docs: add gunter monitor boot issue investigation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/gunter-monitor-issues.md

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+# Gunter Monitor Boot Issues
+
+## Problem Description
+
+Two of the four monitors on gunter (desktop) intermittently fail to work on startup. The affected monitors are always the two Samsung LS27A600U displays, which are connected via DisplayPort daisy-chaining (MST - Multi-Stream Transport). Power cycling the monitors typically resolves the issue until the next reboot.
+
+## System Configuration
+
+- **GPU**: NVIDIA GeForce RTX 3080 Ti
+- **Driver**: NVIDIA open driver 590.48.01 (beta)
+- **Kernel**: 6.18.8
+- **Compositor**: Hyprland
+
+### Monitor Setup
+
+| Port  | Monitor                  | Resolution     | Connection    |
+|-------|--------------------------|----------------|---------------|
+| DP-1  | Acer XB271HU (center)    | 2560x1440@120Hz | Direct        |
+| DP-3  | BenQ G2420HDBL (top)     | 1920x1080@60Hz  | Direct        |
+| DP-4  | Samsung LS27A600U (right)| 2560x1440@75Hz  | Daisy-chained |
+| DP-5  | Samsung LS27A600U (left) | 2560x1440@75Hz  | Daisy-chained |
+
+The GPU only has 3 DisplayPort outputs, so one Samsung monitor is connected to the other via DP daisy-chaining (MST).
+
+## Diagnostic Findings
+
+### Kernel Errors
+
+The following errors appear in the kernel log during boot (17-27 seconds after boot start):
+
+```
+[drm:nv_drm_dev_load [nvidia_drm]] *ERROR* [nvidia-drm] [GPU ID 0x00000100] Failed to add connector for NvKmsKapiDisplay 0x00000800
+[drm:nv_drm_dev_load [nvidia_drm]] *ERROR* [nvidia-drm] [GPU ID 0x00000100] Failed to get dynamic displays
+```
+
+"Dynamic displays" in NVIDIA terminology refers to MST-connected monitors. These errors indicate the driver is failing to enumerate the daisy-chained displays during initialization.
+
+### Root Cause Analysis
+
+1. **MST timing issues** - The downstream Samsung monitor isn't ready when the driver tries to enumerate the daisy chain during boot
+2. **NVIDIA open driver MST bugs** - The open-source driver (`hardware.nvidia.open = true`) has historically had more MST issues than the proprietary one
+3. **Power sequencing** - The monitors may need more time to negotiate the MST link during cold boot
+
+## Potential Solutions
+
+1. **Switch to proprietary driver** - Change `hardware.nvidia.open = false` in `hosts/gunter/configuration.nix`
+
+2. **Add boot delay for nvidia-drm** - Add kernel parameter `nvidia-drm.load_on_init=0` to defer initialization
+
+3. **Try different nvidia module options** - Add to `boot.extraModprobeConfig`:
+   ```nix
+   options nvidia-drm modeset=1 fbdev=1
+   options nvidia NVreg_PreserveVideoMemoryAllocations=1
+   ```
+
+4. **Check monitor firmware** - Samsung LS27A600U monitors have had MST firmware updates
+
+5. **Reduce link rate during boot** - Lower refresh rate to 60Hz initially to reduce bandwidth requirements
+
+## Useful Diagnostic Commands
+
+### Kernel logs for display/nvidia issues
+```bash
+journalctl -k --no-pager | grep -iE '(nvidia|drm|display|edid|dp|hdmi|monitor)'
+```
+
+### Kernel errors and warnings
+```bash
+journalctl -k --no-pager | grep -iE '(error|fail|warn)'
+```
+
+### Current monitor state (Hyprland)
+```bash
+hyprctl monitors all
+```
+
+### DRM connector status
+```bash
+cat /sys/class/drm/*/status
+ls -la /sys/class/drm/
+```
+
+### GPU and driver info
+```bash
+nvidia-smi --query-gpu=name,driver_version --format=csv,noheader
+```
+
+### Check EDID data for each connector
+```bash
+for f in /sys/class/drm/card1-DP-*/; do
+  echo "=== $(basename $f) ===";
+  cat "$f/enabled" 2>/dev/null;
+  cat "$f/edid" 2>/dev/null | xxd | head -5;
+done
+```
+
+## Related Configuration Files
+
+- `hosts/gunter/configuration.nix` - NVIDIA driver settings
+- `home/hosts/gunter/default.nix` - Hyprland monitor configuration
+
+## Date Investigated
+
+2025-02-06