[Intel-gfx] Feature request: ability to change Core Render Clock for performance or battery life

Nando nando4eva at gmail.com
Fri Jun 5 08:29:50 CEST 2009

Hi Intel Gfx developers,

I would like the  to request a feature to the intel-gfx driver to be able to
change the Core Render Clock on the GM965 chipset, in the same way that ATI
Powerplay can, in order to increase performance or improve battery life.
(eg: 9.5W versus 13.5W TDP).

The chipset's datasheet tells us this can be done, and I've documented what
I know here <http://forum.notebookreview.com/showthread.php?p=4907993>. It
would be useful also to know what the sequence is to do this under Windows
type environments.  I've attachd some notes of the bits that might be
relevant from the datasheet. Perhaps an Intel developer can explain the
sequence to disable the link, change the registers relating to Core Render
Clock, then enable the link within a live running system? I could do this
using BarEdit in Windows.

Your assistance greatly appreciated.

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1/ Enable 0/1/0 device to control Link
0/0/0/PCI 54-57h
Bit 1 PCI Express Graphics Port Enable (D1EN)
0 = disable and hide 0/1/0
1 = enable and show 0/1/0

< do a scan in Device Manager and the device it finds a new device 0/1/0/PCI

2/ Disable Link/device
0/1/0/PCI B0-B1h
Bit 4 Link Disable
0 = Normal operation
1 = Link is disabled. Link retraining happens automatically on 0 to 1 transition

3/ Disable/powerdown graphics?
Device 0/2/0 D4-D5h
Bit 1:0 Power State
On a transition from D3 to D0 the graphics controller is optionally reset to initial values

00 = D0 Default
11 = D3 

Device 0/2/0 C0h
Bit 0: Graphics Debug Reset
0 = Deassert display and render domain reset
1 = Assert display and render domain reset 
Device 2 Config registers are available when Graphics debug reset is asserted

0/0/0/PCI 54-57h
Bit 4 Internal Graphics Engine Function (D2F1EN)
0 = disable and hide 0/2/1
1 = enable and show 0/2/1

Bit 3 Internal Graphics Engine Function (D2F1EN)
0 = disable and hide 0/2/0
1 = enable and show 0/2/0

4/ Enable faster for performance, slower for battery life Core Render Clock
Device 0/2/0  F0-F1h
Bits 12:8 Graphics Core Render Clock select:
00010 - 320/333Mhz <--- default on my system

Bits 3:0 Core Render clock select
0010 = 250/267 <---- tried this for better battery life -> seems the same
0011 = 320/333
0100 = 400/444 <--- default on my system
0101 = 500/533 <--- tried this for better performance -> seems the same

5/ Reverse steps 1-3 to bring up device/link up

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