This patch adds description and usage examples for importing DMABUF file descriptor in V4L2.
Signed-off-by: Tomasz Stanislawski t.stanislaws@samsung.com Signed-off-by: Kyungmin Park kyungmin.park@samsung.com CC: linux-doc@vger.kernel.org --- Documentation/DocBook/media/v4l/compat.xml | 4 + Documentation/DocBook/media/v4l/io.xml | 179 ++++++++++++++++++++ .../DocBook/media/v4l/vidioc-create-bufs.xml | 1 + Documentation/DocBook/media/v4l/vidioc-qbuf.xml | 15 ++ Documentation/DocBook/media/v4l/vidioc-reqbufs.xml | 45 ++--- 5 files changed, 223 insertions(+), 21 deletions(-)
diff --git a/Documentation/DocBook/media/v4l/compat.xml b/Documentation/DocBook/media/v4l/compat.xml index ea42ef8..07a311f 100644 --- a/Documentation/DocBook/media/v4l/compat.xml +++ b/Documentation/DocBook/media/v4l/compat.xml @@ -2587,6 +2587,10 @@ ioctls.</para> <para><link linkend="v4l2-auto-focus-area"><constant> V4L2_CID_AUTO_FOCUS_AREA</constant></link> control.</para> </listitem> + <listitem> + <para>Importing DMABUF file descriptors as a new IO method described + in <xref linkend="dmabuf" />.</para> + </listitem> </itemizedlist> </section>
diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml index fd6aca2..521f699 100644 --- a/Documentation/DocBook/media/v4l/io.xml +++ b/Documentation/DocBook/media/v4l/io.xml @@ -472,6 +472,162 @@ rest should be evident.</para> </footnote></para> </section>
+ <section id="dmabuf"> + <title>Streaming I/O (DMA buffer importing)</title> + + <note> + <title>Experimental</title> + <para>This is an <link linkend="experimental"> experimental </link> + interface and may change in the future.</para> + </note> + +<para>The DMABUF framework provides a generic mean for sharing buffers between + multiple devices. Device drivers that support DMABUF can export a DMA buffer +to userspace as a file descriptor (known as the exporter role), import a DMA +buffer from userspace using a file descriptor previously exported for a +different or the same device (known as the importer role), or both. This +section describes the DMABUF importer role API in V4L2.</para> + +<para>Input and output devices support the streaming I/O method when the +<constant>V4L2_CAP_STREAMING</constant> flag in the +<structfield>capabilities</structfield> field of &v4l2-capability; returned by +the &VIDIOC-QUERYCAP; ioctl is set. Whether importing DMA buffers through +DMABUF file descriptors is supported is determined by calling the +&VIDIOC-REQBUFS; ioctl with the memory type set to +<constant>V4L2_MEMORY_DMABUF</constant>.</para> + + <para>This I/O method is dedicated for sharing DMA buffers between V4L and +other APIs. Buffers (planes) are allocated by a driver on behalf of the +application, and exported to the application as file descriptors using an API +specific to the allocator driver. Only those file descriptor are exchanged, +these files and meta-information are passed in &v4l2-buffer; (or in +&v4l2-plane; in the multi-planar API case). The driver must be switched into +DMABUF I/O mode by calling the &VIDIOC-REQBUFS; with the desired buffer type. +No buffers (planes) are allocated beforehand, consequently they are not indexed +and cannot be queried like mapped buffers with the +<constant>VIDIOC_QUERYBUF</constant> ioctl.</para> + + <example> + <title>Initiating streaming I/O with DMABUF file descriptors</title> + + <programlisting> +&v4l2-requestbuffers; reqbuf; + +memset (&reqbuf, 0, sizeof (reqbuf)); +reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; +reqbuf.memory = V4L2_MEMORY_DMABUF; + +if (ioctl (fd, &VIDIOC-REQBUFS;, &reqbuf) == -1) { + if (errno == EINVAL) + printf ("Video capturing or DMABUF streaming is not supported\n"); + else + perror ("VIDIOC_REQBUFS"); + + exit (EXIT_FAILURE); +} + </programlisting> + </example> + + <para>Buffer (plane) file is passed on the fly with the &VIDIOC-QBUF; +ioctl. In case of multiplanar buffers, every plane can be associated with a +different DMABUF descriptor.Although buffers are commonly cycled, applications +can pass different DMABUF descriptor at each <constant>VIDIOC_QBUF</constant> +call.