Created attachment 120412 [details]
Xorg log

Using:

- xorg-server-1.17.2
- mesa 11.0.5
- xf86-video-intel 0340718366d7cb168a46930eb7be22f2d88354d8 (2015-11-14)

Problem:

1) I switch to external monitor with $ xrandr --output $mon_ext --mode 3440x1440 --output $mon_lap --off 

2) After some inactivity monitor goes to sleep

3) Monitor doesn't wake up, I have to switch back to laptop monitor first and then back to external

4) I can observe following kernel crash

[67338.581551] WARNING: CPU: 0 PID: 999 at /tmp/nix-build-linux-4.2.6.drv-0/linux-4.2.6/drivers/gpu/drm/i915/intel_dp.c:143 intel_dp_max_link_bw.isra.9+0x31/0x50 [i915]()
[67338.581553] invalid max DP link bw val 0, using 1.62Gbps
[67338.581555] Modules linked in: ansi_cprng drbg ctr ccm fuse af_packet cmac rfcomm bnep ext2 mbcache snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic uvcvideo btusb btrtl iwlmvm btbcm cdc_mbim btintel videobuf2_vmalloc mac80211 bluetooth cdc_wdm videobuf2_memops videobuf2_core cdc_ncm v4l2_common usbnet crc16 videodev cdc_a
cm mii crc32_pclmul joydev mousedev coretemp snd_pcm_oss i915 snd_mixer_oss intel_gtt arc4 drm_kms_helper evdev crct10dif_pclmul input_leds iwlwifi ecb drm intel_powerclamp x86_pkg_temp_thermal snd_hda_intel mac_hid agpgart serio_raw psmouse snd_hda_codec i2c_algo_bit cfg80211 mei_me i2c_core thermal mei snd_hda_core e1000e wmi snd_hwdep t
pm_tis snd_pcm battery lpc_ich snd_timer tpm ac shpchp ptp button ppp_mppe pps_core ppp_generic slhc processor loop cpufreq_ondemand
[67338.581626]  vboxnetflt(O) vboxnetadp(O) vboxdrv(O) uinput thinkpad_acpi nvram video thermal_sys snd soundcore rfkill kvm_intel kvm ipv6 autofs4 atkbd libps2 aesni_intel aes_x86_64 lrw gf128mul glue_helper ablk_helper cryptd sd_mod xhci_pci rtc_cmos i8042 serio unix crc32c_generic crc32c_intel btrfs zlib_deflate xor raid6_pq hid_lenovo 
led_class ums_realtek usb_storage hid_generic ohci_hcd usbhid hid uhci_hcd ahci libahci libata scsi_mod ehci_pci ehci_hcd xhci_hcd usbcore usb_common dm_crypt dm_mod
[67338.581671] CPU: 0 PID: 999 Comm: X Tainted: G        W  O    4.2.6 #1-NixOS
[67338.581672] Hardware name: LENOVO 20BS006BSC/20BS006BSC, BIOS N14ET25W (1.03 ) 12/01/2014
[67338.581674]  ffffffffa0bc58a0 ffff8800b1d3f9e8 ffffffff814bd7a1 0000000000000007
[67338.581676]  ffff8800b1d3fa38 ffff8800b1d3fa28 ffffffff8106a2da 0000000000000000
[67338.581678]  0000000000000000 ffffffffa0baf068 ffff88021eafb800 ffff8800b1d3fb18
[67338.581680] Call Trace:
[67338.581691]  [<ffffffff814bd7a1>] dump_stack+0x45/0x57
[67338.581699]  [<ffffffff8106a2da>] warn_slowpath_common+0x8a/0xc0
[67338.581700]  [<ffffffff8106a356>] warn_slowpath_fmt+0x46/0x50
[67338.581721]  [<ffffffffa0b815b1>] intel_dp_max_link_bw.isra.9+0x31/0x50 [i915]
[67338.581731]  [<ffffffffa0b82d82>] intel_dp_common_rates+0xe2/0xf0 [i915]
[67338.581739]  [<ffffffffa0b85f3b>] intel_dp_compute_config+0xbb/0x7a0 [i915]
[67338.581747]  [<ffffffffa0b7bd76>] intel_ddi_compute_config+0x56/0xa0 [i915]
[67338.581755]  [<ffffffffa0b61315>] intel_modeset_compute_config+0x325/0xb10 [i915]
[67338.581770]  [<ffffffffa0a2a58d>] ? drm_atomic_set_fb_for_plane+0x2d/0x90 [drm]
[67338.581780]  [<ffffffffa0b66d02>] intel_crtc_set_config+0x2a2/0x590 [i915]
[67338.581783]  [<ffffffff814c1096>] ? mutex_lock+0x16/0x40
[67338.581789]  [<ffffffffa0a19e56>] drm_mode_set_config_internal+0x66/0x100 [drm]
[67338.581795]  [<ffffffffa0a1e219>] drm_mode_setcrtc+0x189/0x4d0 [drm]
[67338.581798]  [<ffffffffa0a0f405>] drm_ioctl+0x1a5/0x650 [drm]
[67338.581803]  [<ffffffff811c010a>] do_vfs_ioctl+0x2ba/0x490
[67338.581808]  [<ffffffff810f7641>] ? __audit_syscall_entry+0xb1/0x100
[67338.581811]  [<ffffffff81020a86>] ? do_audit_syscall_entry+0x66/0x70
[67338.581813]  [<ffffffff811c0359>] SyS_ioctl+0x79/0x90
[67338.581815]  [<ffffffff81022093>] ? syscall_trace_leave+0x93/0xf0
[67338.581817]  [<ffffffff814c2f2e>] entry_SYSCALL_64_fastpath+0x12/0x71
[67338.581818] ---[ end trace 062bde697e5e3513 ]---


xrandr output when external monitor is active

Screen 0: minimum 8 x 8, current 3440 x 1440, maximum 32767 x 32767
eDP1 connected (normal left inverted right x axis y axis)
   2560x1440     60.00 +
   1920x1440     60.00  
   1856x1392     60.01  
   1792x1344     60.01  
   2048x1152     60.00  
   1920x1080     60.00  
   1600x1200     60.00  
   1400x1050     59.98  
   1600x900      60.00  
   1280x1024     60.02  
   1280x960      60.00  
   1368x768      60.00  
   1280x720      60.00  
   1024x768      60.00  
   1024x576      60.00  
   960x540       60.00  
   800x600       60.32    56.25  
   864x486       60.00  
   640x480       59.94  
   720x405       60.00  
   640x360       60.00  
DP1 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
HDMI2 connected 3440x1440+0+0 (normal left inverted right x axis y axis) 800mm x 335mm
   3440x1440     49.99*+  29.99  
   2560x1080     60.00  
   1920x1080     60.00    60.00    59.94  
   1680x1050     59.88  
   1600x900      60.00  
   1280x1024     60.02  
   1280x800      59.91  
   1152x864      59.97  
   1280x720      60.00    59.94  
   1024x768      60.00  
   800x600       60.32  
   720x480       60.00    59.94  
   640x480       60.00    59.94  
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

$ uname -a
Linux guava 4.2.6 #1-NixOS SMP Thu Jan 1 00:00:01 UTC 1970 x86_64 GNU/Linux

Using HDMI as connector.