I have tested the cpufreq-set -f 400MHz command for several kernels in Debian 9, and here is the result:
Kernels 4.9.0-3 to 4.9.0-5: CPU scaling is OK (but hibernation fails)
Kernels 4.13.0-0 CPU scaling fails to achieve constant lowest frequency available (but hibernation seems to work).
So it seems the bug in the CPU frequency scaling was introducing after 4.9.0-5 and before 4.13.0-0
I don't know how to test any kernel between those two because they are not in Backports. I am willing to test them if you could provide any link where I can find instructions on how to get those kernels.
Thanks.
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Eduardo Guerras Valera
Homer L. Dodge Department of Physics and Astronomy
440 W. Brooks St. - Norman, OK 73019-0225 - USA
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