docs: NVIDIA-RESEARCH.md and TODO: hook VM results, opt-out toggle plan, older cards

.no-release-yet

@@ -1,4 +1,4 @@
 This branch is not ready to be released: do not merge it into the release branch.
 When the feature is complete and tested, ask the user whether it may be released;
 on a yes, delete this file, then open the pull request into the release branch.
-Open work and how to pick it up: TODO-nvidia.md.
+Open work and how to pick it up: TODO-nvidia.md. Research notes: NVIDIA-RESEARCH.md.

NVIDIA-RESEARCH.md

@@ -0,0 +1,63 @@
+# NVIDIA and gamescope: research notes (branch `feature/nvidia-gaming-fix`)
+
+Written 2026-10-01 for the NVIDIA fix (`lib/nvidia.sh`). Delete with `TODO-nvidia.md` and
+`.no-release-yet` when the feature is released, or move what is still useful to `TECHNICAL.md`.
+"Verified" means seen in this session (a VM run or a fetched page); the rest is from search results or memory.
+
+## The user's PC
+RTX 5080 (Blackwell). Blackwell only works with NVIDIA's open kernel modules (`nvidia-open`), driver 570+.
+The corrupted picture at gaming mode start is not diagnosed yet: the fix adds kernel parameters, the real cause
+may be the gamescope/driver combination. `tests/nvidia-hardware-test.sh` collects the facts.
+
+## What the fix changes and why (reasoning, not proven for gamescope)
+- gamescope runs the display itself through DRM/KMS. With NVIDIA that needs `nvidia-drm.modeset=1`; `nvidia-drm.fbdev=1`
+  gives the console a framebuffer from `nvidia-drm`, so the hand-off from the console to gamescope is clean.
+- Loading the NVIDIA modules in the initramfs (early KMS) only changes how early boot looks (native resolution,
+  splash, passphrase prompt), not speed. It is not needed for gamescope, which starts after login (believed, not proven).
+- No source found that mentions these parameters for gamescope; the fix is a standard NVIDIA/Wayland setup, applied
+  automatically. Whether it cures the 5080's picture is only known after `tests/nvidia-hardware-test.sh`.
+
+## Which cards (the user hopes older than RTX 2000 work)
+- Open kernel modules: Turing (RTX 20, GTX 16) and newer only; they need the GSP processor first built into Turing.
+  Maxwell, Pascal and Volta (GTX 900/10 series, Titan V) only work with the proprietary driver, whose legacy branch
+  is 580. Source: [NVIDIA README, open kernel modules](https://download.nvidia.com/XFree86/Linux-x86_64/560.35.03/README/kernel_open.html),
+  [NVIDIA datacenter driver guide, kernel modules](https://docs.nvidia.com/datacenter/tesla/driver-installation-guide/kernel-modules.html).
+- `nvidia-drm.modeset` and `fbdev` are options of the `nvidia-drm` module in both flavours, so the fix applies to
+  any card whose driver provides `nvidia_drm` (what `nvidia_present` tests: GPU vendor 0x10de + `modinfo nvidia_drm`).
+  Whether gamescope then works on an older card is a different question, and no source says the fix helps there.
+- Not NVIDIA's proprietary driver: nouveau has no `nvidia_drm`, so the fix does nothing. The CachyOS handheld ISO boots
+  GTX 10xx and older with nouveau until the NVIDIA driver is installed
