VIDIOC_QUERYCAP on v4l subdevice - v4l-subdev*

claus.stovgaard at claus.stovgaard at
Tue Nov 1 14:02:16 UTC 2022

Hi folks.

I have also posted on the linux-media mailing list.

In short, I am working on a system based around the Intel Apollo Lake
with an IPU4. The system is having a configuration with a number of
subdevices. Going from v4l-subdev0 to v4-subdev10.

Running gst-device-monitor-1.0 results in a number of errors like.

GStreamer-CRITICAL **: 13:27:36.763:
gst_element_message_full_with_details: assertion 'GST_IS_ELEMENT
(element)' failed        

The reason is because a VIDIOC_QUERYCAP on the subdevice fails.

Looking at the documentation

it states that "All V4L2 devices support the VIDIOC_QUERYCAP ioctl"

On the other hand VIDIOC_QUERYCAP is not part of the subset mentioned
in documentation for V4L2 sub-device.

So is I correct that gstreamer has a bug in gst-device-monitor-1.0, and
it should not try to use the VIDIOC_QUERYCAP ioctl for a sub-device?

It could be that gstreamer should just skip the sub-device.

Notice - gstreamer is 1.20.1 from yocto kirkstone.


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