On 04/21/2016 09:15 PM, Laurent Pinchart wrote:
> Hi Hans,
>
> Thank you for the review.
>
> On Thursday 21 Apr 2016 08:39:59 Hans Verkuil wrote:
>> Hi Laurent,
>>
>> Thanks for the patch!
>>
>> Some, mostly small, comments follow:
>>
>> On 04/21/2016 02:40 AM, Laurent Pinchart wrote:
>>> The meta-data video device is used to transfer meta-data between
>>> userspace and kernelspace through a V4L2 buffers queue. It comes with a
>>> new meta-data capture capability, buffer type and format description.
>>>
>>> Signed-off-by: Laurent Pinchart
>>> <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx>
>>> ---
>>>
>>> Documentation/DocBook/media/v4l/dev-meta.xml | 100 +++++++++++++++++++++
>>> Documentation/DocBook/media/v4l/v4l2.xml | 1 +
>>> drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 19 +++++
>>> drivers/media/v4l2-core/v4l2-dev.c | 21 +++++-
>>> drivers/media/v4l2-core/v4l2-ioctl.c | 39 ++++++++++
>>> drivers/media/v4l2-core/videobuf2-v4l2.c | 3 +
>>> include/media/v4l2-dev.h | 3 +-
>>> include/media/v4l2-ioctl.h | 8 +++
>>> include/uapi/linux/media.h | 2 +
>>> include/uapi/linux/videodev2.h | 14 ++++
>>> 10 files changed, 208 insertions(+), 2 deletions(-)
>>> create mode 100644 Documentation/DocBook/media/v4l/dev-meta.xml
>>>
>>> diff --git a/Documentation/DocBook/media/v4l/dev-meta.xml
>>> b/Documentation/DocBook/media/v4l/dev-meta.xml new file mode 100644
>>> index 000000000000..ddc685186015
>>> --- /dev/null
>>> +++ b/Documentation/DocBook/media/v4l/dev-meta.xml
>>> @@ -0,0 +1,100 @@
>>> + <title>Meta-Data Interface</title>
>>> +
>>> + <note>
>>> + <title>Experimental</title>
>>> + <para>This is an <link linkend="experimental"> experimental </link>
>>> + interface and may change in the future.</para>
>>> + </note>
>>> +
>>> + <para>
>>> +Meta-data refers to any non-image data that supplements video frames with
>>> +additional information. This may include statistics computed over the
>>> image +or frame capture parameters supplied by the image source. This
>>> interface is +intended for transfer of meta-data to userspace and control
>>> of that operation. + </para>
>>> +
>>> + <para>
>>> +Meta-data devices are accessed through character device special files
>>> named +<filename>/dev/v4l-meta0</filename> to
>>> <filename>/dev/v4l-meta255</filename> +with major number 81 and
>>> dynamically allocated minor numbers 0 to 255. + </para>
>>> +
>>> + <section>
>>> + <title>Querying Capabilities</title>
>>> +
>>> + <para>
>>> +Devices supporting the meta-data interface set the
>>> +<constant>V4L2_CAP_META_CAPTURE</constant> flag in the
>>> +<structfield>capabilities</structfield> field of &v4l2-capability;
>>> +returned by the &VIDIOC-QUERYCAP; ioctl. That flag means the device can
>>> capture +meta-data to memory.
>>> + </para>
>>> + <para>
>>> +At least one of the read/write, streaming or asynchronous I/O methods
>>> must
>>
>> I think we can drop 'asynchronous I/O' since that's never been used. I
>> assume this is copy-and-pasted and we should probably just remove any
>> reference to async IO.
>
> Agreed. I'll fix it.
>
>>> +be supported.
>>> + </para>
>>> + </section>
>>> +
>>> + <section>
>>> + <title>Data Format Negotiation</title>
>>> +
>>> + <para>
>>> +The meta-data device uses the <link linkend="format">format</link> ioctls
>>> to +select the capture format. The meta-data buffer content format is
>>> bound to that +selectable format. In addition to the basic
>>> +<link linkend="format">format</link> ioctls, the &VIDIOC-ENUM-FMT; ioctl
>>> +must be supported as well.