+  ([CachyOS forum](https://discuss.cachyos.org/t/information-experimental-cachyos-handheld-edition/203)).
+
+## Known gamescope problems that are not this fix
+- **GTX 1050 Ti (Pascal), driver 580.119.02, gamescope newer than 3.16.16:** the CachyOS handheld session fails to start when
+  a display is on the GPU's HDMI port (back to the TTY, loop). Workarounds: downgrade `gamescope` and `lib32-gamescope`
+  to 3.16.16, or use the motherboard's video port. Fixed upstream? unknown.
+  [CachyOS forum](https://discuss.cachyos.org/t/no-display-on-cachyos-handheld-edition-on-nvidia-with-gamescope-3-16-16/20935)
+- **VRS on PCs:** CachyOS' gamescope-session enables variable rate shading (`STEAM_USE_DYNAMIC_VRS=1`,
+  `RADV_FORCE_VRS_CONFIG_FILE`, `echo 1x1 > ...` in `/usr/lib/steamos/gamescope-session`). It broke rendering (missing
+  floors/lighting, bad post-processing) on a PC with an AMD RX 6800 XT. RADV is AMD's driver: not the NVIDIA corruption.
+  Workaround: comment those three lines, or per game `env -u RADV_FORCE_VRS_CONFIG_FILE STEAM_USE_DYNAMIC_VRS=0 %command%`.
+  [CachyOS forum](https://discuss.cachyos.org/t/cachyos-gamescope-session-asset-missing-vrs-fix/34971)
+- gamescope's DRM backend needs Vulkan DRM format modifiers; with the open Mesa driver NVK that came in Mesa 24.1
+  ([GamingOnLinux](https://www.gamingonlinux.com/2024/05/nvk-driver-gets-drm-format-modifiers-to-work-with-gamescope-in-mesa-24-1)).
+  The proprietary driver had format-modifier trouble with gamescope too (GitHub issues
+  [ValveSoftware/gamescope#1662](https://github.com/ValveSoftware/gamescope/issues/1662),
+  [#1516](https://github.com/ValveSoftware/gamescope/issues/1516): titles seen only, not read).
+
+## What was verified in VMs (QEMU/KVM, CachyOS ISO 260809)
+- Kernel parameters land and survive a reboot on Limine, systemd-boot and GRUB; disable restores the original.
+- Limine's tool is a compiled program: an appended `KERNEL_CMDLINE[default]+=" ..."` line was pasted into the kernel
+  command line as text; the fix edits the existing `KERNEL_CMDLINE[default]="..."` line.
+- `mkinitcpio` fails on a MODULES entry a kernel lacks; `limine-mkinitcpio` then skips that kernel's initramfs and boot
+  entry (parameters included); systemd-boot/GRUB image: "may not be complete" (not run with failing modules).
+- Real CachyOS/Limine pacman hooks: `10-limine-snapper-lock`, `60-limine-mkinitcpio-remove-pre`, `60-mkinitcpio-remove`,
+  `80-limine-efi-deploy`, `90-limine-mkinitcpio-remove-post`, `90-mkinitcpio-install`; Steamify's hook is `85-`
+  (DKMS's is `71-dkms-install`, not installed in the VM). A mirror older than the ISO "downgrades" kernels on reinstall.
+- The hook keeps the early-load drop-in right across kernel changes (see `TODO-nvidia.md`).
+
+## Still unknown (needs the hardware)
+- Does the fix cure the 5080's corrupted picture? Which gamescope/driver versions does the PC have?
+- Does it help, harm or do nothing on Maxwell/Pascal/Volta cards? No older card available yet.
+- Real NVIDIA modules in the initramfs (VMs only had renamed fake modules); DKMS hook order on a PC with
+  `nvidia-open-dkms`.

