Pro Max 16 MC16250, fan noise regression, 60% fan floor on AC power (Linux)

System Configuration:

• Model: Dell Pro Max 16 MC16250

• BIOS Version: 1.9.0 and 1.7.0

• OS: Ubuntu 24.04 / 25.04 (OEM Kernel 6.14.0)

• Power Source: Original 130W USB-C and 65W USB-C (Behavior is identical on both)

The Issue: The Embedded Controller (EC) triggers a mandatory "Hard Floor" fan speed of approximately 60% the moment any AC power is detected. This happens even when the system is under zero load and temperatures are well within "Silent" range.

Observed Behavior:

1. On Battery: The system is perfectly silent. CPU temperatures hover at 40°C, and fans stay at 0 RPM.

2. On AC Power: Within seconds of plugging in (130W or 65W), the fans ramp up to 60% and stay there indefinitely, even if the CPU remains at 40°C.

3. Hysteresis: Unplugging the AC power results in the fans stopping almost immediately, proving the trigger is the Power State, not the Thermal State.

Steps Taken to Resolve (All Failed):

• BIOS Settings: Thermal Management set to "Quiet." Intel SpeedStep/SpeedShift toggled Off. Battery Charge Cfg set to "Custom" (stopped at 80%) to reduce charging heat.

• Dell Command | Configure (cctk): Successfully set --ThermalManagement=Quiet and --PrimaryBattChargeCfg=Custom. However, cctk --search and other low-level queries return Segmentation Faults, indicating SMM write-protection is blocking OS-level thermal control.

• Ubuntu Power Management: Set to "Power Saver" mode. CPU frequency successfully capped at 800MHz. Energy Performance Preference (EPP) set to power. Fan speed remained at 60%.

• Kernel Parameters: Tested acpi_enforce_resources=lax and dell_smm_hwmon.force=1. No PWM control files were exposed in /sys/class/hwmon/, confirming the EC is operating in fully autonomous mode and ignoring the OS thermal requests.

• Thermal Zones: All thermal_zone readings (0–9) show temperatures between 20°C and 47°C. There is no "hotspot" justifying 60% fan speed.

Conclusion/Request: The current EC firmware for the MC16250 is too aggressive. It appears to be using a "failsafe" cooling profile for AC power that ignores the actual component temperatures.

Request to Engineering: Please release a BIOS update that allows the "Quiet" thermal profile to maintain 0 RPM fans on AC power when CPU/GPU temperatures are below 50°C.