kern/56724: Thinkpad x260 hard-hang during boot w/ i915drmkms

[thorpej%me.com@localhost]

>Number:         56724
>Category:       kern
>Synopsis:       Thinkpad x260 hard-hang during boot w/ i915drmkms
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Feb 19 17:55:00 +0000 2022
>Originator:     Jason Thorpe
>Release:        9.99.93 (sources updated Feb 19 2022 9am PST)
>Organization:
RISCy Business
>Environment:
NetBSD stinky 9.99.93 NetBSD 9.99.93 (GENERIC) #4: Sat Feb 19 09:23:05 PST 2022  thorpej@thorpej-m1-mbp.local:/opt/nbsd/src/sys/arch/amd64/compile/GENERIC amd64

>Description:
My Thinkpad x260 hard-hangs when booting unless i915drmkms is disabled.  Prior kernel from:

[     1.000000] NetBSD 9.99.92 (GENERIC) #37: Tue Oct 26 21:23:49 PDT 2021
[     1.000000]         thorpej@the-ripe-vessel:/space/src/sys/arch/amd64/compile/GENERIC

boots fine and reports the GPU as such:

[     1.015944] i915drmkms0 at pci0 dev 2 function 0: Intel HD Graphics 520 (GT2) (rev. 0x07)
.
.
.
[     3.184553] i915drmkms0: interrupting at msi6 vec 0 (i915drmkms0)
[     3.224553] kern error: [drm:(../../../../external/bsd/drm2/dist/drm/i915/intel_guc_loader.c:558)guc_fw_fetch] *ERROR* kern error: [drm:(../../../../external/bsd/drm2/dist/drm/i915/i915_drv.c:634)i915_firmware_load_error_print] *ERROR* failed to load firmware i915/skl_dmc_ver1.bin (0)
[     3.224553] Failed to fetch GuC firmware from i915/skl_guc_ver4.bin (error -2)
[     3.224553] kern error: [drm:(../../../../external/bsd/drm2/dist/drm/i915/i915_drv.c:646)i915_firmware_load_error_print] *ERROR* The driver is built-in, so to load the firmware you need to
[     3.315249] include it either in the kernel (see CONFIG_EXTRA_FIRMWARE) or
[     3.315249] in your initrd/initramfs image.
[     3.315249] kern error: [drm:(../../../../external/bsd/drm2/dist/drm/i915/i915_gem.c:5398)i915_gem_init_hw] *ERROR* Failed to initialize GuC, error -5 (ignored)
[     4.124557] intelfb0 at i915drmkms0
[     4.124557] intelfb0: framebuffer at 0xe0340000, size 1920x1080, depth 32, stride 7680

The hard-hang appears to happen after a fixed period of time.  That is to say:

- First attempt to boot hung after displaying "Waiting for duplicate address detection to complete."
- Second attempt hung after displaying "Starting postfix." after moving all of my tap and bridge interfaces.
- Third attempt hung after displaying "Building databases: dev, utmp" (never displayed "utmpx") with a LOCKDEBUG kernel.

I cannot drop into DDB using C-A-ESC when this happens, and the fans spin up to full speed in short order.

>How-To-Repeat:
Boot 9.99.93 with the new DRM on Thinkpad x260.
>Fix:
N/A