[PATCHv9 17/25] Documentation: media: description of DMABUF exporting in V4L2
Tomasz Stanislawski
t.stanislaws at samsung.com
Tue Oct 2 07:27:28 PDT 2012
This patch adds description and usage examples for exporting
DMABUF file descriptor in V4L2.
Signed-off-by: Tomasz Stanislawski <t.stanislaws at samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park at samsung.com>
CC: linux-doc at vger.kernel.org
---
Documentation/DocBook/media/v4l/compat.xml | 3 +
Documentation/DocBook/media/v4l/io.xml | 3 +
Documentation/DocBook/media/v4l/v4l2.xml | 1 +
Documentation/DocBook/media/v4l/vidioc-expbuf.xml | 212 +++++++++++++++++++++
4 files changed, 219 insertions(+)
create mode 100644 Documentation/DocBook/media/v4l/vidioc-expbuf.xml
diff --git a/Documentation/DocBook/media/v4l/compat.xml b/Documentation/DocBook/media/v4l/compat.xml
index a46f95b..f0512aa 100644
--- a/Documentation/DocBook/media/v4l/compat.xml
+++ b/Documentation/DocBook/media/v4l/compat.xml
@@ -2625,6 +2625,9 @@ 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>
diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml
index 5b58657..476f448 100644
--- a/Documentation/DocBook/media/v4l/io.xml
+++ b/Documentation/DocBook/media/v4l/io.xml
@@ -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 a 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
diff --git a/Documentation/DocBook/media/v4l/v4l2.xml b/Documentation/DocBook/media/v4l/v4l2.xml
index eee6908..d8c2597 100644
--- a/Documentation/DocBook/media/v4l/v4l2.xml
+++ b/Documentation/DocBook/media/v4l/v4l2.xml
@@ -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;
diff --git a/Documentation/DocBook/media/v4l/vidioc-expbuf.xml b/Documentation/DocBook/media/v4l/vidioc-expbuf.xml
new file mode 100644
index 0000000..bf28e7d
--- /dev/null
+++ b/Documentation/DocBook/media/v4l/vidioc-expbuf.xml
@@ -0,0 +1,212 @@
+<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, applicationis 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 multi plane 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 currently active
+format. For single plane 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 a 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 API. Refer to <link
+linkend="dmabuf">DMABUF importing</link> for details about importing DMABUF
+files into V4L2 nodes. A developer is encouraged to close a DMABUF file when it
+is no longer used to avoid a resource leak. </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(&expbuf, 0, sizeof expbuf);
+ expbuf.type = bt;
+ expbuf.index = index;
+ if (ioctl(v4lfd, &VIDIOC-EXPBUF;, &expbuf) == -1) {
+ perror("VIDIOC_EXPBUF");
+ return -1;
+ }
+
+ *dmafd = expbuf.fd;
+
+ return 0;
+}
+ </programlisting>
+ </example>
+
+ <example>
+ <title>Exporting a buffer using multi plane 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 < n_planes; ++i) {
+ &v4l2-exportbuffer; expbuf;
+
+ memset(&expbuf, 0, sizeof expbuf);
+ expbuf.type = bt;
+ expbuf.index = index;
+ expbuf.plane = i;
+ if (ioctl(v4lfd, &VIDIOC-EXPBUF;, &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>__s32</entry>
+ <entry><structfield>fd</structfield></entry>
+ <entry>The DMABUF file descriptor associated with a buffer. Set by
+ a driver.</entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>flags</structfield></entry>
+ <entry>Flags for newly created file, currently only <constant>
+O_CLOEXEC </constant> is supported, refer to the manual of open() for more
+details.</entry>
+ </row>
+ <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; ioctl
+(&v4l2-requestbuffers; <structfield>count</structfield>) minus one.</entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>plane</structfield></entry>
+ <entry>Index of the plane to be exported when using multi plane
+API. Otherwise this value must be set to zero. </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>
--
1.7.9.5
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