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.
Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
---
Documentation/DocBook/media/v4l/common.xml | 30 +++++++++++++---------------
1 file changed, 14 insertions(+), 16 deletions(-)
diff --git a/Documentation/DocBook/media/v4l/common.xml b/Documentation/DocBook/media/v4l/common.xml
index b91d253..08db1cf 100644
--- a/Documentation/DocBook/media/v4l/common.xml
+++ b/Documentation/DocBook/media/v4l/common.xml
@@ -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;.<footnote>
<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;, &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);
--
1.7.10.4
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