Changing temperature threshold

[Nate Lawson]

Alexandre "Sunny" Kovalenko wrote:
> On Thu, 2005-06-23 at 14:25 -0700, Nate Lawson wrote:
> 
>>Alexandre "Sunny" Kovalenko wrote:
>>
>>>>When I try to raise hw.acpi.thermal.tz0._CRT to 85C (which is the 
>>>>threshold in the BIOS setup) it doesn't work:
>>>>
>>>>bell# sysctl hw.acpi.thermal.tz0._CRT=3580  # 3580 tenths of Kelvin=85C
>>>>sysctl: oid 'hw.acpi.thermal.tz0._CRT' is read only
>>>>
>>>>Now, my question is: how do I change this value? I've read several
>>>>manpages (acpi(4), acpi_thermal(4), acpiconf(8), loader(8), and many
>>>>others) and checked the handbook, to no avail. Can anyone point me
>>>>to the right direction?
>>>
>>>One of the ways to deal with that would be to dump your ASL (see
>>>Handbook for guidance), find lines which look like:
>>>                        Method (_CRT, 0, NotSerialized)
>>>                        {
>>>                            Return (KELV (0x5d))
>>>                        }
>>>modify them to your liking, compile ASL and override it during boot
>>>(instructions on how to compile and override are in Handbook as well).
>>>Please, note that actual value returned is in the 1/10th of the degree
>>>of Kelvin. Function KELV above has following ASL code associated with
>>>it:
>>>                        Method (KELV, 1, NotSerialized)
>>>                        {
>>>                            Store (Arg0, Local1)
>>>                            Multiply (0x0A, Local1, Local1)
>>>                            Add (Local1, 0x0AAC, Local1)
>>>                            Return (Local1)
>>>                        }
>>>Thermal management chapter of the ACPI specification should provide you
>>>with ample explanation of what this is all about.
>>
>>This explanation is correct.  The reason why the sysctl is read-only is 
>>because the values are supplied by the BIOS and are what the OEM thinks 
>>are critical temperatures.  However, we need a way to allow override in 
>>the case of obviously wrong values like this.  I'll probably change it 
>>to allow overriding from the loader but be read-only in sysctl to avoid 
>>accidental changes from users experimenting.
>>
> 
> Would you consider making ACx levels writeable while you are at that? It
> will make it much easier to implement thermal hysteresis from userland. 

That's pretty scary too.  While not as important as _CRT, if a user 
changes a threshold to a high value, it's possible to damage the system. 
  I'll consider implementing that with some reasonable cap on values.

-- 
Nate