</para> + + <example> + <title>Queueing DMABUF using single plane API</title> + + <programlisting> +int buffer_queue(int v4lfd, int index, int dmafd) +{ + &v4l2-buffer; buf; + + memset(&buf, 0, sizeof buf); + buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; + buf.memory = V4L2_MEMORY_DMABUF; + buf.index = index; + buf.m.fd = dmafd; + + if (ioctl (v4lfd, &VIDIOC-QBUF;, &buf) == -1) { + perror ("VIDIOC_QBUF"); + return -1; + } + + return 0; +} + </programlisting> + </example> + + <example> + <title>Queueing DMABUF using multi plane API</title> + + <programlisting> +int buffer_queue_mp(int v4lfd, int index, int dmafd[], int n_planes) +{ + &v4l2-buffer; buf; + &v4l2-plane; planes[VIDEO_MAX_PLANES]; + int i; + + memset(&buf, 0, sizeof buf); + buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE; + buf.memory = V4L2_MEMORY_DMABUF; + buf.index = index; + buf.m.planes = planes; + buf.length = n_planes; + + memset(&planes, 0, sizeof planes); + + for (i = 0; i < n_planes; ++i) + buf.m.planes[i].m.fd = dmafd[i]; + + if (ioctl (v4lfd, &VIDIOC-QBUF;, &buf) == -1) { + perror ("VIDIOC_QBUF"); + return -1; + } + + return 0; +} + </programlisting> + </example> + + <para>Filled or displayed buffers are dequeued with the +&VIDIOC-DQBUF; ioctl. The driver can unlock the buffer at any +time between the completion of the DMA and this ioctl. The memory is +also unlocked when &VIDIOC-STREAMOFF; is called, &VIDIOC-REQBUFS;, or +when the device is closed.</para> + + <para>For capturing applications it is customary to enqueue a +number of empty buffers, to start capturing and enter the read loop. +Here the application waits until a filled buffer can be dequeued, and +re-enqueues the buffer when the data is no longer needed. Output +applications fill and enqueue buffers, when enough buffers are stacked +up output is started. In the write loop, when the application +runs out of free buffers it must wait until an empty buffer can be +dequeued and reused. Two methods exist to suspend execution of the +application until one or more buffers can be dequeued. By default +<constant>VIDIOC_DQBUF</constant> blocks when no buffer is in the +outgoing queue. When the <constant>O_NONBLOCK</constant> flag was +given to the &func-open; function, <constant>VIDIOC_DQBUF</constant> +returns immediately with an &EAGAIN; when no buffer is available. The +&func-select; or &func-poll; function are always available.</para> + + <para>To start and stop capturing or output applications call the +&VIDIOC-STREAMON; and &VIDIOC-STREAMOFF; ioctls. Note that +<constant>VIDIOC_STREAMOFF</constant> removes all buffers from both queues and +unlocks all buffers as a side effect. Since there is no notion of doing +anything "now" on a multitasking system, if an application needs to synchronize +with another event it should examine the &v4l2-buffer; +<structfield>timestamp</structfield> of captured buffers, or set the field +before enqueuing buffers for output.</para> + + <para>Drivers implementing DMABUF importing I/O must support the +<constant>VIDIOC_REQBUFS</constant>, <constant>VIDIOC_QBUF</constant>, +<constant>VIDIOC_DQBUF</constant>, <constant>VIDIOC_STREAMON</constant> and +<constant>VIDIOC_STREAMOFF</constant> ioctl, the <function>select()</function> +and <function>poll()</function> function.</para> + + </section> + <section id="async"> <title>Asynchronous I/O</title>
@@ -673,6 +829,14 @@ memory, set by the application. See <xref linkend="userp" /> for details. <structname>v4l2_buffer</structname> structure.</entry> </row> <row> + <entry></entry> + <entry>int</entry> + <entry><structfield>fd</structfield></entry> + <entry>For the single-plane API and when +<structfield>memory</structfield> is <constant>V4L2_MEMORY_DMABUF</constant> this +is the file descriptor associated with a DMABUF buffer.</entry> + </row> + <row> <entry>__u32</entry> <entry><structfield>length</structfield></entry> <entry></entry> @@ -748,6 +912,15 @@ should set this to 0.</entry> </entry> </row> <row> + <entry></entry> + <entry>int</entry> + <entry><structfield>fd</structfield></entry> + <entry>When the memory type in the containing &v4l2-buffer; is + <constant>V4L2_MEMORY_DMABUF</constant>, this is a file + descriptor associated with a DMABUF buffer, similar to the + <structfield>fd</structfield> field in &v4l2-buffer;.