Re: [PATCH v3] V4L: add two new ioctl()s for multi-size videobuffer management

From: Sakari Ailus <sakari.ailus@iki.fi>
To: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Cc: Linux Media Mailing List <linux-media@vger.kernel.org>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Hans Verkuil <hverkuil@xs4all.nl>,
	Mauro Carvalho Chehab <mchehab@infradead.org>,
	Pawel Osciak <pawel@osciak.com>
Subject: Re: [PATCH v3] V4L: add two new ioctl()s for multi-size videobuffer management
Date: Wed, 20 Jul 2011 17:30:28 +0300	[thread overview]
Message-ID: <20110720143028.GG29320@valkosipuli.localdomain> (raw)
In-Reply-To: <Pine.LNX.4.64.1107201025120.12084@axis700.grange>

Hi, Guennadi!

Thanks for the patch!

On Wed, Jul 20, 2011 at 10:43:08AM +0200, Guennadi Liakhovetski wrote:
> A possibility to preallocate and initialise buffers of different sizes
> in V4L2 is required for an efficient implementation of asnapshot mode.
> This patch adds two new ioctl()s: VIDIOC_CREATE_BUFS and
> VIDIOC_PREPARE_BUF and defines respective data structures.
> 
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> ---
> 
> It's been almost a month since v2, the only comments were a request to 
> increase the reserved space in the new ioctl() and to improve 
> documentation. The reserved field is increased in this version, 
> documentation also has been improved in multiple locations. I think, 
> documentation can be further improved at any time, but if there are no 
> objections against the actual contents of this patch, maybe we can commit 
> this version. I still don't see v3.0;-), so, maybe we even can push it for 
> 3.1. A trivial comparison with v2 shows the size of the reserved field as 
> the only change in the API, and the compatibility fix as the only two 
> functional changes.
> 
> v3: addressed multiple comments by Sakari Ailus
> 
> 1. increased reserved field in "struct v4l2_create_buffers" to 8 32-bit 
>    ints
> 2. multiple documentation fixes and improvements
> 3. fixed misplaced "case VIDIOC_PREPARE_BUF" in ioctl 32-bit compatibility 
>    processing
> 
> v2:
> 
> 1. add preliminary Documentation
> 2. add flag V4L2_BUFFER_FLAG_NO_CACHE_CLEAN
> 3. remove VIDIOC_DESTROY_BUFS
> 4. rename SUBMIT to VIDIOC_PREPARE_BUF
> 5. add reserved field to struct v4l2_create_buffers
> 6. cache handling flags moved to struct v4l2_buffer for processing during 
>    VIDIOC_PREPARE_BUF
> 7. VIDIOC_PREPARE_BUF now uses struct v4l2_buffer as its argument
> 
> 
>  Documentation/DocBook/media/v4l/io.xml             |   17 +++
>  Documentation/DocBook/media/v4l/v4l2.xml           |    2 +
>  .../DocBook/media/v4l/vidioc-create-bufs.xml       |  152 ++++++++++++++++++++
>  .../DocBook/media/v4l/vidioc-prepare-buf.xml       |   96 ++++++++++++
>  drivers/media/video/v4l2-compat-ioctl32.c          |   68 ++++++++-
>  drivers/media/video/v4l2-ioctl.c                   |   32 ++++
>  include/linux/videodev2.h                          |   16 ++
>  include/media/v4l2-ioctl.h                         |    2 +
>  8 files changed, 377 insertions(+), 8 deletions(-)
>  create mode 100644 Documentation/DocBook/media/v4l/vidioc-create-bufs.xml
>  create mode 100644 Documentation/DocBook/media/v4l/vidioc-prepare-buf.xml
> 
> diff --git a/Documentation/DocBook/media/v4l/io.xml b/Documentation/DocBook/media/v4l/io.xml
> index 227e7ac..6249d0e 100644
> --- a/Documentation/DocBook/media/v4l/io.xml
> +++ b/Documentation/DocBook/media/v4l/io.xml
> @@ -927,6 +927,23 @@ ioctl is called.</entry>
>  Applications set or clear this flag before calling the
>  <constant>VIDIOC_QBUF</constant> ioctl.</entry>
>  	  </row>
> +	  <row>
> +	    <entry><constant>V4L2_BUF_FLAG_NO_CACHE_INVALIDATE</constant></entry>
> +	    <entry>0x0400</entry>
> +	    <entry>Caches do not have to be invalidated for this buffer.
> +Typically applications shall use this flag, if the data, captured in the buffer
> +is not going to br touched by the CPU, instead the buffer will, probably, be
> +passed on to a DMA-capable hardware unit for further processing or output.
> +</entry>
