Comment 167 for bug 1488719

I have been affected by this bug for a while as well. This is my setup:

Dell E5450 with Ubuntu 14.04.04 LTS with kernel: 4.2.0-34-generic

The laptop is connected to a Dell E-Port Plus Advanced Port Replicator.

The port replicator is connected via two seperate DP -> mDP cables to two monitors of model Dell 27" QHD U2715H.

I get the same annoying error in dmesg but that is the least of my problems. I also get complete crashes where changing TTY is impossible. The entire laptop will also at times reboot, even when not being used. I also get the same problem others have reported where waking up the laptop causes the second screen to go back into power-save mode. I used to have screen flickering in Windows 10 Professional. But i have not seen this behavior in Ubuntu.

I also get this suspicious error in /var/log/syslog

Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931613] ------------[ cut here ]------------
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931631] WARNING: CPU: 1 PID: 1367 at /build/linux-lts-wily-MVxxD8/linux-lts-wily-4.2.0/drivers/gpu/drm/i915/intel_ddi.c:756 intel_ddi_get_crtc_new_encoder+0x94/0xa0 [i915]()
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931632] 2 encoders on crtc for pipe A
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931633] Modules linked in: pci_stub vboxpci(OE) vboxnetadp(OE) vboxnetflt(OE) vboxdrv(OE) cmac dm_crypt dell_wmi sparse_keymap dell_laptop dcdbas dell_smm_hwmon hid_logitech_hidpp uvcvideo intel_rapl x86_pkg_temp_thermal intel_powerclamp coretemp videobuf2_vmalloc videobuf2_memops kvm_intel snd_soc_rt5640 videobuf2_core btusb btrtl btbcm v4l2_common btintel kvm videodev snd_soc_rl6231 media crct10dif_pclmul snd_soc_core crc32_pclmul bnep rfcomm snd_compress arc4 ac97_bus snd_pcm_dmaengine bluetooth snd_seq_midi aesni_intel aes_x86_64 iwlmvm lrw gf128mul glue_helper ablk_helper cryptd mac80211 snd_seq_midi_event snd_rawmidi dell_led iwlwifi snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic joydev input_leds snd_hda_intel snd_hda_codec cfg80211 serio_raw snd_seq mei_me snd_hda_core snd_hwdep mei lpc_ich shpchp snd_pcm snd_seq_device snd_timer dw_dmac snd dw_dmac_core int3403_thermal 8250_fintek snd_soc_sst_acpi dell_smo8800 parport_pc soundcore 8250_dw ppdev i2c_hid int3400_thermal spi_pxa2xx_platform processor_thermal_device acpi_thermal_rel acpi_pad dell_rbtn i2c_designware_platform intel_soc_dts_iosf i2c_designware_core mac_hid int3402_thermal acpi_als int340x_thermal_zone lp parport kfifo_buf industrialio hid_logitech_dj hid_generic usbhid hid i915 psmouse i2c_algo_bit ahci drm_kms_helper e1000e libahci drm ptp sdhci_pci pps_core wmi sdhci_acpi video sdhci
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931682] CPU: 1 PID: 1367 Comm: Xorg Tainted: G OE 4.2.0-34-generic #39~14.04.1-Ubuntu
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931683] Hardware name: Dell Inc. Latitude E5450/09X6YN, BIOS A10 09/01/2015
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931684] ffffffffc026b130 ffff8804085eb9c8 ffffffff817b5fed 0000000000000000
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931686] ffff8804085eba18 ffff8804085eba08 ffffffff8107799a 0000000100020101
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931687] ffff8800d5272500 ffff88040698a800 ffff880406c86f00 ffff8804061c8f78
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931688] Call Trace:
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931692] [<ffffffff817b5fed>] dump_stack+0x45/0x57
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931695] [<ffffffff8107799a>] warn_slowpath_common+0x8a/0xc0
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931697] [<ffffffff81077a16>] warn_slowpath_fmt+0x46/0x50
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931709] [<ffffffffc0221ce4>] intel_ddi_get_crtc_new_encoder+0x94/0xa0 [i915]
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931721] [<ffffffffc02222e5>] intel_ddi_pll_select+0x35/0xfe0 [i915]
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931732] [<ffffffffc020c63b>] ? intel_check_primary_plane+0xdb/0x330 [i915]
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931734] [<ffffffff811d0901>] ? __kmalloc_track_caller+0x1a1/0x250
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931745] [<ffffffffc020491a>] ? __intel_set_mode+0x11a/0xb10 [i915]
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931755] [<ffffffffc01f5c46>] haswell_crtc_compute_clock+0x16/0x40 [i915]
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931765] [<ffffffffc0204d9b>] __intel_set_mode+0x59b/0xb10 [i915]
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931775] [<ffffffffc0206592>] ? intel_modeset_compute_config+0x362/0xb60 [i915]
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931785] [<ffffffffc020be16>] intel_crtc_set_config+0x366/0x5a0 [i915]
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931794] [<ffffffffc0063428>] drm_mode_set_config_internal+0x68/0x100 [drm]
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931801] [<ffffffffc006734d>] drm_mode_setcrtc+0xdd/0x4f0 [drm]
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931806] [<ffffffffc0058733>] drm_ioctl+0x363/0x680 [drm]
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931812] [<ffffffffc0067270>] ? drm_mode_setplane+0x1c0/0x1c0 [drm]
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931815] [<ffffffff811fe2bd>] do_vfs_ioctl+0x2cd/0x4b0
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931817] [<ffffffff811edaf5>] ? __sb_end_write+0x35/0x70
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931818] [<ffffffff811eb7ec>] ? vfs_write+0x15c/0x190
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931820] [<ffffffff811fe519>] SyS_ioctl+0x79/0x90
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931821] [<ffffffff81200465>] ? SyS_poll+0x65/0xf0
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931823] [<ffffffff817bd3f2>] entry_SYSCALL_64_fastpath+0x16/0x75
Apr 12 08:53:43 SIKR-E5450 kernel: [ 5.931824] ---[ end trace 80cd1a97a7e511d3 ]---

If i can help in any way, please notifiy me.