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[media] DocBook media: update three sections of common.xml 

Updates for the "Tuners and Modulators", "Video Standards" and
"Digital Video (DV) Timings" sections.

Besides lots of trivial little fixes the main changes are:

- Remove two footnotes from "Video Standards": the first is a discussion
  of alternative methods of setting standards, which is pretty pointless
  since the standards API is effectively frozen anyway, and the second
  points to 'rationale' that makes little or no sense to me.

- Clarify a few things in the "Digital Video (DV) Timings" section.
  It was awkwardly formatted as well: there used to be a list with
  multiple bullets that has been reduced to a single item, so drop the
  list and rewrite that text.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
This commit is contained in:
Hans Verkuil 2014-01-07 09:39:57 -03:00 committed by Mauro Carvalho Chehab
parent 1c656c87ac
commit d4d6819f9b
1 changed files with 53 additions and 79 deletions
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132
Documentation/DocBook/media/v4l/common.xml
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@ -449,7 +449,7 @@ the tuner.</para>
video inputs.</para>
<para>To query and change tuner properties applications use the
&VIDIOC-G-TUNER; and &VIDIOC-S-TUNER; ioctl, respectively. The
&VIDIOC-G-TUNER; and &VIDIOC-S-TUNER; ioctls, respectively. The
&v4l2-tuner; returned by <constant>VIDIOC_G_TUNER</constant> also
contains signal status information applicable when the tuner of the
current video or radio input is queried. Note that
@ -514,7 +514,7 @@ standards or variations of standards. Each video input and output may
support another set of standards. This set is reported by the
<structfield>std</structfield> field of &v4l2-input; and
&v4l2-output; returned by the &VIDIOC-ENUMINPUT; and
&VIDIOC-ENUMOUTPUT; ioctl, respectively.</para>
&VIDIOC-ENUMOUTPUT; ioctls, respectively.</para>
<para>V4L2 defines one bit for each analog video standard
currently in use worldwide, and sets aside bits for driver defined
@ -545,28 +545,10 @@ 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 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
&v4l2-output; <structfield>std</structfield> field would be a set of
indices like <structfield>audioset</structfield>.</para>
<para>Indices are consistent with the rest of the API
and identify the standard unambiguously. In the present scheme of
things an enumerated standard is looked up by &v4l2-std-id;. Now the
standards supported by the inputs of a device can overlap. Just
assume the tuner and composite input in the example above both
exist on a device. An enumeration of "PAL-B/G", "PAL-H/I" suggests
a choice which does not exist. We cannot merge or omit sets, because
applications would be unable to find the standards reported by
<constant>VIDIOC_G_STD</constant>. That leaves separate enumerations
for each input. Also selecting a standard by &v4l2-std-id; can be
ambiguous. Advantage of this method is that applications need not
identify the standard indirectly, after enumerating.</para><para>So in
summary, the lookup itself is unavoidable. The difference is only
whether the lookup is necessary to find an enumerated standard or to
switch to a standard by &v4l2-std-id;.</para>
</footnote> Drivers must implement all video standard ioctls
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. Drivers must implement all video standard ioctls
when the device has one or more video inputs or outputs.</para>
<para>Special rules apply to devices such as USB cameras where the notion of video
@ -585,17 +567,10 @@ 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
&ENOTTY;.<footnote>
<para>See <xref linkend="buffer" /> for a rationale.</para>
&ENOTTY; or the &EINVAL;.</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>
<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
up to normal expectations, instead of this exception.</para>
</footnote></para>
can be used with the given input or output.</para>
<example>
<title>Information about the current video standard</title>
@ -604,22 +579,22 @@ up to normal expectations, instead of this exception.</para>
&v4l2-std-id; std_id;
&v4l2-standard; standard;
if (-1 == ioctl (fd, &VIDIOC-G-STD;, &amp;std_id)) {
if (-1 == ioctl(fd, &VIDIOC-G-STD;, &amp;std_id)) {
/* Note when VIDIOC_ENUMSTD always returns ENOTTY this
is no video device or it falls under the USB exception,
and VIDIOC_G_STD returning ENOTTY is no error. */
perror ("VIDIOC_G_STD");
exit (EXIT_FAILURE);
perror("VIDIOC_G_STD");
exit(EXIT_FAILURE);
}
memset (&amp;standard, 0, sizeof (standard));
memset(&amp;standard, 0, sizeof(standard));
standard.index = 0;
while (0 == ioctl (fd, &VIDIOC-ENUMSTD;, &amp;standard)) {
while (0 == ioctl(fd, &VIDIOC-ENUMSTD;, &amp;standard)) {
if (standard.id &amp; std_id) {
printf ("Current video standard: %s\n", standard.name);
exit (EXIT_SUCCESS);
printf("Current video standard: %s\n", standard.name);
exit(EXIT_SUCCESS);
}
standard.index++;
