# BIOS Configuration Fix for CPU Frequency Scaling

## Problem Identified

The CPU was stuck at 1.6 GHz and unable to boost to 4.2 GHz despite all software configurations being correct.

## Root Cause

**Intel SpeedStep Technology** was enabled in BIOS with conflicting settings that prevented dynamic frequency scaling from working properly in Linux.

## Solution

### BIOS Settings Changed:

1. **Intel SpeedStep Technology**: `Disabled`
2. **Power Scheme for AC**: Changed from `Balanced` to `Maximum Performance`

### Location in BIOS:
- **Path**: Config → Power → Intel SpeedStep Technology
- **Original Setting**: [Disabled] or with Mode restrictions
- **New Setting**: Disabled (allows Linux kernel to fully control CPU frequencies)

## Results After BIOS Changes

### On AC Power:
- ✅ **Minimum Frequency**: 400 MHz (deep idle)
- ✅ **Maximum Frequency**: 4200 MHz (full turbo boost)
- ✅ **Dynamic Scaling**: Working perfectly
- ✅ **Power Consumption**: 6-8W idle, up to 25W+ under load

### On Battery:
- ✅ **Minimum Frequency**: 800 MHz (power saving idle)
- ✅ **Maximum Frequency**: 2200 MHz (responsive but battery friendly)
- ✅ **Dynamic Scaling**: Working with TLP configuration
- ✅ **Turbo Boost**: Enabled but capped at 2.2 GHz for better battery life

## Why This Works

When Intel SpeedStep Technology is **enabled** in BIOS:
- BIOS firmware tries to manage CPU frequencies
- This conflicts with Linux kernel's P-state driver
- Results in frequency locks and limited boost capability

When Intel SpeedStep Technology is **disabled** in BIOS:
- Linux kernel has full control via intel_pstate driver
- Dynamic frequency scaling works as intended
- All boost frequencies are accessible
- TLP can properly manage power states

## Current TLP Configuration

### AC Mode (Plugged In):
```bash
CPU_SCALING_MIN_FREQ_ON_AC=800000      # 800 MHz
CPU_SCALING_MAX_FREQ_ON_AC=4200000     # 4.2 GHz (full boost)
CPU_HWP_ON_AC=balance_performance      # Responsive performance
CPU_MAX_PERF_ON_AC=100                 # Allow 100% performance
CPU_BOOST_ON_AC=1                      # Turbo boost enabled
PLATFORM_PROFILE_ON_AC=performance     # Maximum performance
```

### Battery Mode (Unplugged):
```bash
CPU_SCALING_MIN_FREQ_ON_BAT=800000     # 800 MHz
CPU_SCALING_MAX_FREQ_ON_BAT=2200000    # 2.2 GHz (limited boost)
CPU_HWP_ON_BAT=balance_power           # Power efficient
CPU_MAX_PERF_ON_BAT=52                 # Limit to ~52% (2.2 GHz)
CPU_BOOST_ON_BAT=1                     # Turbo enabled but limited
PLATFORM_PROFILE_ON_BAT=balanced       # Balanced for battery
```

## Testing Your Configuration

### Check Current Frequency:
```bash
cat /proc/cpuinfo | grep "cpu MHz"
```

### Monitor Frequency Scaling:
```bash
sudo ./scripts/monitor-cpu-freq.sh
```

### Check Current Status:
```bash
./scripts/cpu-power-control.sh status
```

### Create CPU Load to Test Boost:
```bash
# Single-core intensive task
timeout 10s bash -c 'while true; do echo "scale=5000; 4*a(1)" | bc -l > /dev/null; done'

# Multi-core intensive task
yes > /dev/null &
yes > /dev/null &
yes > /dev/null &
yes > /dev/null &
# Kill with: killall yes
```

## Recommended BIOS Settings for Linux

For optimal CPU frequency scaling and power management on Linux:

### Power Management Settings:
- ✅ **Intel SpeedStep Technology**: `Disabled` (let Linux manage it)
- ✅ **Intel Turbo Boost**: `Enabled`
- ✅ **CPU Power Management**: `Enabled`
- ✅ **Power Scheme (AC)**: `Maximum Performance`
- ✅ **Power Scheme (Battery)**: `Battery Optimized` or `Balanced`

### Thermal Settings:
- ✅ **Adaptive Thermal Management**: `Enabled` (prevents overheating)
- ✅ **Fan Control**: `Auto` or `Automatic`

### Sleep/Idle Settings:
- ✅ **C-States**: `Enabled` (allows deep sleep for power saving)
- ✅ **Enhanced C-States**: `Enabled`

## Troubleshooting

### If CPU is still stuck at low frequency:

1. **Verify BIOS settings were saved**:
   - Reboot and re-enter BIOS
   - Check that SpeedStep is still disabled

2. **Check for conflicting power management**:
   ```bash
   systemctl status power-profiles-daemon
   # If running, it may conflict with TLP
   ```

3. **Restart TLP**:
   ```bash
   sudo systemctl restart tlp
   ```

4. **Check platform profile**:
   ```bash
   cat /sys/firmware/acpi/platform_profile
   # Should be "performance" on AC, "balanced" on battery
   ```

5. **Verify turbo is enabled**:
   ```bash
   cat /sys/devices/system/cpu/intel_pstate/no_turbo
   # Should be 0 (turbo enabled)
   ```

## References

- TLP Documentation: https://linrunner.de/tlp/
- Intel P-state Driver: https://www.kernel.org/doc/html/latest/admin-guide/pm/intel_pstate.html
- ThinkPad BIOS Settings: https://support.lenovo.com/

## Summary

✅ **Problem Solved**: Disabling Intel SpeedStep in BIOS allows Linux full control
✅ **AC Mode**: Full dynamic range 400 MHz - 4.2 GHz
✅ **Battery Mode**: Battery-friendly 800 MHz - 2.2 GHz with turbo boost
✅ **Power Management**: TLP now working as intended