Comment 25 for bug 1722536

[ 2.412673] drm: loading out-of-tree module taints kernel.
[ 2.412889] drm: module verification failed: signature and/or required key missing - tainting kernel
...
[ 2.445205] i915: Unknown symbol drm_mm_init_scan_with_range (err 0)
[ 2.445267] i915: Unknown symbol drm_kms_helper_poll_enable_locked (err 0)
[ 2.445327] i915: Unknown symbol drm_crtc_get_hv_timing (err 0)
[ 2.445574] i915: Unknown symbol drm_mm_init_scan (err 0)
[ 2.445627] i915: Unknown symbol drm_mm_insert_node_in_range_generic (err 0)

Seems like you were loading out-of-tree i915.

What's the output of `modinfo i915`?