[Bug 105962] [KBL] "enable_rc6" parameter deprecation brings back freezing

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=105962

--- Comment #43 from Arthur <aeigenbrot at gmail.com> ---
Hi Jani,

Thanks for your response. I tried your suggestion on kernel 4.18.5 and
confirmed that DMC firmware was not loaded:

$ dmesg | grep i915
[    0.000000] Command line: BOOT_IMAGE=/vmlinuz-linux root=UUID=XXX rw quiet
i915.dmc_firmware_path=
[    0.000000] Kernel command line: BOOT_IMAGE=/vmlinuz-linux root=UUID=XXX rw
quiet i915.dmc_firmware_path=
[    1.949621] i915 0000:00:02.0: enabling device (0006 -> 0007)
[    1.953115] i915 0000:00:02.0: vgaarb: changed VGA decodes:
olddecodes=io+mem,decodes=io+mem:owns=mem
[    1.953356] i915 0000:00:02.0: Failed to load DMC firmware . Disabling
runtime power management.
[    1.953359] i915 0000:00:02.0: DMC firmware homepage:
https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/tree/i915
[    1.999251] [drm] Initialized i915 1.6.0 20180514 for 0000:00:02.0 on minor
0
[    2.004006] snd_hda_intel 0000:00:1f.3: bound 0000:00:02.0 (ops
i915_audio_component_bind_ops [i915])
[    3.226906] i915 0000:00:02.0: fb0: inteldrmfb frame buffer device

In this state I observed the following:

o With no peripherals plugged into my laptop I did not experience any immediate
crashes (which I would have expected if the problem persisted). This is good
news :)

o I then tried attaching a Thunderbolt 3 dock that, among other things,
connects an external monitor. Less than a minute later the system crashed. The
same thing happened if I booted the computer with the dock already connected.

o Just to test I then tried a boot with no dock and without turning off DMC
firmware (i.e., vanilla 4.18.5). This resulted in a crash.

So, it seems like the DMC firmware suggestion does make a real difference in
the absence of a dock/external monitor. Journalctl shows no strange behavior
before the dock'ed crashes (just like before), but over the next day or so I'll
try it again with either Kdump or PSTORE EFI to capture something. Previous
experience has not made me hopeful in this regard.

Thanks,
Arthur

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