</entry> + </row> + <row> <entry>__u32</entry> <entry><structfield>data_offset</structfield></entry> <entry></entry> @@ -982,6 +1155,12 @@ pointer</link> I/O.</entry> <entry>3</entry> <entry>[to do]</entry> </row> + <row> + <entry><constant>V4L2_MEMORY_DMABUF</constant></entry> + <entry>2</entry> + <entry>The buffer is used for <link linkend="dmabuf">DMA shared +buffer</link> I/O.</entry> + </row> </tbody> </tgroup> </table> diff --git a/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml b/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml index 765549f..fee66ac 100644 --- a/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml +++ b/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml @@ -104,6 +104,7 @@ information.</para> <entry><structfield>memory</structfield></entry> <entry>Applications set this field to <constant>V4L2_MEMORY_MMAP</constant> or +<constant>V4L2_MEMORY_DMABUF</constant> or <constant>V4L2_MEMORY_USERPTR</constant>. See <xref linkend="v4l2-memory" /></entry> </row> diff --git a/Documentation/DocBook/media/v4l/vidioc-qbuf.xml b/Documentation/DocBook/media/v4l/vidioc-qbuf.xml index 9caa49a..cb5f5ff 100644 --- a/Documentation/DocBook/media/v4l/vidioc-qbuf.xml +++ b/Documentation/DocBook/media/v4l/vidioc-qbuf.xml @@ -112,6 +112,21 @@ they cannot be swapped out to disk. Buffers remain locked until dequeued, until the &VIDIOC-STREAMOFF; or &VIDIOC-REQBUFS; ioctl is called, or until the device is closed.</para>
+ <para>To enqueue a <link linkend="dmabuf">DMABUF</link> buffer applications +set the <structfield>memory</structfield> field to +<constant>V4L2_MEMORY_DMABUF</constant> and the <structfield>m.fd</structfield> +to a file descriptor associated with a DMABUF buffer. When the multi-planar API is +used and <structfield>m.fd</structfield> of the passed array of &v4l2-plane; +have to be used instead. 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 +<constant>V4L2_BUF_FLAG_DONE</constant> flags in the +<structfield>flags</structfield> field, or it returns an error code. This +ioctl locks the buffer. Buffers remain locked until 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 diff --git a/Documentation/DocBook/media/v4l/vidioc-reqbufs.xml b/Documentation/DocBook/media/v4l/vidioc-reqbufs.xml index d7c9505..13381ea 100644 --- a/Documentation/DocBook/media/v4l/vidioc-reqbufs.xml +++ b/Documentation/DocBook/media/v4l/vidioc-reqbufs.xml @@ -48,28 +48,30 @@ <refsect1> <title>Description</title>
- <para>This ioctl is used to initiate <link linkend="mmap">memory -mapped</link> or <link linkend="userp">user pointer</link> -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 and to setup some internal structures.</para> +<para>This ioctl is used to initiate <link linkend="mmap">memory mapped</link>, +<link linkend="userp">user pointer</link> or <link +linkend="dmabuf">DMABUF</link> based 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 and to setup some internal structures. +Similarly, DMABUF buffers are allocated by applications through a device +driver, and this ioctl only configures the driver into DMABUF I/O mode without +performing any direct allocation.</para>
- <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, <structfield>memory</structfield> -must be set to the requested I/O method and the <structfield>reserved</structfield> 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 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> + <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, +<structfield>memory</structfield> must be set to the requested I/O method and +the <structfield>reserved</structfield> 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 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> <para>When the I/O method is not supported the ioctl returns an &EINVAL;.</para>
@@ -103,6 +105,7 @@ as the &v4l2-format; <structfield>type</structfield> field. See <xref <entry><structfield>memory</structfield></entry> <entry>Applications set this field to <constant>V4L2_MEMORY_MMAP</constant> or +<constant>V4L2_MEMORY_DMABUF</constant> or <constant>V4L2_MEMORY_USERPTR</constant>. See <xref linkend="v4l2-memory" />.</entry> </row>