diff options
Diffstat (limited to 'Documentation/DocBook/media/v4l/vidioc-create-bufs.xml')
| -rw-r--r-- | Documentation/DocBook/media/v4l/vidioc-create-bufs.xml | 41 |
1 files changed, 26 insertions, 15 deletions
diff --git a/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml b/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml index cd9943672434..9b700a5f4df7 100644 --- a/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml +++ b/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml @@ -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> |