> +	  </row>
> +	  <row>
> +	    <entry><constant>V4L2_BUF_FLAG_NO_CACHE_CLEAN</constant></entry>
> +	    <entry>0x0800</entry>
> +	    <entry>Caches do not have to be cleaned for this buffer.
> +Typically applications shall use this flag for output buffers, if the data
> +in this buffer has not been created by the CPU, but by some DMA-capable unit,
> +in which case caches have not been used.</entry>
> +	  </row>
>  	</tbody>
>        </tgroup>
>      </table>
> diff --git a/Documentation/DocBook/media/v4l/v4l2.xml b/Documentation/DocBook/media/v4l/v4l2.xml
> index 0d05e87..06bb179 100644
> --- a/Documentation/DocBook/media/v4l/v4l2.xml
> +++ b/Documentation/DocBook/media/v4l/v4l2.xml
> @@ -462,6 +462,7 @@ and discussions on the V4L mailing list.</revremark>
>      &sub-close;
>      &sub-ioctl;
>      <!-- All ioctls go here. -->
> +    &sub-create-bufs;
>      &sub-cropcap;
>      &sub-dbg-g-chip-ident;
>      &sub-dbg-g-register;
> @@ -504,6 +505,7 @@ and discussions on the V4L mailing list.</revremark>
>      &sub-queryctrl;
>      &sub-query-dv-preset;
>      &sub-querystd;
> +    &sub-prepare-buf;
>      &sub-reqbufs;
>      &sub-s-hw-freq-seek;
>      &sub-streamon;
> diff --git a/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml b/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml
> new file mode 100644
> index 0000000..5f0158c
> --- /dev/null
> +++ b/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml
> @@ -0,0 +1,152 @@
> +<refentry id="vidioc-create-bufs">
> +  <refmeta>
> +    <refentrytitle>ioctl VIDIOC_CREATE_BUFS</refentrytitle>
> +    &manvol;
> +  </refmeta>
> +
> +  <refnamediv>
> +    <refname>VIDIOC_CREATE_BUFS</refname>
> +    <refpurpose>Create buffers for Memory Mapped or User Pointer I/O</refpurpose>
> +  </refnamediv>
> +
> +  <refsynopsisdiv>
> +    <funcsynopsis>
> +      <funcprototype>
> +	<funcdef>int <function>ioctl</function></funcdef>
> +	<paramdef>int <parameter>fd</parameter></paramdef>
> +	<paramdef>int <parameter>request</parameter></paramdef>
> +	<paramdef>struct v4l2_create_buffers *<parameter>argp</parameter></paramdef>
> +      </funcprototype>
> +    </funcsynopsis>
> +  </refsynopsisdiv>
> +
> +  <refsect1>
> +    <title>Arguments</title>
> +
> +    <variablelist>
> +      <varlistentry>
> +	<term><parameter>fd</parameter></term>
> +	<listitem>
> +	  <para>&fd;</para>
> +	</listitem>
> +      </varlistentry>
> +      <varlistentry>
> +	<term><parameter>request</parameter></term>
> +	<listitem>
> +	  <para>VIDIOC_CREATE_BUFS</para>
> +	</listitem>
> +      </varlistentry>
> +      <varlistentry>
> +	<term><parameter>argp</parameter></term>
> +	<listitem>
> +	  <para></para>
> +	</listitem>
> +      </varlistentry>
> +    </variablelist>
> +  </refsect1>
> +
> +  <refsect1>
> +    <title>Description</title>
> +
> +    <para>This ioctl is used to create buffers for <link linkend="mmap">memory
> +mapped</link> or <link linkend="userp">user pointer</link>
> +I/O. It can be used as an alternative 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>To allocate device buffers applications initialize all
> +fields of the <structname>v4l2_create_buffers</structname> structure.
> +They set the <structfield>type</structfield> field in the
> +<structname>v4l2_format</structname> 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. Applications have two possibilities to specify the size of buffers
> +to be prepared: they can either set the <structfield>size</structfield>
> +field explicitly to a non-zero value, or fill in the frame format data in the
> +<structfield>format</structfield> field. In the latter case buffer sizes
> +will be calculated automatically by the driver. 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
> +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.
> +<structfield>count</structfield> can be smaller than the number requested.
> +-ENOMEM is returned, if the driver runs out of free memory.</para>

No need to mention -ENOMEM here. It's already in the return values below;
the same goes for the EINVAL just below.

