"Drivers tend to be a world unto themselves, with bugs only
affecting a subset--often a tiny subset--of kernel users. Until a
driver gets merged into the kernel though, anyone wishing to test
it, or help clean it up, has to jump through some hoops. To try and
help reduce those barriers, Linus Torvalds and others have been
advocating early merging of drivers; getting them into the kernel
and incrementally improving them from there.
"This policy of early merging of drivers is not universally
embraced, with a recent remote DMA (RDMA) ethernet driver, which
lives in the infiniband tree, getting singled out..."