[PATCH] drm/radeon: disable dpm on rv770 by default

[Andy Furniss]

Alex Deucher wrote:
> There seem to be stability issues on a number of cards.
>
> bugs: https://bugs.freedesktop.org/show_bug.cgi?id=76286
> https://bugzilla.redhat.com/show_bug.cgi?id=1085785
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=741619

Well TBH I don't know whether the following is useful info or not - it
could just be an unrelated waste of your time.

I have run my 4890 with dpm=1 from when it first appeared without issue
till recently.

As in the bug above I can't now use two screens - but the thing is,  I
use a (getting old) LFS, I don't use the TV that much, but when I
noticed the issue I tried to bisect and I reached the commit after my
working start point.

It turned out that my working was the last kernel I compiled with GCC
4.6.3. I had upgraded to GCC 4.8.2 and no kernel built with that can
handle 2 screens without locking, no sysrq, no network but very rarely
may unlock for a short while (did a dmesg when this happened, nothing
unusual logged then it locked again).

I built my GCC 4.6.3 again and built the same recent kernel (I run drm 
next or
fixes) and I have so far not been able to lock it with 2 screens.

Of course it could just be something on my LFS is too old for recent
GCC, or because I don't use TV much I am being lucky with 4.6.3.

I will when I get time build 4.8.2 again and see if dpm=0 works for me.