[MT7621] / ramips: Regression in 25.12

May 21, 2026admin

Table of Contents

Describe the bug

Since upgrading my ZBT WG1608 (16M) from OpenWrt 24.10 to 25.12.4, my Fibocom L860-GL LTE modem (operating in CDC-NCM mode via USB) is running continuously hot (~55°C, top end of its spec) even when there is no load/traffic on the router.

On OpenWrt 24.10 the modem idled at a much lower temperature (~40-45°C) under the exact same hardware conditions.

While trying to troubleshoot and manually force USB autosuspend, I also noticed that the standard sysfs endpoints for USB power management are missing in 25.12 for this target:

cat /sys/bus/usb/devices/*/power/control returns “No such file or directory”

cat /sys/module/usbcore/parameters/autosuspend returns “No such file or directory”

Because these controls are missing, I cannot test if manually forcing USB suspend resolves the thermal issue.

OpenWrt version

r32933-4ccb782af7

OpenWrt release

25.12.4

OpenWrt target/subtarget

ramips/mt7621

Device

Zbtlink ZBT-WG1608 (16M)

Image kind

Self-built image

Steps to reproduce

Run OpenWrt 25.12 on the device with a Fibocom L860-GL in CDC-NCM mode via the internal USB bus.

Leave the router at idle with no active traffic.

Actual behaviour

Observe the modem temperature (via AT command: “AT+MTSM=1”) sitting at ~55°C.

Expected behaviour

Modem idle temperature should be ~40-45°C as previously on OpenWrt 24.10.

Additional info

L860-GL firmware version: 18600.5001.00.35.01.42_5001.03.001.005

Diffconfig

Terms