How to store files before filesystem is mounted

I've a kernel driver that looks for a number of binaries (to load into a device) before an ext4 file system is mounted. I'm wondering if this is part of initrd, or initramfs that we're talking about, or something else altogether.

I'm using Image Tree Blob (.itb) with kernel, and ramdisk included. Those binaries currently are stored into ramdisk.

One option is to delay starting of the kernel driver. I'm however exploring the option of making those binaries available earlier.

Any idea?