bcmdhd.ko not loading

Hope someone can help with this - or at least point me in the right direction.
I put together a new BSP with R28.2 for our TX1 board.
I think it should be pretty close to the kernel and rootfs used on the Nvidia TX1 Dev Board.

The issue is that the bcmdhd.ko does not load at boot time so I cannot use WiFi.
With our previous BSP built from R24, this all worked fine.

I get these messages in syslog:

vimo@vimo-r28:~$ sudo grep -i bcmdhd /var/log/syslog 
Jun 27 20:22:34 vimo-r28 systemd-udevd[338]: Error running install command for bcmdhd
Jun 27 20:22:34 vimo-r28 systemd-udevd[329]: Error running install command for bcmdhd
Jun 27 20:32:44 vimo-r28 kernel: [  617.027834] found wifi platform device bcmdhd_wlan
Jun 27 20:32:44 vimo-r28 kernel: [  617.296232] Compiled in drivers/net/wireless/bcmdhd on Jun 26 2018 at 17:20:38
Jun 27 20:32:45 vimo-r28 kernel: [  617.503510] Compiled in drivers/net/wireless/bcmdhd on Jun 26 2018 at 17:20:38

I am not even sure where to look for the install command for bcmdhd.

I can fix this issue after boot by issuing the command:
sudo insmod /lib/modules/4.4.38-vimo2+/kernel/drivers/net/wireless/bcmdhd/bcmdhd.ko

This seems to load it alright - then I can use WiFi.
But I would like to find out why it isn’t loading during boot time. If this is failing, maybe something else is failing. Can someone tell me where to look or what to check.

rob.brownlee,

According to your comment, did you mean you are not using the default rootfs from Jetpack?

Right. Sorry. We are not using the default rootfs.
We used debootstrap to build a generic rootfs from xenial.