From the config.txt documentation:
If auto_initramfs is set to 1, look for an initramfs file using the same rules as the kernel selection.
Presumably it's looking for something with either no suffix, 7
, 7l
, or 8
, but what is the base name for that?
update-initramfs
generates files named initrd.img-$(uname -r)
, but it's not that.
Neither initrd.img
nor imitramfs.img
are loaded for kernel.img
.