Created attachment 145332 [details]
Multiple instances of the Panic
iMac late 2011 with 2 Thunderbolt displays.
Kernel 5.2 finally got DP routing working to allow both TB displays to work, however I'm now getting lockups which appear to be triggered in radeon_dp_needs_link_train.
I'm capturing these over netconsole as it leaves the machine paralysed.
Attachment faults.txt has 4 separate instances of the fault from 4 different boots.
This machine stays on 24/7 and this seems to occur when the displays wake up after a dpms sleep. Having said that I've also seen the fault when doing something innocuous like changing the audio volume.
Generally at least 2 of the screens wakeup, so I have displays with a lockscreen asking for a password and a mouse, but the machine is dead.
The last example in faults.txt left the machine in a state where I could ssh in and reboot it. All the others required a hard power cycle.
I'm currently using 5.2.11. Previously I was using 4.17, but I can't roll back prior to 5.2 without losing the second TB display, and it can take hours or days to hit so bisection would be difficult.
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Blackcomb [Radeon HD 6970M/6990M] (prog-if 00 [VGA controller])
Subsystem: Apple Inc. Radeon HD 6970M
Flags: bus master, fast devsel, latency 0, IRQ 79
Memory at 90000000 (64-bit, prefetchable) [size=256M]
Memory at a8800000 (64-bit, non-prefetchable) [size=128K]
I/O ports at 2000 [size=256]
Expansion ROM at a8820000 [disabled] [size=128K]
Capabilities:  Power Management version 3
Capabilities:  Express Legacy Endpoint, MSI 00
Capabilities: [a0] MSI: Enable+ Count=1/1 Maskable- 64bit+
Capabilities:  Vendor Specific Information: ID=0001 Rev=1 Len=010 <?>
Capabilities:  Advanced Error Reporting
Kernel driver in use: radeon
Kernel modules: radeon
Created attachment 145333 [details]
Created attachment 145334 [details]