DELL Optiplex 780 - fan lock on low speed after wake up from S3 state

[kszwaba]

I'm using a DELL Optiplex 780 with a modified A15 BIOS for the XEON X3363 processor from
https://239239.blogspot.com/2019/07/microcode-modified-for-dell-optiplex.html
I've noticed that after waking from S3, the fan runs continuously at 950 RPM, regardless of the processor temperature.
Only after restarting the computer does the automatic fan speed control in the BIOS work again.
Then, the CPU speed stabilizes at 1000 RPM under light load and increases smoothly during load to around 1100 RPM at 60-65 degrees Celsius.
i8kfan works and setting fixed speed at 750/1250/2250 RPM depending of the set variable 0/1/2
$ sudo ./dell-bios-fan-control 1
BIOS CONTROL ENABLED
doesn't help return to BIOS controlled fan mode.
I'm using Linux Mint Mate 21.3, kernel 6.8.0-117-lowlatency #117.1~22.04.1-Ubuntu
The problem occurs with both the dell_smm_hwmon module loaded and excluded for load at boot.
Is the described problem related to a BIOS firmware error?
Is it possible to fix it?

Thanks in advance for your help.

[Wer-Wolf]

You can try to either use a recent kernel or load dell-smm-hwmon with fan_max=3 and check if setting the fan state to 3 switches back to automatic mode.

In the second case you can use my fork to control the switch between manual and automatic fan control.