> +    <para>When the I/O method is not supported the ioctl
> +returns an &EINVAL;.</para>
> +
> +    <table pgwide="1" frame="none" id="v4l2-create-buffers">
> +      <title>struct <structname>v4l2_create_buffers</structname></title>
> +      <tgroup cols="3">
> +	&cs-str;
> +	<tbody valign="top">
> +	  <row>
> +	    <entry>__u32</entry>
> +	    <entry><structfield>index</structfield></entry>
> +	    <entry>The starting buffer index, returned by the driver.</entry>
> +	  </row>
> +	  <row>
> +	    <entry>__u32</entry>
> +	    <entry><structfield>count</structfield></entry>
> +	    <entry>The number of buffers requested or granted.</entry>
> +	  </row>
> +	  <row>
> +	    <entry>&v4l2-memory;</entry>
> +	    <entry><structfield>memory</structfield></entry>
> +	    <entry>Applications set this field to
> +<constant>V4L2_MEMORY_MMAP</constant> or
> +<constant>V4L2_MEMORY_USERPTR</constant>.</entry>
> +	  </row>
> +	  <row>
> +	    <entry>__u32</entry>
> +	    <entry><structfield>size</structfield></entry>
> +	    <entry>Explicit size of buffers, being created.</entry>
> +	  </row>
> +	  <row>
> +	    <entry>&v4l2-format;</entry>
> +	    <entry><structfield>format</structfield></entry>
> +	    <entry>Application has to set the <structfield>type</structfield>
> +field, other fields should be used, if the application wants to allocate buffers
> +for a specific frame format.</entry>
> +	  </row>
> +	  <row>
> +	    <entry>__u32</entry>
> +	    <entry><structfield>reserved</structfield>[8]</entry>
> +	    <entry>A place holder for future extensions.</entry>
> +	  </row>
> +	</tbody>
> +      </tgroup>
> +    </table>
> +  </refsect1>
> +
> +  <refsect1>
> +    &return-value;
> +
> +    <variablelist>
> +      <varlistentry>
> +	<term><errorcode>ENOMEM</errorcode></term>
> +	<listitem>
> +	  <para>No memory to allocate buffers for <link linkend="mmap">memory
> +mapped</link> I/O.</para>
> +	</listitem>
> +      </varlistentry>
> +      <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>
> +	</listitem>
> +      </varlistentry>
> +    </variablelist>
> +  </refsect1>
> +</refentry>
> +
> +<!--
> +Local Variables:
> +mode: sgml
> +sgml-parent-document: "v4l2.sgml"
> +indent-tabs-mode: nil
> +End:
> +-->
> diff --git a/Documentation/DocBook/media/v4l/vidioc-prepare-buf.xml b/Documentation/DocBook/media/v4l/vidioc-prepare-buf.xml
> new file mode 100644
> index 0000000..509e752
> --- /dev/null
> +++ b/Documentation/DocBook/media/v4l/vidioc-prepare-buf.xml
> @@ -0,0 +1,96 @@
> +<refentry id="vidioc-prepare-buf">
> +  <refmeta>
> +    <refentrytitle>ioctl VIDIOC_PREPARE_BUF</refentrytitle>
> +    &manvol;
> +  </refmeta>
> +
> +  <refnamediv>
> +    <refname>VIDIOC_PREPARE_BUF</refname>
> +    <refpurpose>Prepare a buffer for I/O</refpurpose>
> +  </refnamediv>
> +
> +  <refsynopsisdiv>
> +    <funcsynopsis>
> +      <funcprototype>
> +	<funcdef>int <function>ioctl</function></funcdef>
> +	<paramdef>int <parameter>fd</parameter></paramdef>
> +	<paramdef>int <parameter>request</parameter></paramdef>
> +	<paramdef>struct v4l2_buffer *<parameter>argp</parameter></paramdef>

I'm not sure if we want to use struct v4l2_buffer here. It's an obvious
choice, but there's an issue in using it.

