Running 3.10-rc7 on an i5-4200U, with either intel_pstate or the older cpufreq drivers the CPU was stuck at 800MHz. I added the model, 0x45, to intel_pstate_cpu_ids and frequency scaling seems to be working as intended now.
If this is already solved why not send a patch to dirk and list. And we can get it in quickly. Maybe for 3.11, before Rafael sends a pull request. :)
Patch sent to mailing list:
Author: Nell Hardcastle <email@example.com>
Date: Sun Jun 30 15:58:57 2013 -0700
intel_pstate: Add Haswell CPU models