Re: Improving kernel -> userspace (usbfs) usb device hand off

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On Fri, 10 Jun 2011, Alan Stern wrote:

> On Fri, 10 Jun 2011, Felipe Balbi wrote:
> 
> > I don't see any problems in this situation. If, for that particular
> > product, webcam and still image functionality are mutually exclusive,
> > then that's how the product (and their drivers) have to work.
> > 
> > If the linux community decided to put webcam functionality in kernel and
> > still image functionality on a completely separate driver, that's
> > entirely our problem.
> 
> And the problem is how to coordinate the two of them.
> 
> > > 2. Until recently in the history of Linux, there was an irreconcilable 
> > > conflict. If a kernel driver for the video streaming mode was present and 
> > > installed, it was not possible to use the camera in stillcam mode at all. 
> > > Thus the only solution to the problem was to blacklist the kernel module 
> > > so that it would not get loaded automatically and only to install said 
> > > module by hand if the camera were to be used in video streaming mode, then 
> > > to rmmod it immediately afterwards. Very cumbersome, obviously. 
> > 
> > true... but why couldn't we combine both in kernel or in userspace
> > altogether ? Why do we have this split ? (words from a newbie in V4L2,
> > go easy :-p)
> 
> I think the problem may be that the PTP protocol used in the still-cam
> mode isn't suitable for a kernel driver.  Or if it is suitable, it
> would have to be something like a shared-filesystem driver -- nothing
> like a video driver.  You certainly wouldn't want to put it in V4L2.
> 
> > Or, to move the libgphoto2 driver to kernel, combine it in the same
> > driver that handles streaming. No ?
> 
> No.  Something else is needed.
> 
> Alan Stern
> 

Agreed. Something else is needed. But what? Also, very good point about 
PTP.

Theodore Kilgore
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