On Fri, 6 Jul 2012, Laurent Pinchart wrote: > Hi Alan, > > On Friday 06 July 2012 09:50:30 Alan Stern wrote: > > On Fri, 6 Jul 2012, Alan Cox wrote: > > > From: Eric Ding <ericding@xxxxxxxxxxxx> > > > > > > working if I turn it on (e.g., guvcview), then shut it off, wait a few > > > seconds, and then turn it on again. From the second time onward, all I > > > get is screen noise rather than the expected video images. > > > > > > I did a kernel bisection, which revealed the commit that caused the > > > regression: > > > > > > commit e1620d591a75a10b15cf61dbf8243a0b7e6731a2 > > > Author: Rafael J. Wysocki <rjw@xxxxxxx> > > > Date: Fri Mar 18 19:55:36 2011 +0100 > > > > > > USB: Move runtime PM callbacks to usb_device_pm_ops > > > > Can you figure out exactly how that commit caused the problem? As far > > as I can tell, it should not have made any difference to anything. > > That patch has already been pointed out as problematic: > > http://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg48624.html > > (CC'ing the relevant people) Yes, but we still need to know the reason why. Neither Rafael nor I has been able to figure out why that commit messed things up. > > Instead of having all these quirk entries, would it perhaps be better > > to change the uvcvideo driver? It could set the quirk flag every time > > it encounters a Logitech camera. > > Sure, if you think that's a good idea, I can do that. I'm not sure whether all > Logitech webcams require the quirk though. I think it's worth trying. So many of the Logitech webcams do require the quirk, and future ones are likely to require it also. And it's not likely to hurt anything, since (as far as I know) uvcvideo doesn't rely on webcams to retain any state while they aren't in use. > > The main disadvantage would be that the quirk wouldn't get set > > immediately. A camera might be autosuspended before the driver could > > bind to it, and then it might crash when resumed later. Still, I think > > this could be handled. That's the most likely failure mode for the proposed change. To handle it, uvcvideo may need to do a USB device reset in its probe routine. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
