Comment 2 for bug 1597267

Note that compared to #1559308 , connecting the same monitor via the HDMI port on the laptop running 4.4.0-28-generic does seem to work fine:

There's still some stuff in dmesg when using HDMI as well:

snd_hda_codec_hdmi hdaudioC0D2: HDMI: ELD buf size is 0, force 128
snd_hda_codec_hdmi hdaudioC0D2: HDMI: invalid ELD data byte 0
------------[ cut here ]------------
WARNING: CPU: 1 PID: 1080 at /build/linux-BvkamA/linux-4.4.0/ubuntu/i915/intel_pm.c:3586 skl_update_other_pipe_wm+0x16c/0x180 [i915_bpo]()
WARN_ON(!wm_changed)
Modules linked in:
 ctr ccm rfcomm bnep arc4 snd_soc_skl snd_soc_skl_ipc snd_hda_ext_core intel_rapl x86_pkg_temp_thermal snd_soc_sst_ipc intel_powerclamp coretemp snd_soc_sst_dsp snd_hda_codec_hdmi snd_soc_core kvm_intel snd_compress ac97_bus snd_pcm_dmaengine snd_hda_codec_realtek kvm dw_dmac_core snd_hda_codec_generic input_leds snd_hda_intel irqbypass iwlmvm uvcvideo snd_hda_codec videobuf2_vmalloc videobuf2_memops mac80211 snd_hda_core videobuf2_v4l2 videobuf2_core v4l2_common snd_hwdep joydev serio_raw snd_pcm videodev btusb media btrtl thinkpad_acpi cdc_ether btbcm option iwlwifi nvram usbnet usb_wwan usbserial btintel mii rtsx_pci_ms snd_seq_midi bluetooth memstick snd_seq_midi_event cfg80211 snd_rawmidi mei_me mei snd_seq shpchp snd_seq_device snd_timer snd soundcore mac_hid parport_pc ppdev lp
 parport autofs4 btrfs xor raid6_pq drbg ansi_cprng algif_skcipher af_alg dm_crypt rtsx_pci_sdmmc i915_bpo crct10dif_pclmul crc32_pclmul aesni_intel intel_ips i2c_algo_bit aes_x86_64 drm_kms_helper lrw gf128mul glue_helper ablk_helper syscopyarea cryptd sysfillrect sysimgblt fb_sys_fops e1000e ahci drm psmouse ptp rtsx_pci pps_core libahci wmi video fjes
CPU: 1 PID: 1080 Comm: Xorg Not tainted 4.4.0-28-generic #47-Ubuntu
Hardware name: LENOVO 20F6007RGE/20F6007RGE, BIOS R02ET48W (1.21 ) 06/01/2016
 0000000000000286 000000009c6cf672 ffff88040dfa39a8 ffffffff813eb1a3
 ffff88040dfa39f0 ffffffffc0373c98 ffff88040dfa39e0 ffffffff81081102
 ffff88040fc7c000 ffff880409629d9c ffff88040fc7b000 ffff880409020b78
Call Trace:
 [<ffffffff813eb1a3>] dump_stack+0x63/0x90
 [<ffffffff81081102>] warn_slowpath_common+0x82/0xc0
 [<ffffffff8108119c>] warn_slowpath_fmt+0x5c/0x80
 [<ffffffffc02a569c>] skl_update_other_pipe_wm+0x16c/0x180 [i915_bpo]
 [<ffffffffc02a5836>] skl_update_wm+0x186/0x5f0 [i915_bpo]
 [<ffffffffc02b1800>] ? intel_display_power_put+0xd0/0x130 [i915_bpo]
 [<ffffffffc02a955e>] intel_update_watermarks+0x1e/0x30 [i915_bpo]
 [<ffffffffc0311db5>] intel_atomic_commit+0x485/0xdc0 [i915_bpo]
 [<ffffffffc00a47de>] ? drm_atomic_check_only+0x18e/0x590 [drm]
 [<ffffffffc00a4c17>] drm_atomic_commit+0x37/0x60 [drm]
 [<ffffffffc01a4b16>] drm_atomic_helper_set_config+0x76/0xb0 [drm_kms_helper]
 [<ffffffffc00a34aa>] ? drm_modeset_lock_all_ctx+0x9a/0xb0 [drm]
 [<ffffffffc0093e42>] drm_mode_set_config_internal+0x62/0x100 [drm]
 [<ffffffffc0098362>] drm_mode_setcrtc+0x3d2/0x4f0 [drm]
 [<ffffffffc0089742>] drm_ioctl+0x152/0x540 [drm]
 [<ffffffffc0097f90>] ? drm_mode_setplane+0x1b0/0x1b0 [drm]
 [<ffffffff81220b6f>] do_vfs_ioctl+0x29f/0x490
 [<ffffffff81701610>] ? __sys_recvmsg+0x80/0x90
 [<ffffffff81220dd9>] SyS_ioctl+0x79/0x90
 [<ffffffff818276b2>] entry_SYSCALL_64_fastpath+0x16/0x71
---[ end trace a13f8ffdea74aa69 ]---