Public bug reported:
Video capture devices made by Epiphan Systems (vendor id 0x2b77) work
once, but as soon as the video device is closed (or even if it is kept
open but the application issues a VIDIOC_STREAMOFF ioctl) it won't work
again - subsequent calls to VIDOC_DQBUF simply hang - until the device
is unbound from and rebound to the uvcvideo module. (modprobe -r
uvcvideo; modprobe uvcvideo also works).
For example:
ffplay /dev/video0 -- works fine and shows the captured stream.
ffplay /dev/video0 -- when run a second time: hangs and does not
capture anything
modprobe -r uvcvideo ; modprobe uvcvideo; ffplay /dev/video -- works
fine again.
Experimenting with the device and the uvcvideo module source code
reveals that problem is the device is expecting SET_INTERFACE(0) to be
sent to return it to a state where it can accept control requests and
start streaming again.
The code in uvc_video.c has several comments stating that some bulk-
transfer devices require a SET_INTERFACE(0) call to be made before any
control commands, even though 0 is already the default and only valid
interface value. And, the function uvc_video_init makes such a call
(which is why the device starts working again after rebinding to the
uvcvideo module). But no such call is made when streaming is stopped
then restarted.
Furthermore, SET_INTERFACE(0) is the mechanism by which isochronous
devices are told to stop streaming, and the comments in
uvc_video_stop_streaming state that the UVC specification is unclear on
how a bulk-based device should be told to stop streaming, so it is
reasonable to expect this particular bulk-based device might be
expecting the same SET_INTERFACE(0) call that an isochronous device
would get as means of being told to stop streaming.
The attached patch fixes the problem for these Epiphan devices by adding
a SET_INTERFACE(0) call in two places. Either one by itself is
sufficient to resolve the symptoms but I think it is probably safest to
include both.
The first hunk adds a SET_INTERFACE(0) call in
uvc_video_start_streaming, but only in the bulk-based case where 0 is
the only possible interface value (it won't mess with an isochronous
device that might be set to a different interface).
The second hunk modifies the behaviour of uvc_video_stop_streaming to
call SET_INTERFACE(0) unconditionally instead of only calling it for
isochronous devices. Since interface 0 should already be set on non-
isochronous devices, it should be safe to set it again, and this way
devices that are expecting it as a signal to stop streaming will get it.
The patch is against 5.4.137 in the vanilla kernel.org source tree, but
also applies cleanly to the 5.8.63 kernel in Ubuntu 20.4 LTS and to the
5.14-rc3 release candidate kernel.
Since this is clearly an upstream issue unrelated to any vendor
modifications, should I also submit an upstream bug report directly to
bugzilla.kernel.org?
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Patch added: "uvc_video.patch"
https://bugs.launchpad.net/bugs/1938669/+attachment/5515189/+files/uvc_video.patch
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https://bugs.launchpad.net/bugs/1938669
Title:
Epiphan framegrabbers stream only once then need unbinding/rebinding
to uvcvideo to work again
Status in linux package in Ubuntu:
New
Bug description:
Video capture devices made by Epiphan Systems (vendor id 0x2b77) work
once, but as soon as the video device is closed (or even if it is kept
open but the application issues a VIDIOC_STREAMOFF ioctl) it won't
work again - subsequent calls to VIDOC_DQBUF simply hang - until the
device is unbound from and rebound to the uvcvideo module. (modprobe
-r uvcvideo; modprobe uvcvideo also works).
For example:
ffplay /dev/video0 -- works fine and shows the captured stream.
ffplay /dev/video0 -- when run a second time: hangs and does not
capture anything
modprobe -r uvcvideo ; modprobe uvcvideo; ffplay /dev/video --
works fine again.
Experimenting with the device and the uvcvideo module source code
reveals that problem is the device is expecting SET_INTERFACE(0) to be
sent to return it to a state where it can accept control requests and
start streaming again.
The code in uvc_video.c has several comments stating that some bulk-
transfer devices require a SET_INTERFACE(0) call to be made before any
control commands, even though 0 is already the default and only valid
interface value. And, the function uvc_video_init makes such a call
(which is why the device starts working again after rebinding to the
uvcvideo module). But no such call is made when streaming is stopped
then restarted.
Furthermore, SET_INTERFACE(0) is the mechanism by which isochronous
devices are told to stop streaming, and the comments in
uvc_video_stop_streaming state that the UVC specification is unclear
on how a bulk-based device should be told to stop streaming, so it is
reasonable to expect this particular bulk-based device might be
expecting the same SET_INTERFACE(0) call that an isochronous device
would get as means of being told to stop streaming.
The attached patch fixes the problem for these Epiphan devices by
adding a SET_INTERFACE(0) call in two places. Either one by itself is
sufficient to resolve the symptoms but I think it is probably safest
to include both.
The first hunk adds a SET_INTERFACE(0) call in
uvc_video_start_streaming, but only in the bulk-based case where 0 is
the only possible interface value (it won't mess with an isochronous
device that might be set to a different interface).
The second hunk modifies the behaviour of uvc_video_stop_streaming to
call SET_INTERFACE(0) unconditionally instead of only calling it for
isochronous devices. Since interface 0 should already be set on non-
isochronous devices, it should be safe to set it again, and this way
devices that are expecting it as a signal to stop streaming will get
it.
The patch is against 5.4.137 in the vanilla kernel.org source tree,
but also applies cleanly to the 5.8.63 kernel in Ubuntu 20.4 LTS and
to the 5.14-rc3 release candidate kernel.
Since this is clearly an upstream issue unrelated to any vendor
modifications, should I also submit an upstream bug report directly to
bugzilla.kernel.org?
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1938669/+subscriptions
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