>>> + </para>
>>> +
>>> + <para>
>>> +To use the <link linkend="format">format</link> ioctls applications set
>>> the +<structfield>type</structfield> field of a &v4l2-format; to
>>> +<constant>V4L2_BUF_TYPE_META_CAPTURE</constant> and use the
>>> &v4l2-meta-format; +<structfield>meta</structfield> member of the
>>> <structfield>fmt</structfield> +union as needed per the desired
>>> operation.
>>> +Currently there are two fields, <structfield>pixelformat</structfield>
>>> and
>>
>> Shouldn't that be metaformat? Since there are no pixels here? It was a bit
>> dubious to call it pixelformat for SDR as well, but at least there you
>> still have discrete samples which might be called pixels with some
>> imagination. But certainly doesn't apply to meta data.
>
> How about dataformat ? Or just format ?
Since the fourcc defines are called V4L2_META_FMT_ I think metaformat is a
good name. It's consistent with the other meta-related namings.
>
>>> +<structfield>buffersize</structfield>, of struct &v4l2-meta-format; that
>>> are +used. Content of the <structfield>pixelformat</structfield> is the
>>> V4L2 FourCC +code of the data format. The
>>> <structfield>buffersize</structfield> field is the +maximum buffer size
>>> in bytes required for data transfer, set by the driver in +order to
>>> inform applications.
>>> + </para>
>>> +
>>> + <table pgwide="1" frame="none" id="v4l2-meta-format">
>>> + <title>struct <structname>v4l2_meta_format</structname></title>
>>> + <tgroup cols="3">
>>> + &cs-str;
>>> + <tbody valign="top">
>>> + <row>
>>> + <entry>__u32</entry>
>>> + <entry><structfield>pixelformat</structfield></entry>
>>> + <entry>
>>> +The data format or type of compression, set by the application. This is a
>>> +little endian <link linkend="v4l2-fourcc">four character code</link>.
>>> +V4L2 defines meta-data formats in <xref linkend="meta-formats" />.
>>> + </entry>
>>> + </row>
>>> + <row>
>>> + <entry>__u32</entry>
>>> + <entry><structfield>buffersize</structfield></entry>
>>> + <entry>
>>> +Maximum size in bytes required for data. Value is set by the driver.
>>> + </entry>
>>> + </row>
>>> + <row>
>>> + <entry>__u8</entry>
>>> + <entry><structfield>reserved[24]</structfield></entry>
>>> + <entry>This array is reserved for future extensions.
>>> +Drivers and applications must set it to zero.</entry>
>>> + </row>
>>> + </tbody>
>>> + </tgroup>
>>> + </table>
>>> +
>>> + <para>
>>> +A meta-data device may support <link linkend="rw">read/write</link>
>>> +and/or streaming (<link linkend="mmap">memory mapping</link>
>>> +or <link linkend="userp">user pointer</link>) I/O.
>>
>> Add dma-buf to this as well, or just say "streaming I/O" without listing
>> the possibilities. If this is copied-and-pasted, then the same should be
>> done in the original.
>
> How about removing the paragraph completely ? This is already addressed in the
> previous section ("Querying Capabilities").
Let's remove this. I am considering to make a proposal to tighten this up.
I've never been happy with the way stream I/O capabilities are signaled (or
really the lack of any signaling).
>
>>> + </para>
>>> +
>>> + </section>
>
> [snip]
>
>>> diff --git a/drivers/media/v4l2-core/v4l2-dev.c
>>> b/drivers/media/v4l2-core/v4l2-dev.c index 70b559d7ca80..d8cbf11eae4e
>>> 100644
>>> --- a/drivers/media/v4l2-core/v4l2-dev.c
>>> +++ b/drivers/media/v4l2-core/v4l2-dev.c
>
> [snip]
>
>>> @@ -845,6 +859,8 @@ static int video_register_media_controller(struct
>>> video_device *vdev, int type)>
>>> * %VFL_TYPE_SUBDEV - A subdevice
>>> *
>>> * %VFL_TYPE_SDR - Software Defined Radio
>>>
>>> + *
>>> + * %VFL_TYPE_META - Meta-data (including statistics)
>>
>> I would drop the '(including statistics)' part. It feels weird that
>> 'statistics' are singled out, it makes the reader wonder what is so special
>> about it that it needs to be mentioned explicitly.
>
> Done.
>
>>> */
>>>
>>> int __video_register_device(struct video_device *vdev, int type, int nr,
>>>
>>> int warn_if_nr_in_use, struct module *owner)
>
> [snip]
>
Regards,
Hans
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