thibm: I've tried adding the following to build the kernel with the module:

```nix
  # Enable the `btqca` module in the linux kernel.
  boot.kernelPatches = [
    {
      name = "enable-qca6390-bluetooth";
      patch = null;
      extraConfig = ''
        BT_QCA=y
      '';
    }
  ];

  # Enable the bluetooth driver for the QCA6390.
  boot.kernelModules = [ "btqca" ];
```

However the build process mentioned `BT_QCA=y` to be invalid, so I tried changing it to `BT_QCA y` and the build appears to get much further, however I get `error: unused option: BT_QCA` and the build process fails. Any ideas on what I might be doing wrong here?