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-rw-r--r--Documentation/DocBook/media/v4l/common.xml30
1 files changed, 14 insertions, 16 deletions
diff --git a/Documentation/DocBook/media/v4l/common.xml b/Documentation/DocBook/media/v4l/common.xml
index b91d25313b63..73c6847436c9 100644
--- a/Documentation/DocBook/media/v4l/common.xml
+++ b/Documentation/DocBook/media/v4l/common.xml
@@ -564,7 +564,7 @@ automatically.</para>
564 <para>To query and select the standard used by the current video 564 <para>To query and select the standard used by the current video
565input or output applications call the &VIDIOC-G-STD; and 565input or output applications call the &VIDIOC-G-STD; and
566&VIDIOC-S-STD; ioctl, respectively. The <emphasis>received</emphasis> 566&VIDIOC-S-STD; ioctl, respectively. The <emphasis>received</emphasis>
567standard 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> 567standard 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>
568 <para>An alternative to the current scheme is to use pointers 568 <para>An alternative to the current scheme is to use pointers
569to indices as arguments of <constant>VIDIOC_G_STD</constant> and 569to indices as arguments of <constant>VIDIOC_G_STD</constant> and
570<constant>VIDIOC_S_STD</constant>, the &v4l2-input; and 570<constant>VIDIOC_S_STD</constant>, the &v4l2-input; and
@@ -588,30 +588,28 @@ switch to a standard by &v4l2-std-id;.</para>
588 </footnote> Drivers must implement all video standard ioctls 588 </footnote> Drivers must implement all video standard ioctls
589when the device has one or more video inputs or outputs.</para> 589when the device has one or more video inputs or outputs.</para>
590 590
591 <para>Special rules apply to USB cameras where the notion of video 591 <para>Special rules apply to devices such as USB cameras where the notion of video
592standards makes little sense. More generally any capture device, 592standards makes little sense. More generally for any capture or output device
593output devices accordingly, which is <itemizedlist> 593which is: <itemizedlist>
594 <listitem> 594 <listitem>
595 <para>incapable of capturing fields or frames at the nominal 595 <para>incapable of capturing fields or frames at the nominal
596rate of the video standard, or</para> 596rate of the video standard, or</para>
597 </listitem> 597 </listitem>
598 <listitem> 598 <listitem>
599 <para>where <link linkend="buffer">timestamps</link> refer 599 <para>that does not support the video standard formats at all.</para>
600to the instant the field or frame was received by the driver, not the
601capture time, or</para>
602 </listitem>
603 <listitem>
604 <para>where <link linkend="buffer">sequence numbers</link>
605refer to the frames received by the driver, not the captured
606frames.</para>
607 </listitem> 600 </listitem>
608 </itemizedlist> Here the driver shall set the 601 </itemizedlist> Here the driver shall set the
609<structfield>std</structfield> field of &v4l2-input; and &v4l2-output; 602<structfield>std</structfield> field of &v4l2-input; and &v4l2-output;
610to zero, the <constant>VIDIOC_G_STD</constant>, 603to zero and the <constant>VIDIOC_G_STD</constant>,
611<constant>VIDIOC_S_STD</constant>, 604<constant>VIDIOC_S_STD</constant>,
612<constant>VIDIOC_QUERYSTD</constant> and 605<constant>VIDIOC_QUERYSTD</constant> and
613<constant>VIDIOC_ENUMSTD</constant> ioctls shall return the 606<constant>VIDIOC_ENUMSTD</constant> ioctls shall return the
614&EINVAL;.<footnote> 607&ENOTTY;.<footnote>
608 <para>See <xref linkend="buffer" /> for a rationale.</para>
609 <para>Applications can make use of the <xref linkend="input-capabilities" /> and
610<xref linkend="output-capabilities"/> flags to determine whether the video standard ioctls
611are available for the device.</para>
612&ENOTTY;.
615 <para>See <xref linkend="buffer" /> for a rationale. Probably 613 <para>See <xref linkend="buffer" /> for a rationale. Probably
616even USB cameras follow some well known video standard. It might have 614even USB cameras follow some well known video standard. It might have
617been better to explicitly indicate elsewhere if a device cannot live 615been better to explicitly indicate elsewhere if a device cannot live
@@ -626,9 +624,9 @@ up to normal expectations, instead of this exception.</para>
626&v4l2-standard; standard; 624&v4l2-standard; standard;
627 625
628if (-1 == ioctl (fd, &VIDIOC-G-STD;, &amp;std_id)) { 626if (-1 == ioctl (fd, &VIDIOC-G-STD;, &amp;std_id)) {
629 /* Note when VIDIOC_ENUMSTD always returns EINVAL this 627 /* Note when VIDIOC_ENUMSTD always returns ENOTTY this
630 is no video device or it falls under the USB exception, 628 is no video device or it falls under the USB exception,
631 and VIDIOC_G_STD returning EINVAL is no error. */ 629 and VIDIOC_G_STD returning ENOTTY is no error. */
632 630
633 perror ("VIDIOC_G_STD"); 631 perror ("VIDIOC_G_STD");
634 exit (EXIT_FAILURE); 632 exit (EXIT_FAILURE);