linux/Documentation/DocBook/v4l/media-ioc-setup-link.xml
Laurent Pinchart e02188c90f [media] media: Pipelines and media streams
Drivers often need to associate pipeline objects to entities, and to
take stream state into account when configuring entities and links. The
pipeline API helps drivers manage that information.

When starting streaming, drivers call media_entity_pipeline_start(). The
function marks all entities connected to the given entity through
enabled links, either directly or indirectly, as streaming. Similarly,
when stopping the stream, drivers call media_entity_pipeline_stop().

The media_entity_pipeline_start() function takes a pointer to a media
pipeline and stores it in every entity in the graph. Drivers should
embed the media_pipeline structure in higher-level pipeline structures
and can then access the pipeline through the media_entity structure.

Link configuration will fail with -EBUSY by default if either end of the
link is a streaming entity, unless the link is marked with the
MEDIA_LNK_FL_DYNAMIC flag.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
2011-03-22 04:53:17 -03:00

93 lines
3 KiB
XML

<refentry id="media-ioc-setup-link">
<refmeta>
<refentrytitle>ioctl MEDIA_IOC_SETUP_LINK</refentrytitle>
&manvol;
</refmeta>
<refnamediv>
<refname>MEDIA_IOC_SETUP_LINK</refname>
<refpurpose>Modify the properties of a link</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcprototype>
<funcdef>int <function>ioctl</function></funcdef>
<paramdef>int <parameter>fd</parameter></paramdef>
<paramdef>int <parameter>request</parameter></paramdef>
<paramdef>struct media_link_desc *<parameter>argp</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Arguments</title>
<variablelist>
<varlistentry>
<term><parameter>fd</parameter></term>
<listitem>
<para>File descriptor returned by
<link linkend='media-func-open'><function>open()</function></link>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>request</parameter></term>
<listitem>
<para>MEDIA_IOC_ENUM_LINKS</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>argp</parameter></term>
<listitem>
<para></para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Description</title>
<para>To change link properties applications fill a &media-link-desc; with
link identification information (source and sink pad) and the new requested
link flags. They then call the MEDIA_IOC_SETUP_LINK ioctl with a pointer to
that structure.</para>
<para>The only configurable property is the <constant>ENABLED</constant>
link flag to enable/disable a link. Links marked with the
<constant>IMMUTABLE</constant> link flag can not be enabled or disabled.
</para>
<para>Link configuration has no side effect on other links. If an enabled
link at the sink pad prevents the link from being enabled, the driver
returns with an &EBUSY;.</para>
<para>Only links marked with the <constant>DYNAMIC</constant> link flag can
be enabled/disabled while streaming media data. Attempting to enable or
disable a streaming non-dynamic link will return an &EBUSY;.</para>
<para>If the specified link can't be found the driver returns with an
&EINVAL;.</para>
</refsect1>
<refsect1>
&return-value;
<variablelist>
<varlistentry>
<term><errorcode>EBUSY</errorcode></term>
<listitem>
<para>The link properties can't be changed because the link is
currently busy. This can be caused, for instance, by an active media
stream (audio or video) on the link. The ioctl shouldn't be retried if
no other action is performed before to fix the problem.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><errorcode>EINVAL</errorcode></term>
<listitem>
<para>The &media-link-desc; references a non-existing link, or the
link is immutable and an attempt to modify its configuration was made.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
</refentry>