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RFC: V4L2 MPEG Encoding API: Part 1

On Monday 01 May 2006 22:01, Alan Cox wrote:
> On Mon, May 01, 2006 at 09:40:32PM +0200, Hans Verkuil wrote:
> > Now, one option is to add another ioctl command. But there are
> > already a lot of them in V4L2, and adding one that might be used by
> > only one specific device seems a bad idea to me. It would also mean
> > that while the other settings are done by controls, this particular
> > property is now set using an ioctl. Confusing, I think.
>
> We already have chip specific private ioctl numbers so that part is
> fine if it is unique to the chip. If not as you say then it is not
> ideal.

I don't believe that chip specific private ioctls are used anywhere in 
video4linux (except perhaps for some things internal to v4l). I may be 
wrong here, though. Another advantage of controls is that the 
application can query them, get the name of the control and other type 
information. A private ioctl is an alternative to a chip-specific 
control, though. I'll have to look into that further.

> > If you have better ideas or suggestions, please let me know! That's
> > why it's an RFC after all.
>
> Not my favourite but I think this will get asked on the main kernel
> list so should be looked at, and may indeed be the best - using sysfs?

The intention for 2.6.18 or 2.6.19 is to export all controls to sysfs by 
default. This isn't implemented yet, but the experiences with the 
pvrusb2 driver (currently v4l_experimental) which supports this are 
very positive. So if you define something as a control you should get 
the sysfs interface for free once it is implemented.

Regards,

	Hans

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