Is PCIE x4 bootable for NVMe SSD under Linux

[dukla2000]

2:
will rootwait=20 fix this?

I didn't have time to try this yet: as far as I search seems rootwait doesn't take parameters. It is by default an infinite wait?
My thought was based on checking the log when booting 4.18 off an SDcard with the NVMe in place. The rootfs mounts around 4s, the PCIe initialises around 11s. It seems to me at 4.18 the rootfs is needed to complete the PCIe initialisation!

A random thought I had, and tried with zero success, was to try a dos partition table with a partition. Works fine for 4.4 but not 4.18.