Re: [PATCH] zr36067: Debugging cleanups (updated again)

Hi Trent, Ronald,

On Fri, 25 May 2007 09:39:34 -0700 (PDT), Trent Piepho wrote:
> I've made a mutli-threaded test application, and the way poll works isn't
> right.  Keep in mind I'm talking about a single process with multiple
> threads sharing the same file descriptor.
> 
> My test will call select() on the zoran capture fd in one thread.  Then,
> while that thread is blocked inside select(), another thread will call
> REQBUFS/QBUF/STREAMON.
> 
> If you don't call poll_wait() to add the v4l capture queue, it doesn't
> work.  select() blocks (poll returning POLLNVAL doesn't cause select to
> return an error) and never returns.  The other thread queues and captures a
> frame, but since the capq wasn't added select never wakes up and sees that
> a frame is ready.
> 
> This is what the log looks like:
> [these syscalls by thread 1]
> DC10plus[0]: VIDIOC_S_FMT - type=1, size=192x128, fmt=0x56595559 (YUYV)
> DC10plus[0]: zoran_poll() - active=F, sync_tail=0/U, pend_tail=0, pend_head=0
> DC10plus[0]: zoran_poll() - no buffers queued
> [thread 1 is now blocked inside select()]
> [following syscalls by thread 2]
> DC10plus[0]: VIDIOC_REQBUFS - type=1
> DC10plus[0]: VIDIOC_QBUF - type=1, index=0
> DC10plus[0]: VIDIOC_QBUF - type=1, index=1
> DC10plus[0]: VIDIOC_STREAMON
> DC10plus[0]: set_vfe() - width = 192, height = 128
> [frame is ready, but select() did not wake, zr->v4l_capq wasn't added]
> [process will just sit here until you interrupt it with a signal]
> 
> After my latest patch, attached, this is what happens:
> 
> [these syscalls by thread 1]
> DC10plus[0]: VIDIOC_S_FMT - type=1, size=192x128, fmt=0x56595559 (YUYV)
> DC10plus[0]: zoran_poll() - active=F, sync_tail=0/U, pend_tail=0, pend_head=0
> [thread 1 is now blocked inside select()]
> [following syscalls by thread 2]
> DC10plus[0]: VIDIOC_REQBUFS - type=1
> DC10plus[0]: VIDIOC_QBUF - type=1, index=0
> DC10plus[0]: VIDIOC_QBUF - type=1, index=1
> DC10plus[0]: VIDIOC_STREAMON
> DC10plus[0]: set_vfe() - width = 192, height = 128
> [kernel select() checks poll status again, since capture started]
> DC10plus[0]: zoran_poll() - active=L, sync_tail=0/P, pend_tail=0, pend_head=2
> [frame still in PEND state, continue to block on select()]
> [frame captured, select() wakes and checks poll status]
> DC10plus[0]: zoran_poll() - active=L, sync_tail=0/D, pend_tail=1, pend_head=2
> [select returns and thread 1 calls DQBUF]
> DC10plus[0]: VIDIOC_DQBUF - type=1

I'm now using this 3rd version of the poll patch, and it works OK for
me.

Thanks,
-- 
Jean Delvare

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