A quick note to remind myself how to get NVME recognized on Dell XPS 15 9570 on Gentoo.

Make sure to add the kernel BLK_DEV_NVME options.

NVM Express block device (BLK_DEV_NVME)
The NVM Express driver is for solid state drives directly
connected to the PCI or PCI Express bus. If you know you
don't have one of these, it is safe to answer N.
To compile this driver as a module, choose M here: the
module will be called nvme.
Symbol: BLK_DEV_NVME [=m]
Type : tristate
Prompt: NVM Express block device
-> Device Drivers
Defined at drivers/nvme/host/Kconfig:1
Depends on: PCI [=y] && BLOCK [=y]