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SubjectRe: USB mini-summit at LinuxCon Vancouver
On Wed, 10 Aug 2011, Theodore Kilgore wrote:

> > Okay, I didn't realize that the different cameras used different webcam
> > drivers as well as different stillcam drivers.
>
> Oh, yes. They are Proprietary devices. And that means what it says. :-)
> And all different from each other, too.
>
> > As far as I can see, there's nothing to stop anybody from adding the
> > stillcam functionality into the webcam drivers right now. If some
> > common code can be abstracted out into a shared source file, so much
> > the better.
> >
> > That would solve the problem, right?
>
> I think everyone involved believes that it would solve the problem.
>
> The question has been all along whether or not there is any other way
> which would work. Also the question of what, exactly, "belongs" in the
> kernel and what does not. For, if something has been historically
> supported in userspace (stillcam support, in this case) and has worked
> well there, I would think it is kind of too bad to have to move said
> support into the kernel just because the same hardware requires kernel
> support for another functionality and the two sides clash. I mean, the
> kernel is already big enough, no? But the logic that Hans has set forth
> seems rather compelling.

The alternative seems to be to define a device-sharing protocol for USB
drivers. Kernel drivers would implement a new callback (asking them to
give up control of the device), and usbfs would implement new ioctls by
which a program could ask for and relinquish control of a device. The
amount of rewriting needed would be relatively small.

A few loose ends would remain, such as how to handle suspends, resumes,
resets, and disconnects. Assuming usbfs is the only driver that will
want to share a device in this way, we could handle them.

Hans, what do you think?

Alan Stern



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