Le vendredi 25 mai 2018 à 21:14 -0400, Nicolas Dufresne a écrit :
> Le vendredi 25 mai 2018 à 17:19 -0700, Steve Longerbeam a écrit :
> >
> > On 05/25/2018 05:10 PM, Nicolas Dufresne wrote:
> > > (in text this time, sorry)
> > >
> > > Le vendredi 25 mai 2018 à 16:53 -0700, Steve Longerbeam a écrit :
> > > > Add a macro that returns true if the given field type is
> > > > 'sequential',
> > > > that is, the data is transmitted, or exists in memory, as all top
> > > > field
> > > > lines followed by all bottom field lines, or vice-versa.
> > > >
> > > > Signed-off-by: Steve Longerbeam <steve_longerbeam@xxxxxxxxxx>
> > > > ---
> > > > include/uapi/linux/videodev2.h | 4 ++++
> > > > 1 file changed, 4 insertions(+)
> > > >
> > > > diff --git a/include/uapi/linux/videodev2.h
> > > > b/include/uapi/linux/videodev2.h
> > > > index 600877b..408ee96 100644
> > > > --- a/include/uapi/linux/videodev2.h
> > > > +++ b/include/uapi/linux/videodev2.h
> > > > @@ -126,6 +126,10 @@ enum v4l2_field {
> > > > (field) == V4L2_FIELD_INTERLACED_BT ||\
> > > > (field) == V4L2_FIELD_SEQ_TB ||\
> > > > (field) == V4L2_FIELD_SEQ_BT)
> > > > +#define V4L2_FIELD_IS_SEQUENTIAL(field) \
> > > > + ((field) == V4L2_FIELD_SEQ_TB ||\
> > > > + (field) == V4L2_FIELD_SEQ_BT ||\
> > > > + (field) == V4L2_FIELD_ALTERNATE)
> > >
> > > No, alternate has no place here, in alternate mode each buffers have
> > > only one field.
> >
> > Then I misunderstand what is meant by "alternate". The name implies
> > to me that a source sends top or bottom field alternately, or top/bottom
> > fields exist in memory buffers alternately, but with no information about
> > which field came first. In other words, "alternate" is either seq-tb or
> > seq-bt,
> > without any info about field order.
> >
> > If it is just one field in a memory buffer, why isn't it called
> > V4L2_FIELD_TOP_OR_BOTTOM, e.g. we don't know which?
>
> I don't see why this could be better then ALTERNATE, were buffers are
> only top or bottom fields alternatively. And even if there was another
> possible name, this is public API.
>
> V4L2_FIELD_ALTERNATE is a mode, that will only be used with
> v4l2_pix_format or v4l2_pix_format_mplane. I should never bet set on
> the v4l2_buffer.field, instead the driver indicates the parity of the
> field by setting V42_FIELD_TOP/BOTTOM on the v4l2_buffer returned by
> DQBUF. This is a very different mode of operation compared to
> sequential, hence why I believe it is wrong to make it part of the new
> helper. So far, it's the only field value that has this asymmetric
> usage and meaning.
I should have put some references. The explanation of the modes, with a
temporal representation of the fields. Small note, in ALTERNATE mode
bottom and top fields will likely not share the same timestamp, it is a
mode used to achieve lower latency.
https://linuxtv.org/downloads/v4l-dvb-apis/uapi/v4l/field-order.html#c.v4l2_field
And in this section, you'll see a paragraph that explain the field
values when running in ALTERNATE mode.
https://linuxtv.org/downloads/v4l-dvb-apis/uapi/v4l/buffer.html#c.v4l2_buffer
>
> >
> > Steve
> >
