Apple T2 AMD GPU issue with kernel parameter fix to add to known issues page for MacBookPro16,1 compatibility
Hi team,
I continue to test Tails on my MacBookPro16,1 and have an important compatibility fix to report which I assume would belong on the known issues page.
The issue: With default Tails kernel parameters, Tails will very regularly and easily cause an iBridge panic (the issue where the Mac can suddenly freeze, screen goes black, fan quickly blows out at top speed, and machine shuts down).
The fix: Add amdgpu.dpm=0
to kernel parameters.
The explanation I can provide:
The parameter disables 'dynamic power management' for the AMD dGPU. It's a crude fix, that works, for what is thought to be an Apple-fixable bug in UEFI firmware which is not (yet) patched at the lower level by Apple. It's thought that with dynamic power management on the dGPU can pull too much power or scale to an invalid voltage in terms of what the Intel chipset (PCH) expects. So, at the expense of potentially battery life optimisation, this fix may be needed to make Tails usable at all. (Offline or not.)
The issue probably affects all T2-chip battery-powered Macs with a discrete AMD GPU - potentially even desktop Macs too (if they happen to apply power management).
I tested the difference for weeks in both cases (no parameter = constant crashes, Tails unusable; add parameter = not a single crash since adding amdgpu.dpm=0
, with very extensive testing of Tails 4.19 using Internet on MacBookPro16,1 every day). Reliable fix.