Until recently, that “support” had been a barely supported forks of the linux kernel that were barely updated, and was so locked down that custom rom support was a pipedream on snapdragon processors. Which to be fair, is par for the course on most ARM chipsets (It’s the reason you see a lot of custom roms for android have extremely old and outdated kernels)
I’m glad to see more ARM companies moving towards working with upstream projects, and not just making working on their stuff a PITA to protect “Trade Secrets” or some bullshit like that.