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[media] Documentation: media: Clarify the VIDIOC_CREATE_BUFS format requirements

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The VIDIOC_CREATE_BUFS ioctl takes a format argument that must contain a
valid format supported by the driver. Clarify the documentation.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
This commit is contained in:
Laurent Pinchart 2013-08-01 21:34:52 -03:00 committed by Mauro Carvalho Chehab
parent 5c7b25b90d
commit c09aada7ac
1 changed files with 26 additions and 15 deletions
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41
Documentation/DocBook/media/v4l/vidioc-create-bufs.xml
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@ -62,18 +62,29 @@ 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 device buffers applications initialize relevant fields of
the <structname>v4l2_create_buffers</structname> structure. They set the
<structfield>type</structfield> field in the
&v4l2-format; structure, embedded in this
structure, to the respective stream or buffer type.
<structfield>count</structfield> must be set to the number of required buffers.
<structfield>memory</structfield> specifies the required I/O method. The
<structfield>format</structfield> field shall typically be filled in using
either the <constant>VIDIOC_TRY_FMT</constant> or
<constant>VIDIOC_G_FMT</constant> ioctl(). Additionally, applications can adjust
<structfield>sizeimage</structfield> fields to fit their specific needs. The
<structfield>reserved</structfield> array must be zeroed.</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
@ -144,9 +155,9 @@ mapped</link> I/O.</para>
<varlistentry>
<term><errorcode>EINVAL</errorcode></term>
<listitem>
<para>The buffer type (<structfield>type</structfield> field) or the
requested I/O method (<structfield>memory</structfield>) is not
supported.</para>
<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>