Hi everybody, Those two RFC patches convert the uvcvideo driver to videobuf2. The transition was pretty smooth, except for an issue with videobuf2 and hot-pluggable devices. When a hot-pluggable device is disconnected, all pending video buffers must be marked as erroneous and waiters must be woken up. Drivers (and/or videobuf2) must then not allow new buffers to be queued, otherwise applications would wait forever on VIDIOC_DQBUF (side note: maybe it's time for V4L2 to explictly state what should happen in that case, and what error codes must be returned). This isn't a big issue in itself, except that handling the disconnection event in QBUF introduces a race condition. Fixing it can only be done with the help of a spinlock which must be held across the disconnection check and the list_add_tail call in buf_queue. Unfortunately, buf_queue returns void, which prevents checking for the disconnection event there. There are multiple ways to solve this problem. the one I've implemented in this RFC modifies buf_queue to return an error code, and lets drivers implement buffers queue cancellation on disconnect. As this could be a tricky problem, a better solution might be to move disconnection handling inside videobuf2. The downside is that a new spinlock will be needed in videobuf2. Yet another solution would be to let QBUF succeed, but marking the buffer as erroneous and waking up userspace immediately. I don't like this though, as the error flag on buffers is meant to indicate transcient errors, and device disconnection is more on the fatal error side :-) Laurent Pinchart (2): v4l: videobuf2: Handle buf_queue errors uvcvideo: Use videobuf2 drivers/media/video/uvc/Kconfig | 1 + drivers/media/video/uvc/uvc_isight.c | 10 +- drivers/media/video/uvc/uvc_queue.c | 494 ++++++++++------------------------ drivers/media/video/uvc/uvc_v4l2.c | 19 +-- drivers/media/video/uvc/uvc_video.c | 30 +- drivers/media/video/videobuf2-core.c | 32 ++- drivers/usb/gadget/uvc.h | 2 +- include/linux/uvcvideo.h | 37 ++-- include/media/videobuf2-core.h | 2 +- 9 files changed, 203 insertions(+), 424 deletions(-) -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
