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V4L/DVB: media-spec: Fix documentation mistakes regarding I/O streaming

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The media spec contains several errors in the description of the
I/O streaming ioctls, in particular with respect to the userptr
I/O method.

The most important change is that you really need to set count
and index in v4l2_requestbuffer and v4l2_buffer when dealing with
user pointer streaming.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Hans Verkuil 2010-02-20 09:41:03 -03:00 committed by Mauro Carvalho Chehab
parent 340dde817a
commit 995f5fefb0
4 changed files with 42 additions and 44 deletions
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3
Documentation/DocBook/v4l/io.xml
View File

@ -589,7 +589,8 @@ number of a video input as in &v4l2-input; field
<entry></entry>
<entry>A place holder for future extensions and custom
(driver defined) buffer types
<constant>V4L2_BUF_TYPE_PRIVATE</constant> and higher.</entry>
<constant>V4L2_BUF_TYPE_PRIVATE</constant> and higher. Applications
should set this to 0.</entry>
</row>
</tbody>
</tgroup>

40
Documentation/DocBook/v4l/vidioc-qbuf.xml
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@ -54,12 +54,10 @@ to enqueue an empty (capturing) or filled (output) buffer in the
driver's incoming queue. The semantics depend on the selected I/O
method.</para>
<para>To enqueue a <link linkend="mmap">memory mapped</link>
buffer applications set the <structfield>type</structfield> field of a
&v4l2-buffer; to the same buffer type as previously &v4l2-format;
<structfield>type</structfield> and &v4l2-requestbuffers;
<structfield>type</structfield>, the <structfield>memory</structfield>
field to <constant>V4L2_MEMORY_MMAP</constant> and the
<para>To enqueue a buffer applications set the <structfield>type</structfield>
field of a &v4l2-buffer; to the same buffer type as was previously used
with &v4l2-format; <structfield>type</structfield> and &v4l2-requestbuffers;
<structfield>type</structfield>. Applications must also set the
<structfield>index</structfield> field. Valid index numbers range from
zero to the number of buffers allocated with &VIDIOC-REQBUFS;
(&v4l2-requestbuffers; <structfield>count</structfield>) minus one. The
@ -70,8 +68,19 @@ intended for output (<structfield>type</structfield> is
<constant>V4L2_BUF_TYPE_VBI_OUTPUT</constant>) applications must also
initialize the <structfield>bytesused</structfield>,
<structfield>field</structfield> and
<structfield>timestamp</structfield> fields. See <xref
linkend="buffer" /> for details. When
<structfield>timestamp</structfield> fields, see <xref
linkend="buffer" /> for details.
Applications must also set <structfield>flags</structfield> to 0. If a driver
supports capturing from specific video inputs and you want to specify a video
input, then <structfield>flags</structfield> should be set to
<constant>V4L2_BUF_FLAG_INPUT</constant> and the field
<structfield>input</structfield> must be initialized to the desired input.
The <structfield>reserved</structfield> field must be set to 0.
</para>
<para>To enqueue a <link linkend="mmap">memory mapped</link>
buffer applications set the <structfield>memory</structfield>
field to <constant>V4L2_MEMORY_MMAP</constant>. When
<constant>VIDIOC_QBUF</constant> is called with a pointer to this
structure the driver sets the
<constant>V4L2_BUF_FLAG_MAPPED</constant> and
@ -81,14 +90,10 @@ structure the driver sets the
&EINVAL;.</para>
<para>To enqueue a <link linkend="userp">user pointer</link>
buffer applications set the <structfield>type</structfield> field of a
&v4l2-buffer; to the same buffer type as previously &v4l2-format;
<structfield>type</structfield> and &v4l2-requestbuffers;
<structfield>type</structfield>, the <structfield>memory</structfield>
field to <constant>V4L2_MEMORY_USERPTR</constant> and the
buffer applications set the <structfield>memory</structfield>
field to <constant>V4L2_MEMORY_USERPTR</constant>, the
<structfield>m.userptr</structfield> field to the address of the
buffer and <structfield>length</structfield> to its size. When the
buffer is intended for output additional fields must be set as above.
buffer and <structfield>length</structfield> to its size.
When <constant>VIDIOC_QBUF</constant> is called with a pointer to this
structure the driver sets the <constant>V4L2_BUF_FLAG_QUEUED</constant>
flag and clears the <constant>V4L2_BUF_FLAG_MAPPED</constant> and
@ -96,13 +101,14 @@ flag and clears the <constant>V4L2_BUF_FLAG_MAPPED</constant> and
<structfield>flags</structfield> field, or it returns an error code.
This ioctl locks the memory pages of the buffer in physical memory,
they cannot be swapped out to disk. Buffers remain locked until
dequeued, until the &VIDIOC-STREAMOFF; or &VIDIOC-REQBUFS; ioctl are
dequeued, until the &VIDIOC-STREAMOFF; or &VIDIOC-REQBUFS; ioctl is
called, or until the device is closed.</para>
<para>Applications call the <constant>VIDIOC_DQBUF</constant>
ioctl to dequeue a filled (capturing) or displayed (output) buffer
from the driver's outgoing queue. They just set the
<structfield>type</structfield> and <structfield>memory</structfield>
<structfield>type</structfield>, <structfield>memory</structfield>
and <structfield>reserved</structfield>
fields of a &v4l2-buffer; as above, when <constant>VIDIOC_DQBUF</constant>
is called with a pointer to this structure the driver fills the
remaining fields or returns an error code.</para>

