Testing the NVIDIA fix on a real PC

For the PC with an RTX 5080 (or any RTX 20 series or newer card) that shows a corrupted picture when gaming mode (gamescope) starts. Branch feature/nvidia-gaming-fix, not released. Background and open work: TODO-nvidia.md; research with sources: NVIDIA-RESEARCH.md.

What the fix does

With a supported NVIDIA GPU (RTX 20 series or newer, same check as the VRAM booster) and its driver installed it

adds nvidia-drm.modeset=1 nvidia-drm.fbdev=1 to the kernel command line (Limine, systemd-boot or GRUB; the file is backed up as <file>.bak-gamescope-wizard),
loads the NVIDIA modules in the initramfs, but only while every installed kernel has them (a pacman hook, /etc/pacman.d/hooks/85-steamify-nvidia-initramfs.hook, decides again at every kernel change),
rebuilds the initramfs and boot entries and checks that the parameters really are in them. It takes effect after a reboot. Older cards (GTX 10 series and older) are left alone.

Before you start

CachyOS with the NVIDIA driver installed (nvidia-open), a user with sudo, git.
Be at the PC and able to see the screen: the last step needs your eyes.
Know the way back (below) in case the PC doesn't boot to a picture: a TTY (Ctrl+Alt+F3) or the boot menu's other kernel entry.

Steps

Get the code:

git clone -b feature/nvidia-gaming-fix https://github.com/theupriser/steamify-cachyos
cd steamify-cachyos

(An existing checkout: git fetch && git checkout feature/nvidia-gaming-fix && git pull.)

Look first, change nothing:

bash tests/nvidia-hardware-test.sh check

Apply the fix (asks for your sudo password), then reboot:
```
bash tests/nvidia-hardware-test.sh apply
```

After the reboot, check again:

bash tests/nvidia-hardware-test.sh check

Start gaming mode, look at the screen, then (from the desktop or a TTY):
```
bash tests/nvidia-hardware-test.sh visual
```
It asks whether the picture was clean and for one line on what you saw.
Send back ~/steamify-nvidia-report.txt (every run adds to it), or start a new session in the checkout and say "read TODO-nvidia.md and the report".

(./steamify.sh from the same checkout also applies the fix, automatically, as part of the SteamOS conversion: there is no menu option for it yet. The script above shows more.)

Reading `check`

Line	Good result	If not
`PASS a supported NVIDIA GPU ... is detected`	your 5080	`FAIL ... older than RTX 20`: the card is skipped on purpose. `FAIL no NVIDIA GPU with its driver`: driver not installed (nouveau?)
`NVIDIA PCI device id 0x... (not on a legacy list ...)`	RTX 20 or newer	on a legacy list: older card
`no chwd legacy lists found`	(note only)	the check cannot tell old from new cards; every card counts as supported. Tell me, it's open item 4 in `TODO-nvidia.md`
`PASS nvidia-drm.modeset=1 is on the running kernel's command line` (and `fbdev=1`)	after step 3 and the reboot	"in the boot loader's file but not booted yet": reboot, or the boot entry used is another one
`PASS nvidia_drm modeset = Y` (and `fbdev = Y`)	after the reboot	`unreadable`: it needs sudo, enter the password
`... early-load drop-in is used / skipped`	note only: skipped means a kernel without the NVIDIA modules is installed	nothing to do

Reading the result

Parameters on, modeset = Y, fbdev = Y, picture clean: the fix works.
Parameters on and Y, picture still corrupted: not this fix. The report has the gamescope and NVIDIA log lines and the versions of nvidia-open, nvidia-utils, gamescope and gamescope-session-cachyos: the cause is probably the gamescope/driver combination for Blackwell (see NVIDIA-RESEARCH.md).
No picture at all after the reboot: undo it (next section) from a TTY or the other kernel entry, and send the report.

Undo

Turning the SteamOS conversion off in the wizard removes the fix too. On its own, from the checkout:

SCRIPT_DIR=$PWD bash -c 'source lib/common.sh; source lib/hdmi-refresh.sh; source lib/vram-booster.sh; source lib/nvidia.sh; nvidia_disable'

It removes the parameters, the early-load file, the pacman hook and its script, and rebuilds the boot entries (reboot after). By hand: delete nvidia-drm.modeset=1 nvidia-drm.fbdev=1 from /etc/default/limine (KERNEL_CMDLINE[default]), /etc/sdboot-manage.conf (LINUX_OPTIONS) or /etc/default/grub (GRUB_CMDLINE_LINUX_DEFAULT), or restore the .bak-gamescope-wizard copy next to it; remove /etc/mkinitcpio.conf.d/90-steamify-nvidia.conf, /etc/pacman.d/hooks/85-steamify-nvidia-initramfs.hook and /usr/local/libexec/steamify-nvidia-initramfs; then sudo limine-mkinitcpio (Limine) or sudo mkinitcpio -P and sudo sdboot-manage gen / sudo grub-mkconfig -o /boot/grub/grub.cfg.

What is and isn't proven

Proven in VMs (QEMU/KVM, CachyOS ISO 260809): the parameters land and survive a reboot on Limine, systemd-boot and GRUB; disabling restores the original; on Limine the pacman hook keeps the early-load file right across kernel reinstalls (with fake NVIDIA modules). Not proven: that the fix cures the 5080's picture, the real NVIDIA modules in the initramfs, DKMS hook order, systemd-boot/GRUB with a pacman transaction, and the RTX 20+ check against a real chwd list. Unit test (no hardware): bash tests/nvidia-test.sh.

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