Commit 1e07d63749 ("drm/nouveau: add kconfig option to turn off nouveau legacy contexts. (v3)") has caused a build failure for me when I actually tried that option (CONFIG_NOUVEAU_LEGACY_CTX_SUPPORT=n):
,---- | Kernel: arch/x86/boot/bzImage is ready (#1) | Building modules, stage 2. | MODPOST 290 modules | ERROR: "drm_legacy_mmap" [drivers/gpu/drm/nouveau/nouveau.ko] undefined! | scripts/Makefile.modpost:91: recipe for target '__modpost' failed `----
Upstream does not have that problem, as commit bed2dd8421 ("drm/ttm: Quick-test mmap offset in ttm_bo_mmap()") has removed the use of drm_legacy_mmap from nouveau_ttm.c. Unfortunately that commit does not apply in 5.1.9.
Most likely 4.19.50 and 4.14.125 are also affected, I haven't tested them yet.
Cheers, Sven