On 12/29/2018 03:10 AM, Yi Qingliang wrote: > Hello, I encountered a "can't wake_up" problem when use camera on imx6. > > if delay some time after 'streamon' the /dev/video0, then add fd > through epoll_ctl, then the process can't be waken_up after some time. > > I checked both the epoll / vb2_poll(videobuf2_core.c) code. > > epoll will pass 'poll_table' structure to vb2_poll, but it only > contain valid function pointer when inserting fd. > > in vb2_poll, if found new data in done list, it will not call 'poll_wait'. > after that, every call to vb2_poll will not contain valid poll_table, > which will result in all calling to poll_wait will not work. > > so if app can process frames quickly, and found frame data when > inserting fd (i.e. poll_wait will not be called or not contain valid > function pointer), it will not found valid frame in 'vb2_poll' finally > at some time, then call 'poll_wait' to expect be waken up at following > vb2_buffer_done, but no good luck. > > I also checked the 'videobuf-core.c', there is no this problem. > > of course, both epoll and vb2_poll are right by itself side, but the > result is we can't get new frames. > > I think by epoll's implementation, the user should always call poll_wait. > > and it's better to split the two actions: 'wait' and 'poll' both for > epoll framework and all epoll users, for example, v4l2. > > am I right? > > Yi Qingliang > Can you test this patch? Looking at what other drivers/frameworks do it seems that calling poll_wait() at the start of the poll function is the right approach. Regards, Hans Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx> --- diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c index 70e8c3366f9c..b1809628475d 100644 --- a/drivers/media/common/videobuf2/videobuf2-core.c +++ b/drivers/media/common/videobuf2/videobuf2-core.c @@ -2273,6 +2273,8 @@ __poll_t vb2_core_poll(struct vb2_queue *q, struct file *file, struct vb2_buffer *vb = NULL; unsigned long flags; + poll_wait(file, &q->done_wq, wait); + if (!q->is_output && !(req_events & (EPOLLIN | EPOLLRDNORM))) return 0; if (q->is_output && !(req_events & (EPOLLOUT | EPOLLWRNORM))) @@ -2329,8 +2331,6 @@ __poll_t vb2_core_poll(struct vb2_queue *q, struct file *file, */ if (q->last_buffer_dequeued) return EPOLLIN | EPOLLRDNORM; - - poll_wait(file, &q->done_wq, wait); } /*
