-		ret = PTR_ERR(priv->clk);
-		goto eclkget;
+	if (priv->hdl.error) {
+		ret = priv->hdl.error;
+		goto err_clk;
 	}
 
 	ret = ov2640_video_probe(client);
-	if (ret) {
-		v4l2_clk_put(priv->clk);
-eclkget:
-		v4l2_ctrl_handler_free(&priv->hdl);
-	} else {
-		dev_info(&adapter->dev, "OV2640 Probed\n");
-	}
+	if (ret < 0)
+		goto err_videoprobe;
 
+	ret = v4l2_async_register_subdev(&priv->subdev);
+	if (ret < 0)
+		goto err_videoprobe;
+
+	dev_info(&adapter->dev, "OV2640 Probed\n");
+
+	return 0;
+
+err_videoprobe:
+	v4l2_ctrl_handler_free(&priv->hdl);
+err_clk:
+	v4l2_clk_put(priv->clk);
 	return ret;
 }
 
@@ -1100,6 +1107,7 @@ static int ov2640_remove(struct i2c_client *client)
 {
 	struct ov2640_priv       *priv = to_ov2640(client);
 
+	v4l2_async_unregister_subdev(&priv->subdev);
 	v4l2_clk_put(priv->clk);
 	v4l2_device_unregister_subdev(&priv->subdev);
 	v4l2_ctrl_handler_free(&priv->hdl);