Recently a 2011 15.4″ MacBook Pro was brought in with a damaged GPU. The machine would only boot into safe mode, which was not particularly helpful for normal use.since some drivers are automatically disabled. Cost of a replacement logic board was too high to make a repair worthwhile.
As it turns out, many 15″ MacBook Pros, Minis and some iMacs are equipped with both a discrete and integrated GPU. It is possible to disable the discrete (failing) GPU and restore an acceptable level of performance unless the machine is being used for heavy graphics-oriented applications.
After reading through and trying recommendations from a number of posts, I came across a procedure which was purely software configuration. After several tries, I was able to document the procedure into a series of repeatable steps. In most cases system updates would overwrite the changes and require the process to be repeated to restore operation.
The entire process requires booting into recovery and single-user mode and a fair bit of typing in Terminal mode but is quite rewarding when the system finally comes back to life. With the discrete GPU disabled, the system runs much cooler, which is an additional perk. The process can be summarized in six steps:
- Boot into alternate operating system (archLinux)
- Clear efivars and set a new value for gpu-power-prefs
- Reset SMC and PRAM
- Boot into Recovery mode and disable SIP
- Boot into single-user mode and disable GPU, enable Verbose mode
- Reboot to single-user mode, relocate the kext and update kextcache
- Reboot normally, load the relocated kext.