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Commit 19b6ef51 authored by Tomasz Stanislawski's avatar Tomasz Stanislawski Committed by Mauro Carvalho Chehab
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[media] Documentation: media: description of DMABUF exporting in V4L2 

This patch adds description and usage examples for exporting
DMABUF file descriptor in V4L2.
Signed-off-by: default avatarTomasz Stanislawski <t.stanislaws@samsung.com>
Signed-off-by: default avatarKyungmin Park <kyungmin.park@samsung.com>
Acked-by: default avatarHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@redhat.com>
parent b799d09a
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Documentation/DocBook/media/v4l/compat.xml
View file @ 19b6ef51
......@@ -2590,6 +2590,9 @@ ioctls.</para>
<para>Importing DMABUF file descriptors as a new IO method described
in <xref linkend="dmabuf" />.</para>
</listitem>
<listitem>
<para>Exporting DMABUF files using &VIDIOC-EXPBUF; ioctl.</para>
</listitem>
</itemizedlist>
</section>
......
Documentation/DocBook/media/v4l/io.xml
View file @ 19b6ef51
......@@ -488,6 +488,9 @@ DMA buffer from userspace using a file descriptor previously exported for a
different or the same device (known as the importer role), or both. This
section describes the DMABUF importer role API in V4L2.</para>
<para>Refer to <link linked="vidioc-expbuf"> DMABUF exporting </link> for
details about exporting V4L2 buffers as DMABUF file descriptors.</para>
<para>Input and output devices support the streaming I/O method when the
<constant>V4L2_CAP_STREAMING</constant> flag in the
<structfield>capabilities</structfield> field of &v4l2-capability; returned by
......
Documentation/DocBook/media/v4l/v4l2.xml
View file @ 19b6ef51
......@@ -543,6 +543,7 @@ and discussions on the V4L mailing list.</revremark>
&sub-enuminput;
&sub-enumoutput;
&sub-enumstd;
&sub-expbuf;
&sub-g-audio;
&sub-g-audioout;
&sub-g-crop;
......
Documentation/DocBook/media/v4l/vidioc-expbuf.xml 0 → 100644
View file @ 19b6ef51
<refentry id="vidioc-expbuf">
<refmeta>
<refentrytitle>ioctl VIDIOC_EXPBUF</refentrytitle>
&manvol;
</refmeta>
<refnamediv>
<refname>VIDIOC_EXPBUF</refname>
<refpurpose>Export a buffer as a DMABUF file descriptor.</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 v4l2_exportbuffer *<parameter>argp</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Arguments</title>
<variablelist>
<varlistentry>
<term><parameter>fd</parameter></term>
<listitem>
<para>&fd;</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>request</parameter></term>
<listitem>
<para>VIDIOC_EXPBUF</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>argp</parameter></term>
<listitem>
<para></para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Description</title>
<note>
<title>Experimental</title>
<para>This is an <link linkend="experimental"> experimental </link>
interface and may change in the future.</para>
</note>
<para>This ioctl is an extension to the <link linkend="mmap">memory
mapping</link> I/O method, therefore it is available only for
<constant>V4L2_MEMORY_MMAP</constant> buffers. It can be used to export a
buffer as a DMABUF file at any time after buffers have been allocated with the
&VIDIOC-REQBUFS; ioctl.</para>
<para> To export a buffer, applications fill &v4l2-exportbuffer;. The
<structfield> type </structfield> field is set to the same buffer type as was
previously used with &v4l2-requestbuffers;<structfield> type </structfield>.
Applications must also set the <structfield> index </structfield> field. Valid
index numbers range from zero to the number of buffers allocated with
&VIDIOC-REQBUFS; (&v4l2-requestbuffers;<structfield> count </structfield>)
minus one. For the multi-planar API, applications set the <structfield> plane
</structfield> field to the index of the plane to be exported. Valid planes
range from zero to the maximal number of valid planes for the currently active
format. For the single-planar API, applications must set <structfield> plane
</structfield> to zero. Additional flags may be posted in the <structfield>
flags </structfield> field. Refer to a manual for open() for details.
