Comment # 111 on bug 81644 from Alex Deucher

(In reply to comment #110)
> I found this post, stating some of the ASUS hardware comes PRE-OVERCLOCKED
> from the factory. Good chance this is the cause of my instability?
> 
> http://www.tomshardware.com/answers/id-2041324/problem-asus-270x-screen-
> blank-game.html
> 
> My GPU:
> 
> http://www.newegg.com/Product/Product.aspx?Item=N82E16814121802&nm_mc=KNC-
> GoogleAdwords&cm_mmc=KNC-GoogleAdwords-_-pla-_-Desktop+Graphics+Cards-_-
> N82E16814121802&gclid=COjjs6v3_MACFRAR7Aod_2EAqQ
> 
> Core clock is listed at 1120 Mhz, not 1050 Mhz.

Radeon already limits the clocks in certain cases depending on the vbios
tables.  You can disable dpm which will keep the chip at the default boot up
levels (usually some where in the range of 300e/150m) for testing.  Append
radeon.dpm=0 to the kernel command line in grub.