05-03-2015 09:34 PM
My Z40-75 AMD CPU is always stuck at its lowest frequency (1.06Ghz) when returning from sleep. It also happened sometimes when I plugged/unplugged the charger.
I had observed this issue happened both in Windows 8.1 and LInux OS. The current workarounds are rebooting the system or add kernel boot parameter with processor.ignore_ppc=1 (LInux only). Based on the current Linux kernel implementation and previous bug stated here (https://bugzilla.kernel.org/show_bug.cgi?id=23412), cause of this issue is BIOS bug which set cpu_freq bios limit incorrectly on several occassions (e.g sleep, charger plug). Kernel param processor.ignore_ppc=1 is set to ignore this bios limit which is not recommended either because it also bypass the hardware BIOS management.
This bug is quite annoying because when I worked in Windows, I cannot set system to sleep or I must reboot the system.
I have also updated the BIOS with the current version (33) but bug still exists. Lenovo, please fix this!