The maintainer of the DMA subsystem, Christoph Hellwig seems to vehemently oppose having an mixed-language codebase, and is using the confusion whether he as a maintainer has a say against the consumers of his APIs, to further his cause.

There was indeed some confusion about this, because the normal rule of kernel development is that if you change an API, you also fix the downstream users. (A standard-ish monorepo rule.)

However, because R4L is an experiment, the rule seems to be different: it's up to the R4L team to fix the Rust side if things break, so the upstream C devs don't need to care about Rust if they don't want to. (And conversely, they can't then weaponize their reluctance against Rust. That blade cuts both ways!)

However, apparently there wasn't sufficient clarity about this rule. Well, now there is.