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[media] DocBook: fix awkward language and fix the documented return value

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The Video Standard section contains some awkward language. It also wasn't
updated when the error code for unimplemented ioctls changed from EINVAL
to ENOTTY.

[mchehab@redhat.com: remove a misplaced footnote tag]
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Hans Verkuil 2012-09-14 07:39:55 -03:00 committed by Mauro Carvalho Chehab
parent 1ff7ebe23d
commit d7a11e1f18
1 changed files with 14 additions and 16 deletions
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30
Documentation/DocBook/media/v4l/common.xml
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@ -564,7 +564,7 @@ automatically.</para>
<para>To query and select the standard used by the current video
input or output applications call the &VIDIOC-G-STD; and
&VIDIOC-S-STD; ioctl, respectively. The <emphasis>received</emphasis>
standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note parameter of all these ioctls is a pointer to a &v4l2-std-id; type (a standard set), <emphasis>not</emphasis> an index into the standard enumeration.<footnote>
standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note that the parameter of all these ioctls is a pointer to a &v4l2-std-id; type (a standard set), <emphasis>not</emphasis> an index into the standard enumeration.<footnote>
<para>An alternative to the current scheme is to use pointers
to indices as arguments of <constant>VIDIOC_G_STD</constant> and
<constant>VIDIOC_S_STD</constant>, the &v4l2-input; and
@ -588,30 +588,28 @@ switch to a standard by &v4l2-std-id;.</para>
</footnote> Drivers must implement all video standard ioctls
when the device has one or more video inputs or outputs.</para>
<para>Special rules apply to USB cameras where the notion of video
standards makes little sense. More generally any capture device,
output devices accordingly, which is <itemizedlist>
<para>Special rules apply to devices such as USB cameras where the notion of video
standards makes little sense. More generally for any capture or output device
which is: <itemizedlist>
<listitem>
<para>incapable of capturing fields or frames at the nominal
rate of the video standard, or</para>
</listitem>
<listitem>
<para>where <link linkend="buffer">timestamps</link> refer
to the instant the field or frame was received by the driver, not the
capture time, or</para>
</listitem>
<listitem>
<para>where <link linkend="buffer">sequence numbers</link>
refer to the frames received by the driver, not the captured
frames.</para>
<para>that does not support the video standard formats at all.</para>
</listitem>
</itemizedlist> Here the driver shall set the
<structfield>std</structfield> field of &v4l2-input; and &v4l2-output;
to zero, the <constant>VIDIOC_G_STD</constant>,
to zero and the <constant>VIDIOC_G_STD</constant>,
<constant>VIDIOC_S_STD</constant>,
<constant>VIDIOC_QUERYSTD</constant> and
<constant>VIDIOC_ENUMSTD</constant> ioctls shall return the
&EINVAL;.<footnote>
&ENOTTY;.<footnote>
<para>See <xref linkend="buffer" /> for a rationale.</para>
<para>Applications can make use of the <xref linkend="input-capabilities" /> and
<xref linkend="output-capabilities"/> flags to determine whether the video standard ioctls
are available for the device.</para>
&ENOTTY;.
<para>See <xref linkend="buffer" /> for a rationale. Probably
even USB cameras follow some well known video standard. It might have
been better to explicitly indicate elsewhere if a device cannot live
@ -626,9 +624,9 @@ up to normal expectations, instead of this exception.</para>
&v4l2-standard; standard;
if (-1 == ioctl (fd, &VIDIOC-G-STD;, &amp;std_id)) {
/* Note when VIDIOC_ENUMSTD always returns EINVAL this
/* Note when VIDIOC_ENUMSTD always returns ENOTTY this
is no video device or it falls under the USB exception,
and VIDIOC_G_STD returning EINVAL is no error. */
and VIDIOC_G_STD returning ENOTTY is no error. */
perror ("VIDIOC_G_STD");
exit (EXIT_FAILURE);