Created attachment 23543 [details]
output of acpidump

Since kernel 2.6.31.4 (previous 2.6.31 kernels did not boot) the cpufreq driver speedstep-ich compiled into the kernel does not work anymore on my notebook Compaq Presario 2800 (customer version of EVO N800c) with Pentium 4m CPU with 1900 MHz.
The directory cpufreq under /sys/devices/system/cpu/cpu0/ is missing and the CPU is running at a "fractal" frequency (1893.922 MHz).

I recompiled the kernel with the CPUFreq processor drivers "ACPI Processor
P-States" and "Intel Speedstep on ICH-M chipsets (ioport interface)" as modules.
I manually tried to insert the cpufreq driver modules, result:

# modprobe speedstep-ich
FATAL: Error inserting speedstep_ich
(/lib/modules/2.6.31.5/kernel/arch/x86/kernel/cpu/cpufreq/speedstep-ich.ko): No
such device
# modprobe -r speedstep-lib

# modprobe acpi-cpufreq

This driver works. the cpufreq entry in /sys/devices/system/cpu/cpu0/ exists
and, since I'm using the ondemand governor, the CPU frequency without load is
1200 MHz (my Compaq has a Pentium 4m 1900 MHz).

I attach the output of acpidump and dmesg, as well as my kernel config.

I already contacted Zhao Yakui from Intel who suggested to open this bug report.