[media] tuner-core/v4l2-subdev: document that the type field has to be filled in

The tuner ops g_frequency, g_tuner and s_tuner require that the tuner type
field is filled in. Document this.

The tuner-core doc is based on a patch from Mauro Carvalho Chehab <mchehab@redhat.com>.
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/tuner-core.c

@@ -1117,6 +1117,16 @@ static int tuner_s_frequency(struct v4l2_subdev *sd, struct v4l2_frequency *f)
 	return 0;
 }
 
+/**
+ * tuner_g_frequency - Get the tuned frequency for the tuner
+ * @sd: pointer to struct v4l2_subdev
+ * @f: pointer to struct v4l2_frequency
+ *
+ * At return, the structure f will be filled with tuner frequency
+ * if the tuner matches the f->type.
+ * Note: f->type should be initialized before calling it.
+ * This is done by either video_ioctl2 or by the bridge driver.
+ */
 static int tuner_g_frequency(struct v4l2_subdev *sd, struct v4l2_frequency *f)
 {
 	struct tuner *t = to_tuner(sd);
@@ -1139,6 +1149,16 @@ static int tuner_g_frequency(struct v4l2_subdev *sd, struct v4l2_frequency *f)
 	return 0;
 }
 
+/**
+ * tuner_g_tuner - Fill in tuner information
+ * @sd: pointer to struct v4l2_subdev
+ * @vt: pointer to struct v4l2_tuner
+ *
+ * At return, the structure vt will be filled with tuner information
+ * if the tuner matches vt->type.
+ * Note: vt->type should be initialized before calling it.
+ * This is done by either video_ioctl2 or by the bridge driver.
+ */
 static int tuner_g_tuner(struct v4l2_subdev *sd, struct v4l2_tuner *vt)
 {
 	struct tuner *t = to_tuner(sd);
@@ -1179,6 +1199,15 @@ static int tuner_g_tuner(struct v4l2_subdev *sd, struct v4l2_tuner *vt)
 	return 0;
 }
 
+/**
+ * tuner_s_tuner - Set the tuner's audio mode
+ * @sd: pointer to struct v4l2_subdev
+ * @vt: pointer to struct v4l2_tuner
+ *
+ * Sets the audio mode if the tuner matches vt->type.
+ * Note: vt->type should be initialized before calling it.
+ * This is done by either video_ioctl2 or by the bridge driver.
+ */
 static int tuner_s_tuner(struct v4l2_subdev *sd, struct v4l2_tuner *vt)
 {
 	struct tuner *t = to_tuner(sd);

include/media/v4l2-subdev.h

@@ -175,6 +175,13 @@ struct v4l2_subdev_core_ops {
 
 /* s_radio: v4l device was opened in radio mode.
 
+   g_frequency: freq->type must be filled in. Normally done by video_ioctl2
+	or the bridge driver.
+
+   g_tuner:
+   s_tuner: vt->type must be filled in. Normally done by video_ioctl2 or the
+	bridge driver.
+
    s_type_addr: sets tuner type and its I2C addr.
 
    s_config: sets tda9887 specific stuff, like port1, port2 and qss