I posted some of this material in the thread "Lubuntu: acerhdf.conf,"
but am starting a new thread that better reflects what I'm trying to
work out.
According to my current understanding, fans may be controlled by:
1) BIOS/UEFI
2) Bus signalling to PWM controllers governing fans [the lm-sensors
package does this]
3) System Management Mode (SMM) [the i8kutils package does this for many
Dell laptops]
4) ACPI
The above is undoubtedly only a rough description that lacks precision,
but AFAIK it describes well enough the avenues to solutions.
BIOS/UEFI - For this purpose I am working with a Lenovo 3000 C200 laptop
flashed to the latest available version. Its BIOS exposes no
power/thermal management settings. I have heard of Windows programs
that allow reading and even editing of BIOS settings, and I thought it
would be useful to at least know what the hidden BIOS thermal management
settings were. Even better if I could edit them via Linux. I found
dmidecode, biosdecode and the smbios-utils suite, but none of them could
report, much less edit, the thermal management settings. The
coreboot.org project is a BIOS-replacement project, but support is
motherboard specific, the list is short, and my model is not on the
list. There are also some vendor-specific Linux BIOS tools, but these
all seem to be just for flashing the BIOS. So unless I have missed
something, it seems like that avenue comes to a dead end.
lm-sensors - It discovers a sensor for the CPU, loads the coretemp
module, and reports that temperature. But pwmconfig reports "There are
no pwm-capable sensor modules installed." And the lm-sensors
documentation notes in a couple places that it won't work on most
laptops because they lack PWM controllers, and "you have to use acpi
instead." So that's also a dead end.
i8kutils - Many or most Dell laptops are reported to lack not only PWM
controllers but also support for ACPI fan control, so i8kutils uses a
different method, SMM, to control the fans. But the package aims to
support only Dell laptops, and seems to rely on knowledge of specific
motherboard architectures. Another dead end for my purposes.
ACPI - https://wiki.ubuntu.com/DebuggingACPI has the following:
------------------------------------------------------------------------
*Fan Issues *****
These usually relate to the fan spinning too often or too fast. Another
indication may be that the temperature remains high even when the fans
are spinning.
1. Determine if the system has ACPI-based fan control
*
if */proc/acpi/fan* is empty and
*/proc/acpi/thermal_zone/*/trip_points* has no active trip
points (those starting with "AC") then there is no ACPI-based
fan control on your system
2. If the system does have an ACPI-based fan control try booting with
kernel parameter options listed above
------------------------------------------------------------------------
On this laptop, neither /proc/acpi/fan nor
/proc/acpi/thermal_zone/*/trip_points even exist.
But /sys/class/thermal/thermal_zone0 has cdev0_trip_point,
cdev1_trip_point, trip_point_0_temp, trip_point_1_temp,
trip_point_0_type, trip_point_1_type all exist.
Dmidecode or biosdecode reported that the laptop supports ACPI, so the
question may be whether it supports ACPI fan control in particular.
I don't my Linux fundamentals regarding the purposes of /proc and /sys,
but have I just confirmed that this laptop has no ACPI fan control
support, or could it be that trip_points are supported from more than
one location?
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