cpufreq on 5.4R

[Nate Lawson]

Takashi Inoue wrote:
> Hi Nate,
> 
> Thanks for your post.
> 
>> Only acpi_throttle is supported in the 5.4 version of cpufreq.  I'm 
>> hoping to get an MFC of the -current version in soon although there 
>> are a couple nits I'd like to fix there first.
> 
> I see. I'll try the throttle. I hope your excelent works are MFCed to 5 
> soon.

acpi_throttle is compiled into acpi.ko so if you are using ACPI, you 
already have acpi_throttle available if your system supports it.

>> I'm not sure the port works properly with cpufreq.  A better thing is 
>> to use the est.c from -current.  Or just wait for MFC.
> 
> I see. I'll also try cvsup current cpufreq when I have time.
> By the way,  I cannot see the difference between est and ichss.
> Should I use est insted of ichss? ThinkPad X40 has an Intel i855GME 
> chipset.
> I thought I can use either est or ichss and ichss is better.
> Maybe I'm confused.

There were three versions of SpeedStep that are supported in -current. 
The oldest, SMI-based SS is present in 440bx parts and is supported by 
the smist driver.  The next oldest is system IO based SS, which is an 
evolution of smist and is supported by the ichss driver.  Both offer 
only two speeds, full speed and some lower rate (typically ~70% of full 
speed).  Both are supported by the chipset alone with no CPU 
interaction.  The newest, Pentium-M type SpeedStep, is accessed via MSRs 
and sometimes chipset-assisted system IO.  It offers multiple speeds and 
steps both voltage and clocks, saving much more power.  It is supported 
by the est driver.

Both ichss and est capabilities are sometimes exported by the BIOS 
through ACPI Px states, supported by the acpi_perf driver.  Enabling 
ACPI provides support for acpi_throttle and acpi_perf.  Enabling cpufreq 
enables support for smist, ichss, and est.  The OS should autoprobe and 
enable the best one supported by your system, in this order:
acpi_perf > est > ichss > smist

-- 
Nate