Re: [PATCH v6 0/5] Add ZynqMP VCU/Allegro DVT H.264 encoder driver

[Michael Tretter <m.tretter@pengutronix.de>]

On Wed, 22 May 2019 14:04:23 +0200, Hans Verkuil wrote:
> On 5/13/19 7:21 PM, Michael Tretter wrote:
> > This is v6 of the Allegro DVT H.264 encoder driver found in the EV
> > family of the Xilinx ZynqMP platform.
> > 
> > Only minor changes this time. I dropped the implementation of the
> > selection api, removed all references mentioning the decoder, and fixed
> > a few issues reported by sparse and smatch.
> > 
> > The v4l2-compliance result using the current vicodec branch is
> > 
> > v4l2-compliance SHA: c2ad13e4b7aef9ae160303189c67a91e1775f025, 64 bits
> > 
> > Compliance test for allegro device /dev/video4:
[...]
> > I observed that the "MMAP (select)" test occasionally fails, because the
> > test did not receive an V4L2_EVENT_EOS when dequeuing a buffer with
> > V4L2_BUF_FLAG_LAST being set. The driver always queues the event before
> > returning the last buffer and the "MMAP (epoll)" does not fail. Thus, I
> > decided to send the series anyway.  
> 
> Where exactly does v4l2-compliance fail? This is weird, and I believe
> this warrants a bit more debugging. I recommend adding a debug
> statement in allegro_channel_buf_done() to see when a buffer is marked
> LAST.

v4l2-compliance fails in line 1074

	fail: v4l2-test-buffers.cpp(1074): !got_eos && !got_source_change

The corresponding code in v4l2-compliance is

	if (buf.g_flags() & V4L2_BUF_FLAG_LAST) {
		fail_on_test(buf.dqbuf(node) != EPIPE);
>		fail_on_test(!got_eos && !got_source_change);
		if (!count)
			break;
		fail_on_test(node->streamoff(m2m_q.g_type()));
		m2m_q.munmap_bufs(node);

When the test fails, the select/epoll_wait returns with readable data,
but without readable events on the last buffer. If the test is
successful, data and events are available. This looks like a race
between the event and the LAST buffer and if the LAST buffer comes
first, the test fails.

As said, the driver always queues the EOS event before calling
v4l2_m2m_buf_done() on the LAST buffer. Right now, I don't understand
how this can happen, but I will continue debugging.

> 
> These tests really should not fail, and it is a strong indication of a
> bug somewhere.
> 
> I don't want to merge a driver that has a FAIL in v4l2-compliance without
> at the very least understanding why that happens. Ignoring it defeats the
> purpose of v4l2-compliance.

Totally agreed.

Michael

> 
> Regards,
> 
> 	Hans
>