@ -629,8 +604,8 @@ while (0 == ioctl (fd, &VIDIOC-ENUMSTD;, &amp;standard)) {
empty unless this device falls under the USB exception. */
if (errno == EINVAL || standard.index == 0) {
perror ("VIDIOC_ENUMSTD");
exit (EXIT_FAILURE);
perror("VIDIOC_ENUMSTD");
exit(EXIT_FAILURE);
}
</programlisting>
</example>
@ -643,26 +618,26 @@ input</title>
&v4l2-input; input;
&v4l2-standard; standard;
memset (&amp;input, 0, sizeof (input));
memset(&amp;input, 0, sizeof(input));
if (-1 == ioctl (fd, &VIDIOC-G-INPUT;, &amp;input.index)) {
perror ("VIDIOC_G_INPUT");
exit (EXIT_FAILURE);
if (-1 == ioctl(fd, &VIDIOC-G-INPUT;, &amp;input.index)) {
perror("VIDIOC_G_INPUT");
exit(EXIT_FAILURE);
}
if (-1 == ioctl (fd, &VIDIOC-ENUMINPUT;, &amp;input)) {
perror ("VIDIOC_ENUM_INPUT");
exit (EXIT_FAILURE);
if (-1 == ioctl(fd, &VIDIOC-ENUMINPUT;, &amp;input)) {
perror("VIDIOC_ENUM_INPUT");
exit(EXIT_FAILURE);
}
printf ("Current input %s supports:\n", input.name);
printf("Current input %s supports:\n", input.name);
memset (&amp;standard, 0, sizeof (standard));
memset(&amp;standard, 0, sizeof(standard));
standard.index = 0;
while (0 == ioctl (fd, &VIDIOC-ENUMSTD;, &amp;standard)) {
while (0 == ioctl(fd, &VIDIOC-ENUMSTD;, &amp;standard)) {
if (standard.id &amp; input.std)
printf ("%s\n", standard.name);
printf("%s\n", standard.name);
standard.index++;
}
@ -671,8 +646,8 @@ while (0 == ioctl (fd, &VIDIOC-ENUMSTD;, &amp;standard)) {
empty unless this device falls under the USB exception. */
if (errno != EINVAL || standard.index == 0) {
perror ("VIDIOC_ENUMSTD");
exit (EXIT_FAILURE);
perror("VIDIOC_ENUMSTD");
exit(EXIT_FAILURE);
}
</programlisting>
</example>
@ -684,21 +659,21 @@ if (errno != EINVAL || standard.index == 0) {
&v4l2-input; input;
&v4l2-std-id; std_id;
memset (&amp;input, 0, sizeof (input));
memset(&amp;input, 0, sizeof(input));
if (-1 == ioctl (fd, &VIDIOC-G-INPUT;, &amp;input.index)) {
perror ("VIDIOC_G_INPUT");
exit (EXIT_FAILURE);
if (-1 == ioctl(fd, &VIDIOC-G-INPUT;, &amp;input.index)) {
perror("VIDIOC_G_INPUT");
exit(EXIT_FAILURE);
}
if (-1 == ioctl (fd, &VIDIOC-ENUMINPUT;, &amp;input)) {
perror ("VIDIOC_ENUM_INPUT");
exit (EXIT_FAILURE);
if (-1 == ioctl(fd, &VIDIOC-ENUMINPUT;, &amp;input)) {
perror("VIDIOC_ENUM_INPUT");
exit(EXIT_FAILURE);
}
if (0 == (input.std &amp; V4L2_STD_PAL_BG)) {
fprintf (stderr, "Oops. B/G PAL is not supported.\n");
exit (EXIT_FAILURE);
fprintf(stderr, "Oops. B/G PAL is not supported.\n");
exit(EXIT_FAILURE);
}
/* Note this is also supposed to work when only B
@ -706,9 +681,9 @@ if (0 == (input.std &amp; V4L2_STD_PAL_BG)) {
std_id = V4L2_STD_PAL_BG;
if (-1 == ioctl (fd, &VIDIOC-S-STD;, &amp;std_id)) {
perror ("VIDIOC_S_STD");
exit (EXIT_FAILURE);
if (-1 == ioctl(fd, &VIDIOC-S-STD;, &amp;std_id)) {
perror("VIDIOC_S_STD");
exit(EXIT_FAILURE);
}
</programlisting>
</example>
@ -721,26 +696,25 @@ corresponding video timings. Today there are many more different hardware interf
such as High Definition TV interfaces (HDMI), VGA, DVI connectors etc., that carry
video signals and there is a need to extend the API to select the video timings
for these interfaces. Since it is not possible to extend the &v4l2-std-id; due to
the limited bits available, a new set of IOCTLs was added to set/get video timings at
the input and output: </para><itemizedlist>
<listitem>
<para>DV Timings: This will allow applications to define detailed
video timings for the interface. This includes parameters such as width, height,
polarities, frontporch, backporch etc. The <filename>linux/v4l2-dv-timings.h</filename>
the limited bits available, a new set of ioctls was added to set/get video timings at
the input and output.</para>
<para>These ioctls deal with the detailed digital video timings that define
each video format. This includes parameters such as the active video width and height,
signal polarities, frontporches, backporches, sync widths etc. The <filename>linux/v4l2-dv-timings.h</filename>
header can be used to get the timings of the formats in the <xref linkend="cea861" /> and
<xref linkend="vesadmt" /> standards.
</para>
</listitem>
</itemizedlist>
<para>To enumerate and query the attributes of the DV timings supported by a device,
<para>To enumerate and query the attributes of the DV timings supported by a device
applications use the &VIDIOC-ENUM-DV-TIMINGS; and &VIDIOC-DV-TIMINGS-CAP; ioctls.
To set DV timings for the device, applications use the
To set DV timings for the device applications use the
&VIDIOC-S-DV-TIMINGS; ioctl and to get current DV timings they use the
&VIDIOC-G-DV-TIMINGS; ioctl. To detect the DV timings as seen by the video receiver applications
use the &VIDIOC-QUERY-DV-TIMINGS; ioctl.</para>
<para>Applications can make use of the <xref linkend="input-capabilities" /> and
<xref linkend="output-capabilities"/> flags to decide what ioctls are available to set the
video timings for the device.</para>
<xref linkend="output-capabilities"/> flags to determine whether the digital video ioctls
can be used with the given input or output.</para>
</section>
&sub-controls;