# 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