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Diffstat (limited to 'kernel/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml')
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1 files changed, 165 insertions, 0 deletions
diff --git a/kernel/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml b/kernel/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml new file mode 100644 index 000000000..9b700a5f4 --- /dev/null +++ b/kernel/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml @@ -0,0 +1,165 @@ +<refentry id="vidioc-create-bufs"> + <refmeta> + <refentrytitle>ioctl VIDIOC_CREATE_BUFS</refentrytitle> + &manvol; + </refmeta> + + <refnamediv> + <refname>VIDIOC_CREATE_BUFS</refname> + <refpurpose>Create buffers for Memory Mapped or User Pointer or DMA Buffer + I/O</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_create_buffers *<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_CREATE_BUFS</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 used to create buffers for <link linkend="mmap">memory +mapped</link> or <link linkend="userp">user pointer</link> or <link +linkend="dmabuf">DMA buffer</link> I/O. It can be used as an alternative or in +addition to the <constant>VIDIOC_REQBUFS</constant> ioctl, when a tighter +control over buffers is required. This ioctl can be called multiple times to +create buffers of different sizes.</para> + + <para>To allocate the device buffers applications must initialize the +relevant fields of the <structname>v4l2_create_buffers</structname> structure. +The <structfield>count</structfield> field must be set to the number of +requested buffers, the <structfield>memory</structfield> field specifies the +requested I/O method and the <structfield>reserved</structfield> array must be +zeroed.</para> + + <para>The <structfield>format</structfield> field specifies the image format +that the buffers must be able to handle. The application has to fill in this +&v4l2-format;. Usually this will be done using the +<constant>VIDIOC_TRY_FMT</constant> or <constant>VIDIOC_G_FMT</constant> ioctl() +to ensure that the requested format is supported by the driver. Unsupported +formats will result in an error.</para> + + <para>The buffers created by this ioctl will have as minimum size the size +defined by the <structfield>format.pix.sizeimage</structfield> field. If the +<structfield>format.pix.sizeimage</structfield> field is less than the minimum +required for the given format, then <structfield>sizeimage</structfield> will be +increased by the driver to that minimum to allocate the buffers. If it is +larger, then the value will be used as-is. The same applies to the +<structfield>sizeimage</structfield> field of the +<structname>v4l2_plane_pix_format</structname> structure in the case of +multiplanar formats.</para> + + <para>When the ioctl is called with a pointer to this structure the driver +will attempt to allocate up to the requested number of buffers and store the +actual number allocated and the starting index in the +<structfield>count</structfield> and the <structfield>index</structfield> fields +respectively. On return <structfield>count</structfield> can be smaller than +the number requested. The driver may also increase buffer sizes if required, +however, it will not update <structfield>sizeimage</structfield> field values. +The user has to use <constant>VIDIOC_QUERYBUF</constant> to retrieve that +information.</para> + + <table pgwide="1" frame="none" id="v4l2-create-buffers"> + <title>struct <structname>v4l2_create_buffers</structname></title> + <tgroup cols="3"> + &cs-str; + <tbody valign="top"> + <row> + <entry>__u32</entry> + <entry><structfield>index</structfield></entry> + <entry>The starting buffer index, returned by the driver.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>count</structfield></entry> + <entry>The number of buffers requested or granted. If count == 0, then + <constant>VIDIOC_CREATE_BUFS</constant> will set <structfield>index</structfield> + to the current number of created buffers, and it will check the validity of + <structfield>memory</structfield> and <structfield>format.type</structfield>. + If those are invalid -1 is returned and errno is set to &EINVAL;, + otherwise <constant>VIDIOC_CREATE_BUFS</constant> returns 0. It will + never set errno to &EBUSY; in this particular case.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>memory</structfield></entry> + <entry>Applications set this field to +<constant>V4L2_MEMORY_MMAP</constant>, +<constant>V4L2_MEMORY_DMABUF</constant> or +<constant>V4L2_MEMORY_USERPTR</constant>. See <xref linkend="v4l2-memory" +/></entry> + </row> + <row> + <entry>&v4l2-format;</entry> + <entry><structfield>format</structfield></entry> + <entry>Filled in by the application, preserved by the driver.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>reserved</structfield>[8]</entry> + <entry>A place holder for future extensions.</entry> + </row> + </tbody> + </tgroup> + </table> + </refsect1> + + <refsect1> + &return-value; + + <variablelist> + <varlistentry> + <term><errorcode>ENOMEM</errorcode></term> + <listitem> + <para>No memory to allocate buffers for <link linkend="mmap">memory +mapped</link> I/O.</para> + </listitem> + </varlistentry> + <varlistentry> + <term><errorcode>EINVAL</errorcode></term> + <listitem> + <para>The buffer type (<structfield>format.type</structfield> field), +requested I/O method (<structfield>memory</structfield>) or format +(<structfield>format</structfield> field) is not valid.</para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> +</refentry> |