On Friday 06 August 2010 22:21:36 Guennadi Liakhovetski wrote:
> On Fri, 6 Aug 2010, Laurent Pinchart wrote:
>
> > Hi Guennadi,
> >
> > On Thursday 05 August 2010 20:03:46 Guennadi Liakhovetski wrote:
> > > Many video drivers implement a discrete set of frame formats and thus face
> > > a task of finding the best match for a user-requested format. Implementing
> > > this in a generic function has also an advantage, that different drivers
> > > with similar supported format sets will select the same format for the
> > > user, which improves consistency across drivers.
> > >
> > > Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@xxxxxx>
> > > ---
> > >
> > > I'm currently away from my hardware, so, this is only compile tested and
> > > run-time tested with a test application. In any case, reviews and
> > > suggestions welcome.
> > >
> > > drivers/media/video/v4l2-common.c | 26 ++++++++++++++++++++++++++
> > > include/linux/videodev2.h | 10 ++++++++++
> > > 2 files changed, 36 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/drivers/media/video/v4l2-common.c
> > > b/drivers/media/video/v4l2-common.c index 4e53b0b..90727e6 100644
> > > --- a/drivers/media/video/v4l2-common.c
> > > +++ b/drivers/media/video/v4l2-common.c
> > > @@ -1144,3 +1144,29 @@ int v4l_fill_dv_preset_info(u32 preset, struct
> > > v4l2_dv_enum_preset *info) return 0;
> > > }
> > > EXPORT_SYMBOL_GPL(v4l_fill_dv_preset_info);
> > > +
> > > +struct v4l2_frmsize_discrete *v4l2_find_nearest_format(struct
> > > v4l2_discrete_probe *probe, + s32 width, s32 height)
> > > +{
> > > + int i;
> > > + u32 error, min_error = ~0;
> > > + struct v4l2_frmsize_discrete *size, *best = NULL;
> > > +
> > > + if (!probe)
> > > + return best;
> > > +
> > > + for (i = 0, size = probe->sizes; i < probe->num_sizes; i++, size++) {
> > > + if (probe->probe && !probe->probe(probe))
> >
> > What's this call for ?
>
> Well, atm, I don't think I have a specific case right now, but I think, it
> can well be the case, that not all frame sizes are always usable in the
> driver, depending on other circumstances. E.g., depending on the pixel /
> fourcc code. So, in this case the driver just provides a probe method to
> filter out inapplicable sizes.
Never add code just because you think it might be needed in the future. Especially
not for kernel internal code that you can change anyway if needed.
In this case you just want to give a simple const array with width and height
pairs ending at 0, 0 or pass in the length of the array, whatever you prefer,
and return the array index for the closest match.
Keep it simple.
Regards,
Hans
>
> Thanks
> Guennadi
>
> >
> > > + continue;
> > > + error = abs(size->width - width) + abs(size->height - height);
> > > + if (error < min_error) {
> > > + min_error = error;
> > > + best = size;
> > > + }
> > > + if (!error)
> > > + break;
> > > + }
> > > +
> > > + return best;
> > > +}
> > > +EXPORT_SYMBOL_GPL(v4l2_find_nearest_format);
> > > diff --git a/include/linux/videodev2.h b/include/linux/videodev2.h
> > > index 047f7e6..f622bba 100644
> > > --- a/include/linux/videodev2.h
> > > +++ b/include/linux/videodev2.h
> > > @@ -394,6 +394,16 @@ struct v4l2_frmsize_discrete {
> > > __u32 height; /* Frame height [pixel] */
> > > };
> > >
> > > +struct v4l2_discrete_probe {
> > > + struct v4l2_frmsize_discrete *sizes;
> > > + int num_sizes;
> > > + void *priv;
> > > + bool (*probe)(struct v4l2_discrete_probe *);
> > > +};
> > > +
> > > +struct v4l2_frmsize_discrete *v4l2_find_nearest_format(struct
> > > v4l2_discrete_probe *probe, + s32 width, s32 height);
> > > +
> > > struct v4l2_frmsize_stepwise {
> > > __u32 min_width; /* Minimum frame width [pixel] */
> > > __u32 max_width; /* Maximum frame width [pixel] */
> >
>
> ---
> Guennadi Liakhovetski, Ph.D.
> Freelance Open-Source Software Developer
> http://www.open-technology.de/
>
--
Hans Verkuil - video4linux developer - sponsored by TANDBERG, part of Cisco
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