Fixing a MacBook Pro 8,2 with dead AMD GPU
I've owned a MacBook Pro 8,2 late 2011 edition, which I used from 2011 to about 2018. It was a great piece of hardware, and honestly I'm surprised it lasted so long given how many MacOS and Fedora installs it's seen.
I upgraded to a MacBook Pro 15,1, and I gave the 8,2 to a friend who was in need of a new computer so she could do her work. It worked really well for her until today when she's messaged me that the machine is having a problem.
The machine appeared to be in a bootloop, where just before swapping from the EFI GPU to the main display server, it would go black and then lock up/reboot. Booting to single user mode (boot holding cmd + s) showed the machine's disk was intact with a clean apfs. The system.log showed corruption at the time of the fault, which didn't instill confidence in me.
Attempting a recovery boot (boot holding cmd + r), this also yielded the bootloop. So we have potentially eliminated the installed copy of MacOS as the source of the issue.
I've then used the apple hardware test (boot while holding d), and it has passed the machine as a clear bill of health.
I have seen one of these machines give up in the past - my friends mother had one from the same generation and that died in almost the same way - could it be the same?
The 8,2's cursed gpu stack
The 8,2 15" mbp has dual gpu's - it has the on cpu Intel 3000, and an AMD radeon 6750M. The two pass through an LVDS graphics multiplexer to the main panel. The external display port however is not so clear - the DDC lines are passed through the GMUX, but the datalines directly attach to the the display port.
The machine is also able to boot with EFI rendering to either card. By default this is the AMD radeon. Which ever card is used at boot is also the first card MacOS attempts to use, but it will try to swap to the radeon later on.
This generation had a large number of the radeons develop faults in their 3d rendering capability so it would render the EFI buffer correctly, but on the initiation of 3d rendering it would fail. Sounds like what we have here!
To fix this ...
Okay, so this is fixable. First, we need to tell EFI to boot primarily from the intel card. Boot to single user mode and then run.
Now we need to prevent loading of the AMD drivers so that during the boot MacOS doesn't attempt to swap from Intel to the Radeon. We can do this by hiding the drivers. System integrity protection will stop you, so you need to do this as part of recovery. Boot with cmd + r, which now works thanks to the EFI changes, then open terminal
cd /Volumes/Macintosh HD
sudo mkdir amdkext
sudo mv System/Library/Extensions/AMDRadeonX3000.kext amdkext/
Then reboot. You'll notice the fans go crazy because the Radeon card can't be disabled without the driver. We can post-boot load the driver to stop the fans to fix this up.
To achieve this we make a helper script:
# cat /usr/local/libexec/amd_kext_load.sh
And a launchctl daemon
# cat /Library/LaunchDaemons/au.net.blackhats.fy.amdkext.plist
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
Now if you reboot, you'll have a working mac, and the fans will stop properly. I've tested this with suspend and resume too and it works! The old beast continues to live :)