I have a working 2D KDE desktop under Fedora 22 (clean install) with the
nouveau drivers, but 3D things such as steam do not work.

I uninstalled the nouveau driver and installed the nVidia drivers with

        dnf remove xorg-x11-drv-nouveau
        dnf install xorg-x11-drv-nvidia
        dnf install kmod-nvidia
        dnf upgrade


On rebooting I get a black screen where the login (sddm) should be, and
have to switch to a text mode console on Ctrl-Alt-F2 et. al. to get any
further.


The Xorg log contained the following error messages:


[    13.397] (II) Loading /usr/lib64/nvidia/xorg/libglx.so
[    13.475] (II) Module glx: vendor="NVIDIA Corporation"
[    13.475]    compiled for 4.0.2, module version = 1.0.0
[    13.475]    Module class: X.Org Server Extension
[    13.476] (II) NVIDIA GLX Module  346.72  Tue May  5 17:11:15 PDT 2015
[    13.476] (==) Matched nouveau as autoconfigured driver 0
[    13.476] (==) Matched nv as autoconfigured driver 1
[    13.476] (==) Matched modesetting as autoconfigured driver 2
[    13.476] (==) Matched fbdev as autoconfigured driver 3
[    13.476] (==) Matched vesa as autoconfigured driver 4
[    13.476] (==) Assigned the driver to the xf86ConfigLayout
[    13.476] (II) LoadModule: "nouveau"
[    13.479] (WW) Warning, couldn't open module nouveau
[    13.479] (II) UnloadModule: "nouveau"
[    13.479] (II) Unloading nouveau
[    13.479] (EE) Failed to load module "nouveau" (module does not exist, 0)
[    13.479] (II) LoadModule: "nv"
[    13.479] (WW) Warning, couldn't open module nv
[    13.479] (II) UnloadModule: "nv"
[    13.479] (II) Unloading nv
[    13.479] (EE) Failed to load module "nv" (module does not exist, 0)
[    13.479] (II) LoadModule: "modesetting"
[    13.479] (II) Loading /usr/lib64/xorg/modules/drivers/modesetting_drv.so
[    13.480] (II) Module modesetting: vendor="X.Org Foundation"
[    13.480]    compiled for 1.17.1, module version = 1.17.1
[    13.480]    Module class: X.Org Video Driver
[    13.480]    ABI class: X.Org Video Driver, version 19.0
[    13.480] (II) LoadModule: "fbdev"
[    13.480] (II) Loading /usr/lib64/xorg/modules/drivers/fbdev_drv.so
[    13.481] (II) Module fbdev: vendor="X.Org Foundation"
[    13.481]    compiled for 1.17.1, module version = 0.4.3
[    13.481]    Module class: X.Org Video Driver
[    13.481]    ABI class: X.Org Video Driver, version 19.0
[    13.481] (II) LoadModule: "vesa"
[    13.481] (II) Loading /usr/lib64/xorg/modules/drivers/vesa_drv.so
[    13.481] (II) Module vesa: vendor="X.Org Foundation"
[    13.481]    compiled for 1.17.1, module version = 2.3.2
[    13.481]    Module class: X.Org Video Driver
[    13.481]    ABI class: X.Org Video Driver, version 19.0
[    13.481] (II) modesetting: Driver for Modesetting Kernel Drivers: kms
[    13.481] (II) FBDEV: driver for framebuffer: fbdev
[    13.481] (II) VESA: driver for VESA chipsets: vesa
[    13.485] (EE) open /dev/dri/card0: No such file or directory
[    13.485] (WW) Falling back to old probe method for modesetting
[    13.485] (EE) open /dev/dri/card0: No such file or directory
[    13.485] (II) Loading sub module "fbdevhw"
[    13.485] (II) LoadModule: "fbdevhw"
[    13.485] (II) Loading /usr/lib64/xorg/modules/libfbdevhw.so
[    13.485] (II) Module fbdevhw: vendor="X.Org Foundation"
[    13.485]    compiled for 1.17.1, module version = 0.0.2
[    13.485]    ABI class: X.Org Video Driver, version 19.0
[    13.485] (EE) open /dev/fb0: No such file or directory
[    13.485] (WW) Falling back to old probe method for fbdev
[    13.485] (II) Loading sub module "fbdevhw"
[    13.485] (II) LoadModule: "fbdevhw"
[    13.485] (II) Loading /usr/lib64/xorg/modules/libfbdevhw.so
[    13.485] (II) Module fbdevhw: vendor="X.Org Foundation"





So, why is Xorg still trying to load the nouveau driver? What
configuration step have I missed to tell it otherwise?

Any help would be greatly appreciated.

Many thanks,
Chris R.