Since I use the kernel version 2.6.41.4-1 I got the following problem:

In the idle mode the governor set scaling_min_freq correctly to 800 Mhz, but anyway the CPU goes with 1600 Mhz. If I plug in the battery (even if the notebook is on the power supply) the frequency increases to 1700 Mhz.

If I boot with the old kernel 2.6.40.6-0, everything is fine.

# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies 
2001000 2000000 1900000 1800000 1700000 1600000 1500000 1400000 1300000 1200000 1100000 1000000 900000 800000
# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq 
800000
# cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq 
1600000

$ cat /proc/cpuinfo 
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 42
model name	: Intel(R) Core(TM) i7-2630QM CPU @ 2.00GHz
stepping	: 7
cpu MHz		: 800.000
cache size	: 6144 KB
physical id	: 0
siblings	: 8
core id		: 0
cpu cores	: 4
apicid		: 0
initial apicid	: 0
fpu		: yes
fpu_exception	: yes
cpuid level	: 13
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm sse4_1 sse4_2 x2apic popcnt aes xsave avx lahf_lm ida arat epb xsaveopt pln pts dts tpr_shadow vnmi flexpriority ept vpid
bogomips	: 3991.11
clflush size	: 64
cache_alignment	: 64
address sizes	: 36 bits physical, 48 bits virtual
power management:

[...] (same output for all the other 7 cores)


My Notebook: XPS 15 (Dell) with the latest bios version (A07)