For hardware your company owns and intends to ship for years, default to putting the driver in mainline and carrying only the part you have not landed yet. Keep it out of tree when the hardware is not public, the programming interface is still moving, or the code cannot be licensed GPL-compatibl...
Source: [Dev.to](https://dev.to/raghu_bharadwaj_404e60eb0c/in-tree-vs-out-of-tree-driver-where-your-code-should-live-4920)