Is PCIE x4 bootable for NVMe SSD under Linux

[dukla2000]

At 4.4 the pcie & nvme initialisation is ready before the rootfs is mounted (even though I am booting off the SDcard).
At 4.18 the pcie & nvme initialisation only happens way after the rootfs is mounted.

To my best knowledge, it means Kernel -4.4 has pcie & nvme modules built into the Linux image, and Kernel -4.18 has pcie & nvme modules as external loadable modules (drivers).

Because we want rootfs on NVMe which plugged in PCIe slot,  so both pcie & nvme need to be loaded before rootfs is mounted.

If Ayufan can compile Kernel -4.18 as the same way as his compiled Kernel -4.4, (hopefully in the final release version, he will do) then everything should work.

I opened an issue on github - Ayufan says we must use initramfs. (Which makes sense as it is only the RockPro64 that needs these modules.)

So now to work out how to cook an enhanced initramfs. (And it is probably the same issue with eMMC not working at 4.18?)