On 04/22/2016 03:58 PM, Mauro Carvalho Chehab wrote:
> Em Fri, 22 Apr 2016 09:46:04 +0200
> Hans Verkuil <hverkuil@xxxxxxxxx> escreveu:
>
>> 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.
>
> metaformat is OK.
>
>>
>>>
>>>>> +<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).
>
> Agreed.
>
>>>
>>>>> + </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.
>
> It actually makes sense to put statistics as an example of such
> metadata, as this is the main(and currently only) usage for this
> devnode.
Then I would say 'like statistics' here. But I still don't like this to be
honest. Heck, Nick Dyer posted a patch series for getting diagnostics yesterday,
which would be a good fit as well.
Anyway, it's not worth a long discussion :-)
Regards,
Hans
--
To unsubscribe from this list: send the line "unsubscribe linux-media" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