TODO-nvidia.md

@@ -1,6 +1,6 @@
 # TODO: NVIDIA fix for gaming mode (branch `feature/nvidia-gaming-fix`)
 
-Delete this file together with `.no-release-yet` when the feature is released.
+Delete this file, `NVIDIA-RESEARCH.md` and `.no-release-yet` when the feature is released.
 Written 2026-10-01 so a new session can pick this up.
 
 ## Problem
@@ -28,12 +28,43 @@ missing, or a gamescope/driver mismatch.
   Limine pasted an appended `+=` line as text into the cmdline; a kernel without the
   NVIDIA modules made limine-mkinitcpio skip its boot entry.
 
-## In progress (2026-10-01)
-- Kernel changes: the early-load drop-in is now kept right by a pacman hook
-  (`patches/steamify-nvidia-initramfs.{sh,hook}`, installed by `nvidia_enable`). Unit-tested
-  (29 checks). **Not yet VM-tested with a real pacman transaction**: hook order (85- after
-  71-dkms-install, before the mkinitcpio/limine hooks: check the real hook names in
-  /usr/share/libalpm/hooks), a kernel reinstall with and without modules.
+## Kernel changes (done, VM-tested 2026-10-01, Limine)
+The early-load drop-in is kept right by a pacman hook (`patches/steamify-nvidia-initramfs.{sh,hook}`,
+installed by `nvidia_enable`, `/etc/pacman.d/hooks/85-steamify-nvidia-initramfs.hook`). Real pacman
+transactions in a Limine VM: the hook runs between "Updating module dependencies" and "Updating
+linux initcpios" (real hook names there: 60-*-remove, 80-limine-efi-deploy, 90-limine-mkinitcpio-remove-post,
+90-mkinitcpio-install; DKMS would be 71-): the drop-in is present while every kernel has the modules, removed
+when the LTS kernel loses them, back when they return; initramfs nvidia files 1 -> 5 -> 1 -> 5 -> 1
+(1 = baseline, 4 modules added); no ERROR/skipping in any rebuild; cmdline kept the parameters after a reboot;
+disable removes hook, script and drop-in. Found on the way: an empty hook/script was installed when
+`patch_file` failed (now an error). Only tested with fake modules (renamed copies of a small module), on
+Limine; systemd-boot and GRUB use the same hook but were not run with pacman transactions.
+
+## Opt-out toggle (new request, 2026-10-01: not built yet)
+When a compatible NVIDIA card is listed there should be a menu option, on by default (opt-out), named
+"NVIDIA compatibility", as a sub-option of the SteamOS conversion, directly under "Boot into" (`boot`).
+Today the fix runs unconditionally inside `gaming_enable`/`gaming_disable`.
+- [ ] New component `nvidia` in `lib/menu.sh`: `COMPONENTS` right after `boot`, `PARENT[nvidia]=gaming`, `LABEL`,
+      `FEATURE_VERSION[nvidia]`, `component_available` -> `nvidia_available` (= `nvidia_present`); not in
+      `NO_PRESELECT` (ticked by default, `feature_new` ticks it for installs that already have the conversion).
+      `nvidia_status` from the system (hook + parameters present), `nvidia_enable`/`nvidia_disable` = the code now
+      called from `gaming_enable`/`gaming_disable` (remove those calls). Check `toggle_component` dependencies,
+      `feature_record_unticked`, the plan texts ("This will: ...").
+- [ ] The app: `ui/qml/Texts.qml` item texts, `AppState.qml`, the screen rows, `lib/backend.sh` if it lists ids;
+      `--defaults [--options <ids>]` (the Steam Machine ISO's installer pages: it names the ids) and `--skip`.
+- [ ] README rows/screenshot rule (a release that adds a menu row retakes `assets/screenshot-menu.png`), TECHNICAL.md,
+      CHANGELOG, `tests/nvidia-test.sh` (status/enable/disable through the component), VM menu test in
+      steamify-cachyos-dev (`share/vmtest/menu`, TESTPLAN.md row).
+- [ ] What "compatible" means: see the research below. The parameters themselves apply to any card whose driver
+      provides `nvidia_drm` (what `nvidia_present` tests); whether gamescope works on a card is a separate question.
+
+## Older cards and other research
+The user hopes the fix also works for GPUs older than RTX 2000. Full notes with sources: **`NVIDIA-RESEARCH.md`**.
+Short version: open kernel modules need Turing+, Maxwell/Pascal/Volta need the proprietary driver (580 legacy branch);
+`nvidia-drm.modeset/fbdev` exist in both, so the fix applies to any card with `nvidia_drm`, but nothing found says gamescope
+works better or worse there (a GTX 1050 Ti has a known gamescope>3.16.16 start problem on HDMI, not ours). Cannot be promised:
+needs a test on a real older card. Design for the toggle: on by default for any card with `nvidia_drm`, the label says
+what it does, `tests/nvidia-hardware-test.sh` reports GPU and driver so results can be compared.
 
 ## Still to do
 1. [ ] **On the NVIDIA PC** (only place the real fix can be judged), from this checkout:
@@ -45,10 +76,11 @@ missing, or a gamescope/driver mismatch.
    gamescope/NVIDIA log lines and the versions (`nvidia-open`, `nvidia-utils`, `gamescope`,
    `gamescope-session-cachyos`); the cause is then probably a gamescope/driver mismatch
    for Blackwell, not this fix.
-3. [ ] Not covered by any test: the early-load drop-in on a machine that has the modules
-   (the VMs have none), and a boot loader other than the three.
+3. [ ] Not covered by any test: the early-load drop-in with the REAL NVIDIA modules (the VMs only have renamed
+   fake ones), and systemd-boot/GRUB with a pacman transaction (only Limine was run).
 4. [ ] Changelog: fill in the commit hashes of this feature's lines (next commit, per AGENTS.md).
-5. [ ] When complete and tested: ask the user whether it may be released. On a yes delete
+5. [ ] Build the opt-out toggle (section above) before release.
+6. [ ] When complete and tested: ask the user whether it may be released. On a yes delete
    `.no-release-yet` and this file, open the PR into `release/2.9.7` (local branch only so
    far, one commit `chore: Version 2.9.7`; push it then) and merge it. The user merges
    `release/2.9.7` into `main`.