7
Documentation/DocBook/v4l/vidioc-querybuf.xml
View File

@ -54,12 +54,13 @@ buffer at any time after buffers have been allocated with the
&VIDIOC-REQBUFS; ioctl.</para>
<para>Applications set the <structfield>type</structfield> field
of a &v4l2-buffer; to the same buffer type as previously
of a &v4l2-buffer; to the same buffer type as was previously used with
&v4l2-format; <structfield>type</structfield> and &v4l2-requestbuffers;
<structfield>type</structfield>, and the <structfield>index</structfield>
field. Valid index numbers range from zero
to the number of buffers allocated with &VIDIOC-REQBUFS;
(&v4l2-requestbuffers; <structfield>count</structfield>) minus one.
The <structfield>reserved</structfield> field should to set to 0.
After calling <constant>VIDIOC_QUERYBUF</constant> with a pointer to
this structure drivers return an error code or fill the rest of
the structure.</para>
@ -68,8 +69,8 @@ the structure.</para>
<constant>V4L2_BUF_FLAG_MAPPED</constant>,
<constant>V4L2_BUF_FLAG_QUEUED</constant> and
<constant>V4L2_BUF_FLAG_DONE</constant> flags will be valid. The
<structfield>memory</structfield> field will be set to
<constant>V4L2_MEMORY_MMAP</constant>, the <structfield>m.offset</structfield>
<structfield>memory</structfield> field will be set to the current
I/O method, the <structfield>m.offset</structfield>
contains the offset of the buffer from the start of the device memory,
the <structfield>length</structfield> field its size. The driver may
or may not set the remaining fields and flags, they are meaningless in

36
Documentation/DocBook/v4l/vidioc-reqbufs.xml
View File

@ -54,23 +54,23 @@ I/O. Memory mapped buffers are located in device memory and must be
allocated with this ioctl before they can be mapped into the
application's address space. User buffers are allocated by
applications themselves, and this ioctl is merely used to switch the
driver into user pointer I/O mode.</para>
driver into user pointer I/O mode and to setup some internal structures.</para>
<para>To allocate device buffers applications initialize three
fields of a <structname>v4l2_requestbuffers</structname> structure.
<para>To allocate device buffers applications initialize all
fields of the <structname>v4l2_requestbuffers</structname> structure.
They set the <structfield>type</structfield> field to the respective
stream or buffer type, the <structfield>count</structfield> field to
the desired number of buffers, and <structfield>memory</structfield>
must be set to <constant>V4L2_MEMORY_MMAP</constant>. When the ioctl
is called with a pointer to this structure the driver attempts to
allocate the requested number of buffers and stores the actual number
the desired number of buffers, <structfield>memory</structfield>
must be set to the requested I/O method and the reserved array
must be zeroed. When the ioctl
is called with a pointer to this structure the driver will attempt to allocate
the requested number of buffers and it stores the actual number
allocated in the <structfield>count</structfield> field. It can be
smaller than the number requested, even zero, when the driver runs out
of free memory. A larger number is possible when the driver requires
more buffers to function correctly.<footnote>
<para>For example video output requires at least two buffers,
of free memory. A larger number is also possible when the driver requires
more buffers to function correctly. For example video output requires at least two buffers,
one displayed and one filled by the application.</para>
</footnote> When memory mapping I/O is not supported the ioctl
<para>When the I/O method is not supported the ioctl
returns an &EINVAL;.</para>
<para>Applications can call <constant>VIDIOC_REQBUFS</constant>
@ -81,14 +81,6 @@ in progress, an implicit &VIDIOC-STREAMOFF;. <!-- mhs: I see no
reason why munmap()ping one or even all buffers must imply
streamoff.--></para>
<para>To negotiate user pointer I/O, applications initialize only
the <structfield>type</structfield> field and set
<structfield>memory</structfield> to
<constant>V4L2_MEMORY_USERPTR</constant>. When the ioctl is called
with a pointer to this structure the driver prepares for user pointer
I/O, when this I/O method is not supported the ioctl returns an
&EINVAL;.</para>
<table pgwide="1" frame="none" id="v4l2-requestbuffers">
<title>struct <structname>v4l2_requestbuffers</structname></title>
<tgroup cols="3">
@ -97,9 +89,7 @@ I/O, when this I/O method is not supported the ioctl returns an
<row>
<entry>__u32</entry>
<entry><structfield>count</structfield></entry>
<entry>The number of buffers requested or granted. This
field is only used when <structfield>memory</structfield> is set to
<constant>V4L2_MEMORY_MMAP</constant>.</entry>
<entry>The number of buffers requested or granted.</entry>
</row>
<row>
<entry>&v4l2-buf-type;</entry>
@ -120,7 +110,7 @@ as the &v4l2-format; <structfield>type</structfield> field. See <xref
<entry><structfield>reserved</structfield>[2]</entry>
<entry>A place holder for future extensions and custom
(driver defined) buffer types <constant>V4L2_BUF_TYPE_PRIVATE</constant> and
higher.</entry>
higher. This array should be zeroed by applications.</entry>
</row>
</tbody>
</tgroup>