Description of problem:
Seems to be associated with suspend/resume, but definitely not with every suspend/resume, and not with every undock-associated suspend.

I note the following from dmesg:

[23503.311697] [drm] Wrong MCH_SSKPD value: 0x16040307
[23503.311698] [drm] This can cause pipe underruns and display issues.
[23503.311698] [drm] Please upgrade your BIOS to fix this.

I don't know whether this is related. This is an X220 currently at the (very old) 1.12 BIOS level.

Additional info:
reporter:       libreport-2.1.9
WARNING: CPU: 3 PID: 687 at drivers/gpu/drm/i915/intel_pm.c:5452 __gen6_gt_wait_for_fifo+0x7e/0x90 [i915]()
Modules linked in: tun usb_storage fuse bnep bluetooth nf_conntrack_netbios_ns nf_conntrack_broadcast ipt_MASQUERADE ip6t_REJECT xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw input_polldev snd_hda_codec_hdmi snd_hda_codec_conexant arc4 iwldvm mac80211 e1000e iTCO_wdt snd_hda_intel iwlwifi snd_hda_codec snd_hwdep snd_seq snd_seq_device snd_pcm sdhci_pci snd_page_alloc snd_timer i915 uvcvideo videobuf2_vmalloc videobuf2_memops videobuf2_core videodev thinkpad_acpi media x86_pkg_temp_thermal iTCO_vendor_support mei_me sdhci mei mmc_core lpc_ich cfg80211 ptp snd coretemp kvm_intel kvm crc32_pclmul crc32c_intel ghash_clmulni_intel pps_core shpchp microcode wmi mfd_core joydev serio_raw i2c_algo_bit drm_kms_helper drm i2c_i801 i2c_core rfkill soundcore mperf video tpm_tis tpm tpm_bios nfsd auth_rpcgss nfs_acl lockd sunrpc dm_crypt
CPU: 3 PID: 687 Comm: X Not tainted 3.11.7-300.fc20.x86_64 #1
Hardware name: LENOVO 4291WAH/4291WAH, BIOS 8DET42WW (1.12 ) 04/01/2011
 0000000000000009 ffff880230675aa8 ffffffff8164350b 0000000000000000
 ffff880230675ae0 ffffffff8106715d 0000000000000000 00000000ffffffff
 ffff880231334000 0000000000000206 00000000ffffffff ffff880230675af0
Call Trace:
 [<ffffffff8164350b>] dump_stack+0x45/0x56
 [<ffffffff8106715d>] warn_slowpath_common+0x7d/0xa0
 [<ffffffff8106723a>] warn_slowpath_null+0x1a/0x20
 [<ffffffffa03f3dde>] __gen6_gt_wait_for_fifo+0x7e/0x90 [i915]
 [<ffffffffa03a13fd>] i915_write32+0x12d/0x150 [i915]
 [<ffffffffa03f8b25>] gen6_ring_put_irq+0x75/0xe0 [i915]
 [<ffffffffa03b3a93>] __wait_seqno+0x393/0x520 [i915]
 [<ffffffff81089410>] ? wake_up_atomic_t+0x30/0x30
 [<ffffffffa03b49c0>] i915_wait_seqno+0x70/0xa0 [i915]
 [<ffffffffa03b4efa>] i915_gem_object_wait_rendering+0x4a/0x80 [i915]
 [<ffffffffa03b6357>] i915_gem_object_set_to_gtt_domain+0x47/0x160 [i915]
 [<ffffffffa03b7cd7>] i915_gem_pwrite_ioctl+0x287/0x860 [i915]
 [<ffffffff81075483>] ? __sigqueue_free.part.15+0x33/0x40
 [<ffffffff81075c92>] ? dequeue_signal+0x32/0x160
 [<ffffffffa011e142>] drm_ioctl+0x532/0x660 [drm]
 [<ffffffff81078c5c>] ? signal_setup_done+0x3c/0x60
 [<ffffffff81012575>] ? do_signal+0x195/0x5e0
 [<ffffffff8101cab7>] ? __restore_xstate_sig+0x87/0x500
 [<ffffffff811b9e7d>] do_vfs_ioctl+0x2dd/0x4b0
 [<ffffffff811ba0d1>] SyS_ioctl+0x81/0xa0
 [<ffffffff81652719>] system_call_fastpath+0x16/0x1b