There is one subtle fact that kernel contributors (as well as members of other "serious" free software project) have to make a point to avoid knowing the intern

There is one subtle fact that kernel contributors (as well as members of other "serious" free software project) have to make a point to avoid knowing the internals of proprietary software, in order to avoid any suspicion of copying the code, design, or willful patent infringement. As such, submitting a patch that relies on such internals in third-party proprietary code and thus imparts a certain amount of knowledge about those internals to the reader might make the work life of the reviewers more difficult. So it is considered distinctly impolite. I'm not 100% sure about the exact legal reasons/mechanisms involved, but this has come up previously during the review of Microsoft's DX12 patches for WSL.