Another problem I had with the irdma driver build mentioned in the previous post is that it would not build with the default kernel in my Ubuntu 20.04 install (5.11.0). However, I knew it would build using 5.4.0 which was present but not automatically selected. The trick is to get grub to default to the desired version. To do this, first list /boot/grub/grub.cfg and find the appropriate string for the desired version. In my case, this was:
Ubuntu, with Linux 5.4.0-42-generic
Then, edit /etc/default/grub and change the GRUB_DEFAULT line to this:
GRUB_DEFAULT="Advanced options for Ubuntu>Ubuntu, with Linux 5.4.0-42-generic"
to activate the new default option and then reboot.