Yocto has supported a PREEMPT_RT kernel as long as I can remember. There are recipes for linux-yocto-rt for the kernel itself, and a core-image-rt image recipe right in poky. It's also pretty straight

Try this one: http://cdn.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patches-5.4.74-rt42.tar.gz Sent with ProtonMail Secure Email.

I see. If you're going to provide the license with the recipe or code, then it needs to be in a subdirectory under the recipe file. So the only one in your tree that matters for this is .../recipes-ic

Bitbake is unable to find the license file because it's looking in the wrong place. If you look at the contents of /media/ice/slow_ext4/yocto_poky/build/tmp/work/armv7vet2hf-neon-poky-linux-gnueabi/ic

I think what you need to do is add the environment variable to BB_ENV_WHITELIST or BB_ENV_EXTRAWHITE: https://www.yoctoproject.org/docs/1.6/bitbake-user-manual/bitbake-user-manual.html#var-BB_ENV_WHIT