diff options
Diffstat (limited to 'Documentation/DocBook')
| -rw-r--r-- | Documentation/DocBook/media/v4l/vidioc-create-bufs.xml | 30 |
1 files changed, 14 insertions, 16 deletions
diff --git a/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml b/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml index 8ffe74f84af1..d81fa0d4016b 100644 --- a/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml +++ b/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml @@ -58,7 +58,7 @@ <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 +addition to the &VIDIOC-REQBUFS; ioctl, when a tighter control over buffers is required. This ioctl can be called multiple times to create buffers of different sizes.</para> @@ -71,30 +71,28 @@ 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> +&v4l2-format;. Usually this will be done using the &VIDIOC-TRY-FMT; or &VIDIOC-G-FMT; ioctls +to ensure that the requested format is supported by the driver. +Based on the format's <structfield>type</structfield> field the requested buffer +size (for single-planar) or plane sizes (for multi-planar formats) will be +used for the allocated buffers. The driver may return an error if the size(s) +are not supported by the hardware (usually because they are too small).</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 +defined by the <structfield>format.pix.sizeimage</structfield> field (or the +corresponding fields for other format types). Usually 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> +required for the given format, then an error will be returned since drivers will +typically not allow this. If it is larger, then the value will be used as-is. +In other words, the driver may reject the requested size, but if it is accepted +the driver will use it unchanged.</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> +the number requested.</para> <table pgwide="1" frame="none" id="v4l2-create-buffers"> <title>struct <structname>v4l2_create_buffers</structname></title> |