The struct is almost full i.e. there are very few reserved fields in it,
namely two, counting the input field which was unused AFAIR. There are now
three ioctls using it as their argument.

Future functionality which would be nice:

- Format counters. Every format set by S_FMT (or gotten by G_FMT) should
  come with a counter value so that the user would know the format of
  dequeued buffers when setting the format on-the-fly. Currently there are
  only bytesperline and length, but the format can't be explicitly
  determined from those.

- Binding to generic DMA buffers. This can likely be achieved by using the m
  union in struct v4l2_buffer. (Speaking of which: these buffers likely have
  a cache behaviour defined for them, e.g. they might be non-cacheable. This
  probably has no effect on the cache flags in V4L2 but it might still be
  good to keep this in mind.)

I don't have an obvious replacement for it either. There are two options I
can see: Create a new struct v4l2_ext_buffer which contains the old
v4l2_buffer plus a bunch of reserved fields, or use the two last fields to
hold a pointer to an extension struct, v4l2_buffer_ext. The new structure
would later be used to contain the reserved fields.

I admit that this is not an issue right now, myt point is that I don't want
this to be an issue in the future either.

> +      </funcprototype>
> +    </funcsynopsis>
> +  </refsynopsisdiv>
> +
> +  <refsect1>
> +    <title>Arguments</title>
> +
> +    <variablelist>
> +      <varlistentry>
> +	<term><parameter>fd</parameter></term>
> +	<listitem>
> +	  <para>&fd;</para>
> +	</listitem>
> +      </varlistentry>
> +      <varlistentry>
> +	<term><parameter>request</parameter></term>
> +	<listitem>
> +	  <para>VIDIOC_PREPARE_BUF</para>
> +	</listitem>
> +      </varlistentry>
> +      <varlistentry>
> +	<term><parameter>argp</parameter></term>
> +	<listitem>
> +	  <para></para>
> +	</listitem>
> +      </varlistentry>
> +    </variablelist>
> +  </refsect1>
> +
> +  <refsect1>
> +    <title>Description</title>
> +
> +    <para>Applications can optionally call the
> +<constant>VIDIOC_PREPARE_BUF</constant> ioctl to pass ownership of the buffer
> +to the driver before actually enqueuing it, using the
> +<constant>VIDIOC_QBUF</constant> ioctl, and to prepare it for future I/O.
> +Such preparations may include cache invalidation or cleaning. Performing them
> +in advance saves time during the actual I/O. In case such cache operations are
> +not required, the application can use one of
> +<constant>V4L2_BUF_FLAG_NO_CACHE_INVALIDATE</constant> and
> +<constant>V4L2_BUF_FLAG_NO_CACHE_CLEAN</constant> flags to skip the respective
> +step.</para>
> +
> +    <para>The <structname>v4l2_buffer</structname> structure is
> +specified in <xref linkend="buffer" />.</para>
> +  </refsect1>
> +
> +  <refsect1>
> +    &return-value;
> +
> +    <variablelist>
> +      <varlistentry>
> +	<term><errorcode>EBUSY</errorcode></term>
> +	<listitem>
> +	  <para>File I/O is in progress.</para>
> +	</listitem>
> +      </varlistentry>
> +      <varlistentry>
> +	<term><errorcode>EINVAL</errorcode></term>
> +	<listitem>
> +	  <para>The buffer <structfield>type</structfield> is not
> +supported, or the <structfield>index</structfield> is out of bounds,
> +or no buffers have been allocated yet, or the
> +<structfield>userptr</structfield> or
> +<structfield>length</structfield> are invalid.</para>
> +	</listitem>
> +      </varlistentry>
> +    </variablelist>
> +  </refsect1>
> +</refentry>
> +
> +<!--
> +Local Variables:
> +mode: sgml
> +sgml-parent-document: "v4l2.sgml"
> +indent-tabs-mode: nil
> +End:
> +-->
> diff --git a/drivers/media/video/v4l2-compat-ioctl32.c b/drivers/media/video/v4l2-compat-ioctl32.c
> index 61979b7..4105f69 100644
> --- a/drivers/media/video/v4l2-compat-ioctl32.c
