[lm-sensors] Conversion of ACPI fan+thermal to hwmon sysfs
Henrique de Moraes Holschuh
hmh at hmh.eng.br
Thu Mar 8 14:13:23 CET 2007
On Thu, 08 Mar 2007, Zhang Rui wrote:
> First, ACPI thermal zone can be used to set different cooling policies,
> i.e. passive cooling mode and active cooling mode.
> In passive mode, just as Matthew Garrett described, ACPI thermal may
> throttle the CPU if the passive trip point is triggered, i.e. cool a
> thermal zone by decreasing the performance of the devices(always CPU
> now) in the zone.
> The active cooling mode will use one or more active devices(usually fan)
> to decrease the temperature, which consume extra power. And this is
> really like the way that the hwmon is doing.
> So we can only map the active cooling policy to hwmon, right?
Right, which is not to say we can't extend hwmon to also cover passive.
> Second, one ACPI thermal zone may have more than one fan devices, even
> one active trip point may associate with several fan devices. And this
> seems to be different from the sensors, doesn't it?
No, a LM85 does that too. I don't recall if the current interface allows
for that mapping easily, but if it doesn't, it needs to be modified.
> Third, ACPI can not get/set the fan speed. It can only deal with the fan
> D-state. Fan is on in D0 state and off in D3 state.
That is easy to map to hwmon, you just don't implement some of the pwm
> IMO, the hwmon sysfs interface make it very convenient for users to
> define the desired fan speed depending on a temperature measurement.
> And it seems that we can't take use of this if we map ACPI thermal and
> fan to hwmon-like sysfs interface, right?
Well, it is certainly not easy. I am not really sure the answer is "we
cannot", though, but I don't really have the inclination to break out the
paper and pencil and start thinking *hard* on it right now, sorry :(
> Oh, a _read-only_ interface? Then, it will be much easier.
> But what is it used for?
Monitoring. It is actually used more than the read-write interface...
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