This ioctl is supported by the DVB core, but was never
documented.

Add a documentation for it.

Signed-off-by: Mauro Carvalho Chehab <mche...@s-opensource.com>
---
 Documentation/media/uapi/dvb/dmx-get-pes-pids.rst | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/Documentation/media/uapi/dvb/dmx-get-pes-pids.rst 
b/Documentation/media/uapi/dvb/dmx-get-pes-pids.rst
index 20288c11d279..fbdbc12869d1 100644
--- a/Documentation/media/uapi/dvb/dmx-get-pes-pids.rst
+++ b/Documentation/media/uapi/dvb/dmx-get-pes-pids.rst
@@ -25,13 +25,31 @@ Arguments
     File descriptor returned by :c:func:`open() <dvb-dmx-open>`.
 
 ``pids``
-    Undocumented.
+    Array used to store 5 Program IDs.
 
 
 Description
 -----------
 
-.. note:: This ioctl is undocumented. Documentation is welcome.
+This ioctl allows to query a DVB device to return the first PID used
+by audio, video, textext, subtitle and PCR programs on a given service.
+They're stored as:
+
+=======================        ========        
=======================================
+PID  element           position        content
+=======================        ========        
=======================================
+pids[DMX_PES_AUDIO]    0               first audio PID
+pids[DMX_PES_VIDEO]    1               first video PID
+pids[DMX_PES_TELETEXT] 2               first teletext PID
+pids[DMX_PES_SUBTITLE] 3               first subtitle PID
+pids[DMX_PES_PCR]      4               first Program Clock Reference PID
+=======================        ========        
=======================================
+
+
+.. note::
+
+       A value equal to 0xffff means that the PID was not filled by the
+       Kernel.
 
 
 Return Value
-- 
2.13.5

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