Broadwell IGPU alway above 500MHz (P-States>=10)

[virgosun]

I follow native power management guide and my rig seem stable and have all state.

Minimum speed for IGPU is reported 300MHz but in fact it never run below 500MHz, even on ideal.
Any idea?
Thank you

CPU Ratio Info:
------------------------------------
CPU Low Frequency Mode.............: 500 MHz
CPU Maximum non-Turbo Frequency....: 2200 MHz
CPU Maximum Turbo Frequency........: 2200 MHz

IGPU Info:
------------------------------------
IGPU Current Frequency.............:  500 MHz
IGPU Minimum Frequency.............:  300 MHz
IGPU Maximum Non-Turbo Frequency...:  300 MHz
IGPU Maximum Turbo Frequency.......:  900 MHz
IGPU Maximum limit.................: No Limit

CPU P-States [ (13) 18 22 ] iGPU P-States [ (10) ]
CPU C3-Cores [ 0 1 2 3 ]
CPU C6-Cores [ 0 1 2 3 ]
CPU C7-Cores [ 0 1 2 3 ]
CPU P-States [ (13) 15 18 22 ] iGPU P-States [ (10) ]
CPU P-States [ 13 15 18 19 (22) ] iGPU P-States [ (10) ]
CPU P-States [ (13) 15 16 18 19 22 ] iGPU P-States [ (10) ]
CPU P-States [ (13) 15 16 17 18 19 22 ] iGPU P-States [ (10) ]
CPU P-States [ (13) 14 15 16 17 18 19 22 ] iGPU P-States [ (10) ]
CPU P-States [ (13) 14 15 16 17 18 19 20 22 ] iGPU P-States [ (10) ]
CPU P-States [ (13) 14 15 16 17 18 19 20 22 ] iGPU P-States [ 10 (13) ]
CPU P-States [ (13) 14 15 16 17 18 19 20 22 ] iGPU P-States [ 10 (11) 13 ]
CPU P-States [ (13) 14 15 16 17 18 19 20 22 ] iGPU P-States [ 10 11 13 (15) ]
CPU P-States [ (13) 14 15 16 17 18 19 20 22 ] iGPU P-States [ 10 11 13 15 (17) ]
CPU P-States [ (13) 14 15 16 17 18 19 20 22 ] iGPU P-States [ 10 11 13 15 (16) 17 ]
CPU P-States [ 13 14 15 16 17 18 19 20 (22) ] iGPU P-States [ 10 11 (12) 13 15 16 17 ]
CPU P-States [ 13 14 15 16 17 18 19 20 (22) ] iGPU P-States [ 10 11 12 13 (14) 15 16 17 ]
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