Thanks to Willy Frissen for the info, and joanbm for the patch, which can be found at https://gist.githubusercontent.com/joanbm/7a034ac4b79396c3841040e410ef7e91/raw/b21e792dc0b6f891a4a83d182e0ba9b24b36bd80/nvidia-fix-linux-5.12.patch

I have applied this to 460.56, with Kernel 5.12-rc1, and it compiles successfully, and appears to work OK.     Unable to do a longer test, as my 5.12-rc1 system still crashes with a USB error, after the KVM switches out..

Robert Gadsdon.   March 2nd 2021.