Gah, I've found the issue. Based on the investigation in this thread https://www.raspberrypi.org/forums/viewtopic.php?f=98&t=174347&start=25#p1120478 I narrowed it down to dtparam=i2c_arm=on preventing the secondary camera from being detected.
After commenting out dtparam=i2c_arm=on from /boot/firmware/syscfg.txt I now have /dev/video0 and /dev/video1 for each of the supported cameras on CM3+ in Ubuntu 20 [ 14.133985] bcm2835-v4l2: V4L2 device registered as video0 - stills mode > 1280x720 [ 14.139034] bcm2835-v4l2: Broadcom 2835 MMAL video capture ver 0.0.2 loaded. [ 14.151264] bcm2835-v4l2: V4L2 device registered as video1 - stills mode > 1280x720 [ 14.156258] bcm2835-v4l2: Broadcom 2835 MMAL video capture ver 0.0.2 loaded. Is it expected that this, remotely related, setting affects functionality in bcm2835-camera.c? That's pretty brittle. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1904306 Title: bcm2835-v4l2 does not detect/expose the second camera on RPi Compute Module 3+ in Ubuntu Server 20.04.1 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/libv4l/+bug/1904306/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs