Hi Hans, Thank you for the review. On Monday 23 May 2016 12:09:16 Hans Verkuil wrote: > On 05/12/2016 02:18 AM, Laurent Pinchart wrote: > > The metadata buffer type is used to transfer metadata between userspace > > and kernelspace through a V4L2 buffers queue. It comes with a new > > metadata capture capability and format description. > > Thanks for the patch! I have some comments/suggestions below: > > Signed-off-by: Laurent Pinchart > > <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx> > > --- > > > > Documentation/DocBook/media/v4l/dev-meta.xml | 93 ++++++++++++++++++++++ > > Documentation/DocBook/media/v4l/v4l2.xml | 1 + > > drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 19 ++++++ > > drivers/media/v4l2-core/v4l2-dev.c | 16 +++-- > > drivers/media/v4l2-core/v4l2-ioctl.c | 34 ++++++++++ > > drivers/media/v4l2-core/videobuf2-v4l2.c | 3 + > > include/media/v4l2-ioctl.h | 8 +++ > > include/uapi/linux/videodev2.h | 14 ++++ > > 8 files changed, 182 insertions(+), 6 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..9b5b1fba2007 > > --- /dev/null > > +++ b/Documentation/DocBook/media/v4l/dev-meta.xml > > @@ -0,0 +1,93 @@ > > + <title>Metadata Interface</title> > > + > > + <note> > > + <title>Experimental</title> > > + <para>This is an <link linkend="experimental"> experimental </link> > > No space before/after 'experimental'. It will look ugly in the docbook (I > tried it :-) ). Will be fixed in the next version. > > + interface and may change in the future.</para> > > + </note> > > + > > + <para> > > +Metadata 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 metadata to userspace and control > > +of that operation. > > I think it can also be in the other direction. I'm thinking of metadata > needed by codecs. I'm not sure if it should be mentioned that this is not > supported at the moment and that the ML should be contacted for more info > if someone wants this. Metadata for codecs make sense, but given that the topic hasn't been researched yet, I've kept metadata support focused on the capture side only for now. I propose revisiting the topic if (or rather when) someone needs metadata support on output video nodes. > > + </para> > > + > > + <para> > > +The metadata interface is implemented on video capture devices. The > > device can > > s/on/for/? I meant "on video capture device nodes", I'll fix that. > > +be dedicated to metadata or can implement both video and metadata capture > > +as specified in its reported capabilities. > > + </para> > > + > > + <section> > > + <title>Querying Capabilities</title> > > + > > + <para> > > +Devices supporting the metadata 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 metadata to memory. > > + </para> > > I know this is a copy and paste from the other interface descriptions, but > it is rather outdated. I would write this instead: > > <para> > Device nodes supporting the metadata interface set the > <constant>V4L2_CAP_META_CAPTURE</constant> flag in the > <structfield>device_caps</structfield> field of &v4l2-capability; > returned by the &VIDIOC-QUERYCAP; ioctl. That flag means the device node can > capture metadata to memory. > </para> Will be fixed in the next version. > Any driver using this will be recent and always have a valid device_caps > field (which, as you know, didn't exist in old kernels). > > I find the capabilities field fairly useless in most cases due to the fact > that it contains the capabilities of all device nodes created by the device > driver. I agree. > > + <para> > > +At least one of the read/write or streaming I/O methods must be > > supported. > > + </para> > > + </section> > > + > > + <section> > > + <title>Data Format Negotiation</title> > > + > > + <para> > > +The metadata device uses the <link linkend="format">format</link> ioctls > > to +select the capture format. The metadata 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>dataformat</structfield> and > > +<structfield>buffersize</structfield>, of struct &v4l2-meta-format; that > > are +used. Content of the <structfield>dataformat</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. > > Should it be mentioned here that changing the video format might change the > buffersize? In case the buffersize is always a multiple of the width? I'll reply to Sakari's mail further down in this thread about this. > > + </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>dataformat</structfield></entry> > > + <entry> > > +The data format, set by the application. This is a little endian > > +<link linkend="v4l2-fourcc">four character code</link>. > > +V4L2 defines metadata 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> > > + > > + </section> [snip] > > diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c > > b/drivers/media/v4l2-core/v4l2-ioctl.c index 28e5be2c2eef..5d003152ff68 > > 100644 > > --- a/drivers/media/v4l2-core/v4l2-ioctl.c > > +++ b/drivers/media/v4l2-core/v4l2-ioctl.c [snip] > > @@ -1534,6 +1558,11 @@ static int v4l_s_fmt(const struct v4l2_ioctl_ops > > *ops, > > break; > > CLEAR_AFTER_FIELD(p, fmt.sdr); > > return ops->vidioc_s_fmt_sdr_out(file, fh, arg); > > + case V4L2_BUF_TYPE_META_CAPTURE: > > + if (unlikely(!is_rx || !is_vid || > > !ops->vidioc_s_fmt_meta_cap)) > > + break; > > + CLEAR_AFTER_FIELD(p, fmt.meta); > > I would suggest using "CLEAR_FROM_FIELD(p, fmt.meta.reserved)" here. Of > course, you'd need to add a new CLEAR_FROM_FIELD macro for this. > > I think this also should be used for the SDR_CAPTURE/OUTPUT types and > possibly for other types as well (can be done later of course). > > This would also zero the reserved field, so drivers don't need to care about > it. Will be fixed in the next version (in v4l_g_fmt() too). > > + return ops->vidioc_s_fmt_meta_cap(file, fh, arg); > > } > > return -EINVAL; > > } -- Regards, Laurent Pinchart
