drm hang on Sandy Bridge

[Kevin Oberman]

I have recently had two display hangs on my Sandy Bridge system running
drm-fbsd12.0-kmod-4.16.g20190430,  libdrm-2.4.97,1, and mesa-dri-19.0.0_3.
(Note the versions as some are not committed to ports at this time.)

The first occurred when attempting to resume from suspend and the second
was during normal use. Similar error in the log:
[drm] GPU HANG: ecode 6:0:0x7ffbfff9, in Xorg [100468], reason: Hang on
rcs0, action: reset
drmn0: Resetting chip after gpu hang
drmn0: Resetting chip after gpu hang
drmn0: i915_reset_device timed out, cancelling all in-flight rendering.

The following came after an attempt to unload i915kms and is probably not
surprising. System panic followed.
Warning: memory type drm_driver leaked memory on destroy (3 allocations, 64
bytes leaked).
Warning: memory type drm_kms leaked memory on destroy (2 allocations, 1088
bytes leaked).
--
Kevin Oberman, Part time kid herder and retired Network Engineer
E-mail: rkoberman at gmail.com
PGP Fingerprint: D03FB98AFA78E3B78C1694B318AB39EF1B055683