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authorHans Verkuil <hans.verkuil@cisco.com>2015-10-29 05:07:30 +0100
committerMauro Carvalho Chehab <mchehab@osg.samsung.com>2015-12-18 16:49:27 +0100
commit02a34b6ace4cce92d5cf4d76e54afe0c71e4f706 (patch)
treeb2f9218ec027880178a16ba333d1d4486972070c /Documentation/DocBook
parent[media] vb2: drop v4l2_format argument from queue_setup (diff)
downloadlinux-02a34b6ace4cce92d5cf4d76e54afe0c71e4f706.tar.xz
linux-02a34b6ace4cce92d5cf4d76e54afe0c71e4f706.zip
[media] DocBook media: update VIDIOC_CREATE_BUFS documentation
During the Seoul media workshop we decided to relax the VIDIOC_CREATE_BUFS specification so it would no longer require drivers to validate the format field since almost no driver did that anyway. Instead drivers use the buffer size(s) based on the format type and the corresponding format fields and will ignore any other fields. If the size cannot be used an error is returned, otherwise the size is used as-is. Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Diffstat (limited to 'Documentation/DocBook')
-rw-r--r--Documentation/DocBook/media/v4l/vidioc-create-bufs.xml30
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>