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V4L2 *STD ioctls with webcam drivers

On Fri, Mar 10, 2006 at 04:19:32PM +0000, Eduardo Pérez Ureta wrote:
> On 2006-03-09 07:23:27 -0300, Mauro Carvalho Chehab wrote:
> > Em Qua, 2006-03-01 às 17:12 +0100, Laurent Pinchart escreveu:
> > > > I would like to know what the correct implementation of the *STD ioctls
> > > > in V4L2 webcam drivers is.
> > > >
> > > > Either they return -EINVAL or they get implemented like the attached
> > > > patch in the http://linux-uvc.berlios.de/ USB driver or like the
> > > > http://www.saillard.org/linux/pwc/ driver.
> > > >
> > > > I'm asking because different USB webcam drivers implement different code
> > > > and I think a consensus should be reached if we want all the
> > > > applications working properly with different drivers.
> > > 
> > > Thanks for raising the issue here, I was planning to send a mail myself but 
> > > I'm unfortunately a bit busy at the moment.
> > > 
> > > As I already stated, my understanding is that the V4L2 spec doesn't make those 
> > > ioctls mandatory. Returning -EINVAL is the proper way to deal with the *STD 
> > > ioctls when they are not supported by the driver.
> > IMHO, returning -EINVAL is the better for non-supported ioctls.
> 
> Could you give your comments on this issue?
> 

It's a good question, some applications are broken and want to set a
standard, some don't test the return value. In the v4l2 API, we can set that
the standard for the webcam is V4L2_STD_UNKNOWN, or better use
V4L2_STD_WEBCAM. Because most developper of applications don't understand
video standard (like me), i prefer to stick to 'it's work' even if it's
stupid.
Currently, no application can set the frame per second when the device
support it. Why not return a V4L2_STD_WEBCAM, and let applications know how
to use this feature ? because choosing the resolution AND the frame per
second is a standard.

Luc

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