DocBook: media: Document ALPHA_COMPONENT control usage on output devices

Extend the V4L2_CID_ALPHA_COMPONENT control for use on output devices,
to set the alpha component value when the output format doesn't have an
alpha channel.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
(cherry picked from commit e632d2f4e25c574a29b269f9f4b0cef2995e402d)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

diff --git a/Documentation/DocBook/media/v4l/controls.xml b/Documentation/DocBook/media/v4l/controls.xml
index a5a3188..066800d 100644 (file)
--- a/Documentation/DocBook/media/v4l/controls.xml
+++ b/Documentation/DocBook/media/v4l/controls.xml
@@ -398,14 +398,17 @@ to work.</entry>
          <row id="v4l2-alpha-component">
            <entry><constant>V4L2_CID_ALPHA_COMPONENT</constant></entry>
            <entry>integer</entry>
-           <entry> Sets the alpha color component on the capture device or on
-           the capture buffer queue of a mem-to-mem device. When a mem-to-mem
-           device produces frame format that includes an alpha component
+           <entry>Sets the alpha color component. When a capture device (or
+           capture queue of a mem-to-mem device) produces a frame format that
+           includes an alpha component
            (e.g. <link linkend="rgb-formats">packed RGB image formats</link>)
-           and the alpha value is not defined by the mem-to-mem input data
-           this control lets you select the alpha component value of all
-           pixels. It is applicable to any pixel format that contains an alpha
-           component.
+           and the alpha value is not defined by the device or the mem-to-mem
+           input data this control lets you select the alpha component value of
+           all pixels. When an output device (or output queue of a mem-to-mem
+           device) consumes a frame format that doesn't include an alpha
+           component and the device supports alpha channel processing this
+           control lets you set the alpha component value of all pixels for
+           further processing in the device.
            </entry>
          </row>
          <row>