Currently only O_CLOEXEC is supported. All other fields must be set to zero.
In the case of multi-planar API, every plane is exported separately using
multiple <constant> VIDIOC_EXPBUF </constant> calls. </para>
<para> After calling <constant>VIDIOC_EXPBUF</constant> the <structfield> fd
</structfield> field will be set by a driver. This is a DMABUF file
descriptor. The application may pass it to other DMABUF-aware devices. Refer to
<link linkend="dmabuf">DMABUF importing</link> for details about importing
DMABUF files into V4L2 nodes. It is recommended to close a DMABUF file when it
is no longer used to allow the associated memory to be reclaimed. </para>
</refsect1>
<refsect1>
<section>
<title>Examples</title>
<example>
<title>Exporting a buffer.</title>
<programlisting>
int buffer_export(int v4lfd, &v4l2-buf-type; bt, int index, int *dmafd)
{
&v4l2-exportbuffer; expbuf;
memset(&amp;expbuf, 0, sizeof(expbuf));
expbuf.type = bt;
expbuf.index = index;
if (ioctl(v4lfd, &VIDIOC-EXPBUF;, &amp;expbuf) == -1) {
perror("VIDIOC_EXPBUF");
return -1;
}
*dmafd = expbuf.fd;
return 0;
}
</programlisting>
</example>
<example>
<title>Exporting a buffer using the multi-planar API.</title>
<programlisting>
int buffer_export_mp(int v4lfd, &v4l2-buf-type; bt, int index,
int dmafd[], int n_planes)
{
int i;
for (i = 0; i &lt; n_planes; ++i) {
&v4l2-exportbuffer; expbuf;
memset(&amp;expbuf, 0, sizeof(expbuf));
expbuf.type = bt;
expbuf.index = index;
expbuf.plane = i;
if (ioctl(v4lfd, &VIDIOC-EXPBUF;, &amp;expbuf) == -1) {
perror("VIDIOC_EXPBUF");
while (i)
close(dmafd[--i]);
return -1;
}
dmafd[i] = expbuf.fd;
}
return 0;
}
</programlisting>
</example>
</section>
</refsect1>
<refsect1>
<table pgwide="1" frame="none" id="v4l2-exportbuffer">
<title>struct <structname>v4l2_exportbuffer</structname></title>
<tgroup cols="3">
&cs-str;
<tbody valign="top">
<row>
<entry>__u32</entry>
<entry><structfield>type</structfield></entry>
<entry>Type of the buffer, same as &v4l2-format;
<structfield>type</structfield> or &v4l2-requestbuffers;
<structfield>type</structfield>, set by the application. See <xref
linkend="v4l2-buf-type" /></entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>index</structfield></entry>
<entry>Number of the buffer, set by the application. This field is
only used for <link linkend="mmap">memory mapping</link> I/O and can range from
zero to the number of buffers allocated with the &VIDIOC-REQBUFS; and/or
&VIDIOC-CREATE-BUFS; ioctls. </entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>plane</structfield></entry>
<entry>Index of the plane to be exported when using the
multi-planar API. Otherwise this value must be set to zero. </entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>flags</structfield></entry>
<entry>Flags for the newly created file, currently only <constant>
O_CLOEXEC </constant> is supported, refer to the manual of open() for more
details.</entry>
</row>
<row>
<entry>__s32</entry>
<entry><structfield>fd</structfield></entry>
<entry>The DMABUF file descriptor associated with a buffer. Set by
the driver.</entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>reserved[11]</structfield></entry>
<entry>Reserved field for future use. Must be set to zero.</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1>
&return-value;
<variablelist>
<varlistentry>
<term><errorcode>EINVAL</errorcode></term>
<listitem>
<para>A queue is not in MMAP mode or DMABUF exporting is not
supported or <structfield> flags </structfield> or <structfield> type
</structfield> or <structfield> index </structfield> or <structfield> plane
</structfield> fields are invalid.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
</refentry>
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