FFS_ROOT is gone?

Hello,

my kernel (5.1-REL) can't mount root (mountroot>) on my CF-card although
it's booting fine and I can mount the card on my USB card reader.
I had a look at GENERIC and saw that I didn't miss the option FFS_ROOT but
it doesn't exist any longer.
Any ideas why I can't mount root?
The card is found correctly as ad0

Thanks,

-Harry