> +++ b/drivers/media/video/v4l2-compat-ioctl32.c
> @@ -159,11 +159,16 @@ struct v4l2_format32 {
>  	} fmt;
>  };
>  
> -static int get_v4l2_format32(struct v4l2_format *kp, struct v4l2_format32 __user *up)
> +struct v4l2_create_buffers32 {
> +	__u32			index;		/* output: buffers index...index + count - 1 have been created */
> +	__u32			count;
> +	enum v4l2_memory        memory;
> +	__u32			size;		/* Explicit size, e.g., for compressed streams */
> +	struct v4l2_format32	format;		/* "type" is used always, the rest if size == 0 */
> +};
> +
> +static int __get_v4l2_format32(struct v4l2_format *kp, struct v4l2_format32 __user *up)
>  {
> -	if (!access_ok(VERIFY_READ, up, sizeof(struct v4l2_format32)) ||
> -			get_user(kp->type, &up->type))
> -			return -EFAULT;
>  	switch (kp->type) {
>  	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
>  	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
> @@ -192,11 +197,24 @@ static int get_v4l2_format32(struct v4l2_format *kp, struct v4l2_format32 __user
>  	}
>  }
>  
> -static int put_v4l2_format32(struct v4l2_format *kp, struct v4l2_format32 __user *up)
> +static int get_v4l2_format32(struct v4l2_format *kp, struct v4l2_format32 __user *up)
> +{
> +	if (!access_ok(VERIFY_READ, up, sizeof(struct v4l2_format32)) ||
> +			get_user(kp->type, &up->type))
> +			return -EFAULT;
> +	return __get_v4l2_format32(kp, up);
> +}
> +
> +static int get_v4l2_create32(struct v4l2_create_buffers *kp, struct v4l2_create_buffers32 __user *up)
> +{
> +	if (!access_ok(VERIFY_READ, up, sizeof(struct v4l2_create_buffers32)) ||
> +	    copy_from_user(kp, up, offsetof(struct v4l2_create_buffers32, format.fmt)))
> +			return -EFAULT;
> +	return __get_v4l2_format32(&kp->format, &up->format);
> +}
> +
> +static int __put_v4l2_format32(struct v4l2_format *kp, struct v4l2_format32 __user *up)
>  {
> -	if (!access_ok(VERIFY_WRITE, up, sizeof(struct v4l2_format32)) ||
> -		put_user(kp->type, &up->type))
> -		return -EFAULT;
>  	switch (kp->type) {
>  	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
>  	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
> @@ -225,6 +243,22 @@ static int put_v4l2_format32(struct v4l2_format *kp, struct v4l2_format32 __user
>  	}
>  }
>  
> +static int put_v4l2_format32(struct v4l2_format *kp, struct v4l2_format32 __user *up)
> +{
> +	if (!access_ok(VERIFY_WRITE, up, sizeof(struct v4l2_format32)) ||
> +		put_user(kp->type, &up->type))
> +		return -EFAULT;
> +	return __put_v4l2_format32(kp, up);
> +}
> +
> +static int put_v4l2_create32(struct v4l2_create_buffers *kp, struct v4l2_create_buffers32 __user *up)
> +{
> +	if (!access_ok(VERIFY_WRITE, up, sizeof(struct v4l2_create_buffers32)) ||
> +	    copy_to_user(up, kp, offsetof(struct v4l2_create_buffers32, format.fmt)))
> +			return -EFAULT;
> +	return __put_v4l2_format32(&kp->format, &up->format);
> +}
> +
>  struct v4l2_standard32 {
>  	__u32		     index;
>  	__u32		     id[2]; /* __u64 would get the alignment wrong */
> @@ -702,6 +736,8 @@ static int put_v4l2_event32(struct v4l2_event *kp, struct v4l2_event32 __user *u
>  #define VIDIOC_S_EXT_CTRLS32    _IOWR('V', 72, struct v4l2_ext_controls32)
>  #define VIDIOC_TRY_EXT_CTRLS32  _IOWR('V', 73, struct v4l2_ext_controls32)
>  #define	VIDIOC_DQEVENT32	_IOR ('V', 89, struct v4l2_event32)
> +#define VIDIOC_CREATE_BUFS32	_IOWR('V', 92, struct v4l2_create_buffers32)
> +#define VIDIOC_PREPARE_BUF32	_IOWR('V', 93, struct v4l2_buffer32)
>  
>  #define VIDIOC_OVERLAY32	_IOW ('V', 14, s32)
>  #define VIDIOC_STREAMON32	_IOW ('V', 18, s32)
> @@ -721,6 +757,7 @@ static long do_video_ioctl(struct file *file, unsigned int cmd, unsigned long ar
>  		struct v4l2_standard v2s;
>  		struct v4l2_ext_controls v2ecs;
>  		struct v4l2_event v2ev;
> +		struct v4l2_create_buffers v2crt;
>  		unsigned long vx;
>  		int vi;
>  	} karg;
