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[media] DocBook media: update control section 

Document the support for compound types in controls.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
This commit is contained in:
Hans Verkuil 2014-05-05 10:16:49 -03:00 committed by Mauro Carvalho Chehab
parent 48e393a263
commit 680a513968
1 changed files with 20 additions and 7 deletions
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27
Documentation/DocBook/media/v4l/controls.xml
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@ -660,16 +660,29 @@ supported.</para>
&v4l2-control;, except for the fact that it also allows for 64-bit
values and pointers to be passed.</para>
<para>Since the &v4l2-ext-control; supports pointers it is now
also possible to have controls with compound types such as N-dimensional arrays
and/or structures. You need to specify the <constant>V4L2_CTRL_FLAG_NEXT_COMPOUND</constant>
when enumerating controls to actually be able to see such compound controls.
In other words, these controls with compound types should only be used
programmatically.</para>
<para>Since such compound controls need to expose more information
about themselves than is possible with &VIDIOC-QUERYCTRL; the
&VIDIOC-QUERY-EXT-CTRL; ioctl was added. In particular, this ioctl gives
the dimensions of the N-dimensional array if this control consists of more than
one element.</para>
<para>It is important to realize that due to the flexibility of
controls it is necessary to check whether the control you want to set
actually is supported in the driver and what the valid range of values
is. So use the &VIDIOC-QUERYCTRL; and &VIDIOC-QUERYMENU; ioctls to
check this. Also note that it is possible that some of the menu
indices in a control of type <constant>V4L2_CTRL_TYPE_MENU</constant>
may not be supported (<constant>VIDIOC_QUERYMENU</constant> will
return an error). A good example is the list of supported MPEG audio
bitrates. Some drivers only support one or two bitrates, others
support a wider range.</para>
is. So use the &VIDIOC-QUERYCTRL; (or &VIDIOC-QUERY-EXT-CTRL;) and
&VIDIOC-QUERYMENU; ioctls to check this. Also note that it is possible
that some of the menu indices in a control of type
<constant>V4L2_CTRL_TYPE_MENU</constant> may not be supported
(<constant>VIDIOC_QUERYMENU</constant> will return an error). A good
example is the list of supported MPEG audio bitrates. Some drivers only
support one or two bitrates, others support a wider range.</para>
<para>
All controls use machine endianness.