Re: [lm-sensors] Fintek f71882fg ACPI conflict

[Michael Zintakis <michael.zintakis@xxxxxxxxxxxxxx>]

> > Could any of the more knowledgeable on here explain why
> > is it such a bad idea please?
> >     
>
> Because there's no handshaking between the firmware and the OS driver, 
> and accesses to hardware sensors are often indexed. Imagine this 
> scenario:
>
> ACPI                             lmsensors
> ----                             ---------
> select temperature register
>                                  select fan speed register
> read value
>                                  read value
>
> ACPi will read the fan speed register instead of the temperature 
> register, and the value may be far too high and cause a critical 
> shutdown of the system.
>
> That's the *good* outcome. The bad outcome involves these register 
> accesses racing in a way that disables fan control or thermal trip 
> points and risks causing hardware damage. It's not safe for two 
> different codepaths to access the same hardware without having any kind 
> of locking, so if your system firmware declares that ACPI is using the 
> temperature device the hardware sensors framework will refuse to.
>   
All noted, thanks for the explanation - pretty hairy stuff! The tragic 
thing is, I have no way of telling ACPI to *not* use or "implement" its 
own fan, voltage, temperature management and let a more capable piece of 
software (the f71882fg driver in this case) do that job!

What is the alternative? There is none that I could see. I tried using 
memmap to force ACPI not to use the memory region claimed by f71882fg 
(0x290 - 8 bytes long according to the driver), but that didn't help 
much. What am I supposed to do - deactivate ACPI completely? That would 
be like going after a fly with a bazooka!
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