frozen graphics on wake from suspend with 4.15.0-0.rc1.git0.1.fc28.x86_64

This is a problem I haven't previously seen on this laptop. So far it won't reproduce with drm.debug, but I've seen it twice without. It can't be reported due to kernel taint resulting from i915.enable_guc_loading=1 i915.enable_guc_submission=1 which I can disable if it's helpful. [20016.975715] [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO underrun ... [24380.311647] [drm:intel_dp_aux_ch [i915]] *ERROR* dp aux hw did not signal timeout (has irq: 1)! [24383.411501] ------------[ cut here ]------------ [24383.411504] DC6 already programmed to be enabled. [24383.411694] WARNING: CPU: 2 PID: 5306 at drivers/gpu/drm/i915/intel_runtime_pm.c:609 skl_enable_dc6+0x9e/0xb0 [i915] Complete dmesg: https://drive.google.com/open?id=113a2TnnbVDcx9kM7hj9hCNgxLopGSIIG Complete journal: https://drive.google.com/open?id=1LuzQI2NZEC__KFjebzOtph_7X3q47VcJ 00:02.0 VGA compatible controller [0300]: Intel Corporation Skylake GT2 [HD Graphics 520] [8086:1916] (rev 07) (prog-if 00 [VGA controller]) -- Chris Murphy