[PATCH v5 00/39] i.MX Media Driver

[Russell King - ARM Linux]

On Sat, Mar 18, 2017 at 12:58:27PM -0700, Steve Longerbeam wrote:
> Right, imx-media-capture.c (the "standard" v4l2 user interface module)
> is not implementing VIDIOC_ENUM_FRAMESIZES. It should, but it can only
> return the single frame size that the pipeline has configured (the mbus
> format of the attached source pad).

I now have a set of patches that enumerate the frame sizes and intervals
from the source pad of the first subdev (since you're setting the formats
etc there from the capture device, it seems sensible to return what it
can support.)  This means my patch set doesn't add to non-CSI subdevs.

> Can you share your gstreamer pipeline? For now, until
> VIDIOC_ENUM_FRAMESIZES is implemented, try a pipeline that
> does not attempt to specify a frame rate. I use the attached
> script for testing, which works for me.

Note that I'm not specifying a frame rate on gstreamer - I'm setting
the pipeline up for 60fps, but gstreamer in its wisdom is unable to
enumerate the frame sizes, and therefore is unable to enumerate the
frame intervals (frame intervals depend on frame sizes), so it
falls back to the "tvnorms" which are basically 25/1 and 30000/1001.

It sees 60fps via G_PARM, and then decides to set 30000/1001 via S_PARM.
So, we end up with most of the pipeline operating at 60fps, with CSI
doing frame skipping to reduce the frame rate to 30fps.

gstreamer doesn't complain, doesn't issue any warnings, the only way
you can spot this is to enable debugging and look through the copious
debug log, or use -v and check the pad capabilities.

Testing using gstreamer, and only using "does it produce video" is a
good simple test, but it's just that - it's a simple test.  It doesn't
tell you that what you're seeing is what you intended to see (such as
video at the frame rate you expected) without more work.

> Thanks, I've fixed most of v4l2-compliance issues, but this is not
> done yet. Is that something you can help with?

What did you do with:

ioctl(3, VIDIOC_REQBUFS, {count=0, type=0 /* V4L2_BUF_TYPE_??? */, memory=0 /* V4L2_MEMORY_??? */}) = -1 EINVAL (Invalid argument)
                test VIDIOC_REQBUFS/CREATE_BUFS/QUERYBUF: OK
ioctl(3, VIDIOC_EXPBUF, 0xbef405bc)     = -1 EINVAL (Invalid argument)
                fail: v4l2-test-buffers.cpp(571): q.has_expbuf(node)
                test VIDIOC_EXPBUF: FAIL

To me, this looks like a bug in v4l2-compliance (I'm using 1.10.0).
I'm not sure what buffer VIDIOC_EXPBUF is expected to export, since
afaics no buffers have been allocated, so of course it's going to fail.
Either that, or the v4l2 core vb2 code is non-compliant with v4l2's
interface requirements.

In any case, it doesn't look like the buffer management is being
tested at all by v4l2-compliance - we know that gstreamer works, so
buffers _can_ be allocated, and I've also used dmabufs with gstreamer,
so I also know that VIDIOC_EXPBUF works there.

-- 
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