> @@ -751,6 +788,8 @@ static long do_video_ioctl(struct file *file, unsigned int cmd, unsigned long ar
>  	case VIDIOC_S_INPUT32: cmd = VIDIOC_S_INPUT; break;
>  	case VIDIOC_G_OUTPUT32: cmd = VIDIOC_G_OUTPUT; break;
>  	case VIDIOC_S_OUTPUT32: cmd = VIDIOC_S_OUTPUT; break;
> +	case VIDIOC_CREATE_BUFS32: cmd = VIDIOC_CREATE_BUFS; break;
> +	case VIDIOC_PREPARE_BUF32: cmd = VIDIOC_PREPARE_BUF; break;
>  	}
>  
>  	switch (cmd) {
> @@ -775,6 +814,12 @@ static long do_video_ioctl(struct file *file, unsigned int cmd, unsigned long ar
>  		compatible_arg = 0;
>  		break;
>  
> +	case VIDIOC_CREATE_BUFS:
> +		err = get_v4l2_create32(&karg.v2crt, up);
> +		compatible_arg = 0;
> +		break;
> +
> +	case VIDIOC_PREPARE_BUF:
>  	case VIDIOC_QUERYBUF:
>  	case VIDIOC_QBUF:
>  	case VIDIOC_DQBUF:
> @@ -860,6 +905,11 @@ static long do_video_ioctl(struct file *file, unsigned int cmd, unsigned long ar
>  		err = put_v4l2_format32(&karg.v2f, up);
>  		break;
>  
> +	case VIDIOC_CREATE_BUFS:
> +		err = put_v4l2_create32(&karg.v2crt, up);
> +		break;
> +
> +	case VIDIOC_PREPARE_BUF:
>  	case VIDIOC_QUERYBUF:
>  	case VIDIOC_QBUF:
>  	case VIDIOC_DQBUF:
> @@ -959,6 +1009,8 @@ long v4l2_compat_ioctl32(struct file *file, unsigned int cmd, unsigned long arg)
>  	case VIDIOC_DQEVENT32:
>  	case VIDIOC_SUBSCRIBE_EVENT:
>  	case VIDIOC_UNSUBSCRIBE_EVENT:
> +	case VIDIOC_CREATE_BUFS32:
> +	case VIDIOC_PREPARE_BUF32:
>  		ret = do_video_ioctl(file, cmd, arg);
>  		break;
>  
> diff --git a/drivers/media/video/v4l2-ioctl.c b/drivers/media/video/v4l2-ioctl.c
> index 002ce13..7824152 100644
> --- a/drivers/media/video/v4l2-ioctl.c
> +++ b/drivers/media/video/v4l2-ioctl.c
> @@ -260,6 +260,8 @@ static const char *v4l2_ioctls[] = {
>  	[_IOC_NR(VIDIOC_DQEVENT)]	   = "VIDIOC_DQEVENT",
>  	[_IOC_NR(VIDIOC_SUBSCRIBE_EVENT)]  = "VIDIOC_SUBSCRIBE_EVENT",
>  	[_IOC_NR(VIDIOC_UNSUBSCRIBE_EVENT)] = "VIDIOC_UNSUBSCRIBE_EVENT",
> +	[_IOC_NR(VIDIOC_CREATE_BUFS)]      = "VIDIOC_CREATE_BUFS",
> +	[_IOC_NR(VIDIOC_PREPARE_BUF)]      = "VIDIOC_PREPARE_BUF",
>  };
>  #define V4L2_IOCTLS ARRAY_SIZE(v4l2_ioctls)
>  
> @@ -2216,6 +2218,36 @@ static long __video_do_ioctl(struct file *file,
>  		dbgarg(cmd, "type=0x%8.8x", sub->type);
>  		break;
>  	}
> +	case VIDIOC_CREATE_BUFS:
> +	{
> +		struct v4l2_create_buffers *create = arg;
> +
> +		if (!ops->vidioc_create_bufs)
> +			break;
> +		ret = check_fmt(ops, create->format.type);
> +		if (ret)
> +			break;
> +
> +		if (create->size)
> +			CLEAR_AFTER_FIELD(create, count);
> +		ret = ops->vidioc_create_bufs(file, fh, create);
> +
> +		dbgarg(cmd, "count=%d\n", create->count);
> +		break;
> +	}
> +	case VIDIOC_PREPARE_BUF:
> +	{
> +		struct v4l2_buffer *b = arg;
> +
> +		if (!ops->vidioc_prepare_buf)
> +			break;
> +
> +		ret = ops->vidioc_prepare_buf(file, fh, b);
> +
> +		dbgarg(cmd, "index=%d", b->index);
> +		break;
> +	}
>  	default:
>  	{
>  		bool valid_prio = true;
> diff --git a/include/linux/videodev2.h b/include/linux/videodev2.h
> index fca24cc..0b594c7 100644
> --- a/include/linux/videodev2.h
> +++ b/include/linux/videodev2.h
> @@ -653,6 +653,9 @@ struct v4l2_buffer {
>  #define V4L2_BUF_FLAG_ERROR	0x0040
>  #define V4L2_BUF_FLAG_TIMECODE	0x0100	/* timecode field is valid */
>  #define V4L2_BUF_FLAG_INPUT     0x0200  /* input field is valid */
> +/* Cache handling flags */
> +#define V4L2_BUF_FLAG_NO_CACHE_INVALIDATE	0x0400
> +#define V4L2_BUF_FLAG_NO_CACHE_CLEAN		0x0800
>  
>  /*
>   *	O V E R L A Y   P R E V I E W
> @@ -2092,6 +2095,16 @@ struct v4l2_dbg_chip_ident {
>  	__u32 revision;    /* chip revision, chip specific */
>  } __attribute__ ((packed));
>  
> +/* VIDIOC_CREATE_BUFS */
> +struct v4l2_create_buffers {
> +	__u32			index;		/* output: buffers index...index + count - 1 have been created */
> +	__u32			count;
> +	enum v4l2_memory        memory;

