10.10.3 breaks support for ATI video cards

Question

The 10.10.3 update has broken support for a bunch of ATI video cards that worked just fine under 10.10.2. This is for my Mac Pro 5,1. Some folks also reported issues with breaking support for Nvidia cards, but have mentioned that the latest Nvidia beta drivers might work.
There is a thread that may be found here that has some details:
OS X 10.10.3 Update
and here (reverting back to 10.10.2 fixes things):
http://forums.macrumors.com/showthread.php?t=1864352
Specifically, my Visiontek Eyefinity 6 7750 stopped working, and another users Radeon 7770 stopped working.  Yet, the 7970 continues to work.  Reverting to the old ATI 5770 that came with the machine renders it usable. This is a problem as the 7750 only took a single slot, and the two 5770s eat up 3 slots so I can't use my USB 3 card, etc.
I remember this once happened before.  I think it was with the 10.9.2 update which borked a bunch of video cards that worked fine under 10.9.1, and then were again made to work just fine with the 10.9.3 update.
All the 'standard' fixes have been attempted.  Clean installs.  Fix permissions. Etc.
Not sure why apple would seemingly disable support for these cards, other than by accident, I assume, much like happened with the 10.9.2 update.
Also not sure if just copying the correct driver from 10.10.2 might solve the problem until Apple get's around to fixing the issue.  Has anyone tried?  Any suggestions would be appreciated.  Thanks!

Answer 1

Hi, i am using dual Cinema Display 30 and 23 with a HIS ATI 7750 1 GB on a Mac Pro 3.1. Post upgrade from 10.10.2 to 10.10.3 my display eded unusable blurry. Therefore I have tried to replace the 10.10.3 kext with the previous 10.10.2. But it did not work out as expected. I managed to get some video output but no acceleration at all. Therefore the system is unusable. Therefore i full downgraded to 10.10.2 now.
Never the less it might be a good starting point for someone to get acceleration running. This is what I did:
I have to set the nvram variable kext-dev-mode=1, but be warned this will allow any unsigned > .kext to load, including rootlets, malware, etc.
I did this in order to allow me to modify the kext if necessary and to ensure that if 10.10.2 kext might be locked that they still be loaded and the computer will not be prevented from boot.
sudo nvram boot-args="kext-dev-mode=1"
sudo shutdown -r now
Post this i copied from my other Mac running 10.10.2 the file /System/Library/Extensions/AMDRadeonX4000.kext to my Mac Pro 3.1 running 10.10.3 with no proper video output. Basically i copied all ATI related kext from one mac to the other.
copied  [MAC10.10.2]/System/Library/Extensions/ATI* ----> [MAC10.10.3]/System/Library/Extensions/ATI*
copied  [MAC10.10.2]/System/Library/Extensions/AMD* ----> [MAC10.10.3]/System/Library/Extensions/AMD*
someone needs to do a diff here to identify the file with is necessary the only one i found with a significant change seems to be AMDRadeonX4000.kext
I forced to rebuild kext cache manually
sudo touch /System/Library/Extensions
sudo kextcache -m /System/Library/Caches/com.apple.kext.caches/Startup/Extensions.mkext /System/Library/Extensions
And reboot!
sudo shutdown -r now
After the reboot I had  display output but no acceleration at all. Seeing the video out put made me happy but the system is unusable to to the lack of acceleration of the display. I am really looking forward for Apple to fix the update and to reapply support for the ATI GPUs hence it allows to save environmental resources to keep good products like the Mac Pro 3.1 running...