Looks like mainline then.

You'll need to update to 6.11, which has PCIe merged.

$ lsmod | grep pci
xhci_pci              102400  0
xhci_pci_renesas       65536  1 xhci_pci
pcie_starfive          49152  0
phy_jh7110_pcie        32768  2

$ lsmod | grep nvme

$ ls /sys/class/pci_bus/
0000:00  0000:01  0001:00  0001:01

In reply to @alex:tunstall.xyz
On my system (vendor kernel, not 6.11), it shows up under 0001:00.

What branch of the vendor kernel are you using? I'm building the kernel right now and I have this:

  boot.kernelPackages = let
    starfive_pkg = { lib, fetchurl, buildLinux, ... }@args:
      buildLinux (args // rec {
        version = "6.10.0";
        modDirVersion = version;

        src = fetchurl {
          url = "https://github.com/starfive-tech/linux/archive/37087c6cd7f818990c3c37d2e3cb01b05fc8bb69.tar.gz";
          hash = "sha256-n3By/goN6+SEjd7a8zirhqTZyb6qvqZPDb9TYd4riQI=";
        };

        kernelPatches = [];

        structuredExtraConfig = with lib.kernel; {
          PINCTRL_STARFIVE_JH7110_SYS = yes;
          SERIAL_8250_DW = yes;
        };

        extraMeta.branch = "esmil_starlight";
      } // (args.argsOverride or {}));
  in pkgs.recurseIntoAttrs (pkgs.linuxPackagesFor (pkgs.callPackage starfive_pkg {}));

I went based on activity on GitHub.