Hi Sakari,
Thank you for the review.
On Thursday 21 Apr 2016 11:44:26 Sakari Ailus wrote:
> On Thu, Apr 21, 2016 at 03:40:26AM +0300, 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+rene...@ideasonboard.com>
> > ---
> >
> > 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>
>
> I propose:
>
> s/-/ /
How about metadata ? That's the spelling used by wikipedia
> > +
> > + <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.
>
> Ditto.
>
> > + </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.
>
> Where does 255 come from? At least in kernel the minor number space has got
> 20 bits, not 8. Not that I prefer having that many meta data nodes, but
> still that's a possibility.
We have
#define VIDEO_NUM_DEVICES 256
in drivers/media/v4l2-core/v4l2-dev.c. If you want to take care of the code
I'll update the documentation :-)
> > + </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
> > +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
> > +<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>
>
> 200 bytes is reserved for this struct in all IOCTLs. How about using closer
> to that amount? 24 bytes of reserved space isn't much. Albeit you could
> argue that this struct could be changed later on as it does not affect IOCTL
> argument size.
Should we just get rid of the reserved field then ?
> > + </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.
> > + </para>
> > +
> > + </section>
[snip]
> > diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> > b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c index
> > bacecbd68a6d..da2d836e8887 100644
> > --- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> > +++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> > @@ -161,6 +161,20 @@ static inline int put_v4l2_sdr_format(struct
> > v4l2_sdr_format *kp, struct v4l2_sd>
> > return 0;
> >
> > }
> >
> > +static inline int get_v4l2_meta_format(struct v4l2_meta_format *kp,
> > struct v4l2_meta_format __user *up)
>
> I think I'd wrap this. Same below.
I've followed the existing coding style of the file, I'm fine with wrapping
the lines if you think that's better.
> > +{
> > + if (copy_from_user(kp, up, sizeof(struct v4l2_meta_format)))
> > + return -EFAULT;
> > + return 0;
> > +}
> > +
> > +static inline int put_v4l2_meta_format(struct v4l2_meta_format *kp,
> > struct v4l2_meta_format __user *up) +{
> > + if (copy_to_user(up, kp, sizeof(struct v4l2_meta_format)))
> > + return -EFAULT;
> > + return 0;
> > +}
> > +
> > struct v4l2_format32 {
> > __u32 type; /* enum v4l2_buf_type */
> > union {
[snip]
> > diff --git a/include/uapi/linux/videodev2.h
> > b/include/uapi/linux/videodev2.h index e895975c5b0e..5035295a0138 100644
> > --- a/include/uapi/linux/videodev2.h
> > +++ b/include/uapi/linux/videodev2.h
[snip]
> > @@ -2007,6 +2009,17 @@ struct v4l2_sdr_format {
> > } __attribute__ ((packed));
> >
> > /**
> > + * struct v4l2_meta_format - meta-data format definition
>
> An empty line here would be nice.
The kerneldoc style doesn't add an empty line after the first, and the
kerneldoc blocks in this file don't either.
> > + * @pixelformat: little endian four character code (fourcc)
> > + * @buffersize: maximum size in bytes required for data
> > + */
> > +struct v4l2_meta_format {
> > + __u32 pixelformat;
> > + __u32 buffersize;
> > + __u8 reserved[24];
> > +} __attribute__ ((packed));
> > +
> > +/**
> > * struct v4l2_format - stream data format
> > * @type: enum v4l2_buf_type; type of the data stream
> > * @pix: definition of an image format
[snip]
--
Regards,
Laurent Pinchart
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