[media] V4L2: add a device pointer to struct v4l2_subdev

It is often useful to have simple means to get from a subdevice to the
underlying physical device. This patch adds such a pointer to struct
v4l2_subdev and sets it accordingly in the I2C and SPI cases.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/v4l2-core/v4l2-common.c

@@ -237,6 +237,7 @@ void v4l2_i2c_subdev_init(struct v4l2_subdev *sd, struct i2c_client *client,
 	sd->flags |= V4L2_SUBDEV_FL_IS_I2C;
 	/* the owner is the same as the i2c_client's driver owner */
 	sd->owner = client->driver->driver.owner;
+	sd->dev = &client->dev;
 	/* i2c_client and v4l2_subdev point to one another */
 	v4l2_set_subdevdata(sd, client);
 	i2c_set_clientdata(client, sd);
@@ -370,6 +371,7 @@ void v4l2_spi_subdev_init(struct v4l2_subdev *sd, struct spi_device *spi,
 	sd->flags |= V4L2_SUBDEV_FL_IS_SPI;
 	/* the owner is the same as the spi_device's driver owner */
 	sd->owner = spi->dev.driver->owner;
+	sd->dev = &spi->dev;
 	/* spi_device and v4l2_subdev point to one another */
 	v4l2_set_subdevdata(sd, spi);
 	spi_set_drvdata(spi, sd);

include/media/v4l2-subdev.h

@@ -583,6 +583,8 @@ struct v4l2_subdev {
 	void *host_priv;
 	/* subdev device node */
 	struct video_device *devnode;
+	/* pointer to the physical device, if any */
+	struct device *dev;
 };
 
 #define media_entity_to_v4l2_subdev(ent) \