alt Hacker NewsSure, I think the OP knows this, but another (arguably much more common) way to do fan control is to have a secondary control system (be it a separate management processor, fan IC, management core on the same SoC, whatever) know about temperature curves/thresholds and have that IC handle sensor input to set the PWM.
This is the usual way things are done on x86 with ACPI, for example - unless the OS or some userland fan manager elects to take over via the OSPM fan objects, the fans control is delegated to the BIOS/platform firmware. If I boot an OS with no notion of a fan on a common x86 motherboard, it will still cool reasonably well (usually). Same deal for Macs with SMC - unless the OS tells the SMC explicitly to quit handling the fan, the SMC deals with all the thermals with no intervention.
Replies
Most importantly, even if control was delegated to the CPU, it could still take over in the event of temperature exceeding some safety threshold.
Not wanting to tell on them, my intel SBC super lightweight cigarette-box board has non-PWM risers. you can add a fan, it's always-on. The BIOS doesn't do anything smart it just volts the fan.
I think it's not that unusual for people to delete things they hoped they didn't need, the device targets passive cooling deployments: Turns out a lot of us run them in hot locations.