Aren't enums something to avoid in public APIs? -> __u32?

> +	__u32			size;		/* Explicit size, e.g., for compressed streams */
> +	struct v4l2_format	format;		/* "type" is used always, the rest if size == 0 */
> +	__u32			reserved[8];
> +};
> +
>  /*
>   *	I O C T L   C O D E S   F O R   V I D E O   D E V I C E S
>   *
> @@ -2182,6 +2195,9 @@ struct v4l2_dbg_chip_ident {
>  #define	VIDIOC_SUBSCRIBE_EVENT	 _IOW('V', 90, struct v4l2_event_subscription)
>  #define	VIDIOC_UNSUBSCRIBE_EVENT _IOW('V', 91, struct v4l2_event_subscription)
>  
> +#define VIDIOC_CREATE_BUFS	_IOWR('V', 92, struct v4l2_create_buffers)
> +#define VIDIOC_PREPARE_BUF	 _IOW('V', 93, struct v4l2_buffer)
> +
>  /* Reminder: when adding new ioctls please add support for them to
>     drivers/media/video/v4l2-compat-ioctl32.c as well! */
>  
> diff --git a/include/media/v4l2-ioctl.h b/include/media/v4l2-ioctl.h
> index dd9f1e7..4d1c74a 100644
> --- a/include/media/v4l2-ioctl.h
> +++ b/include/media/v4l2-ioctl.h
> @@ -122,6 +122,8 @@ struct v4l2_ioctl_ops {
>  	int (*vidioc_qbuf)    (struct file *file, void *fh, struct v4l2_buffer *b);
>  	int (*vidioc_dqbuf)   (struct file *file, void *fh, struct v4l2_buffer *b);
>  
> +	int (*vidioc_create_bufs)(struct file *file, void *fh, struct v4l2_create_buffers *b);
> +	int (*vidioc_prepare_buf)(struct file *file, void *fh, struct v4l2_buffer *b);
>  
>  	int (*vidioc_overlay) (struct file *file, void *fh, unsigned int i);
>  	int (*vidioc_g_fbuf)   (struct file *file, void *fh,
> -- 
> 1.7.2.5
> 

Regards,

-- 
Sakari Ailus
sakari.ailus@iki.fi