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-rw-r--r--Documentation/DocBook/media/v4l/vidioc-g-modulator.xml6
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/DocBook/media/v4l/vidioc-g-modulator.xml b/Documentation/DocBook/media/v4l/vidioc-g-modulator.xml
index 80167fc4483d..96e17b344c5d 100644
--- a/Documentation/DocBook/media/v4l/vidioc-g-modulator.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-g-modulator.xml
@@ -78,6 +78,12 @@ different audio modulation if the request cannot be satisfied. However
this is a write-only ioctl, it does not return the actual audio
modulation selected.</para>
+ <para><link linkend="sdr">SDR</link> specific modulator types are
+<constant>V4L2_TUNER_SDR</constant> and <constant>V4L2_TUNER_RF</constant>.
+For SDR devices <structfield>txsubchans</structfield> field must be
+initialized to zero.
+The term 'modulator' means SDR transmitter in this context.</para>
+
<para>To change the radio frequency the &VIDIOC-S-FREQUENCY; ioctl
is available.</para>