Comment 6 for bug 1580272

I've also tested this on 4.4.0-22 with i915 patches here:
http://koti.kapsi.fi/~tjaalton/skl/mst/
And the problem persists.

In addition I've tested a 4.6 mainline from 5/8 and the problem persists there as well.

Here is the warning from the mainline kernel:
[ 44.871672] ------------[ cut here ]------------
[ 44.871687] WARNING: CPU: 1 PID: 871 at /home/kernel/COD/linux/drivers/gpu/drm/i915/intel_pm.c:3586 skl_update_other_pipe_wm+0x16c/0x180 [i915]
[ 44.871688] WARN_ON(!wm_changed)
[ 44.871688] Modules linked in:
[ 44.871689] rfcomm bnep snd_hda_codec_hdmi dell_led brcmfmac snd_hda_codec_realtek intel_rapl snd_hda_codec_generic x86_pkg_temp_thermal intel_powerclamp brcmutil coretemp uvcvideo cfg80211 i2c_designware_platform i2c_designware_core kvm_intel videobuf2_vmalloc kvm snd_hda_intel videobuf2_memops snd_hda_codec videobuf2_v4l2 dell_wmi dell_laptop videobuf2_core dell_smbios snd_hda_core videodev dcdbas rtsx_pci_ms irqbypass snd_hwdep media memstick snd_pcm hid_multitouch crct10dif_pclmul snd_seq_midi crc32_pclmul btusb btrtl ghash_clmulni_intel snd_seq_midi_event snd_rawmidi aesni_intel snd_seq snd_seq_device aes_x86_64 lrw snd_timer gf128mul glue_helper snd ablk_helper cryptd soundcore hci_uart btbcm btqca idma64 joydev input_leds shpchp btintel virt_dma mei_me serio_raw bluetooth mei processor_thermal_device
[ 44.871711] intel_lpss_pci intel_soc_dts_iosf acpi_als kfifo_buf industrialio intel_lpss_acpi intel_hid dell_smo8800 int3403_thermal int3400_thermal int3402_thermal intel_lpss acpi_pad sparse_keymap int340x_thermal_zone acpi_thermal_rel mac_hid parport_pc ppdev lp parport autofs4 usbhid rtsx_pci_sdmmc nouveau i915 mxm_wmi ttm i2c_algo_bit drm_kms_helper psmouse syscopyarea sysfillrect sysimgblt nvme fb_sys_fops uas nvme_core ahci drm usb_storage rtsx_pci libahci i2c_hid hid wmi pinctrl_sunrisepoint video pinctrl_intel fjes
[ 44.871727] CPU: 1 PID: 871 Comm: Xorg Not tainted 4.6.0-999-generic #201605082200
[ 44.871728] Hardware name: Dell Inc. XPS 15 9550/0N7TVV, BIOS 01.02.00 04/07/2016
[ 44.871729] 0000000000000286 0000000052e51aba ffff8808985bf918 ffffffff813f2ea3
[ 44.871731] ffff8808985bf968 0000000000000000 ffff8808985bf958 ffffffff8108294b
[ 44.871732] 00000e0200000000 ffff880891b41000 ffff8800219d9da4 ffff880891b42000
[ 44.871733] Call Trace:
[ 44.871736] [<ffffffff813f2ea3>] dump_stack+0x63/0x90
[ 44.871739] [<ffffffff8108294b>] __warn+0xcb/0xf0
[ 44.871740] [<ffffffff810829cf>] warn_slowpath_fmt+0x5f/0x80
[ 44.871749] [<ffffffffc022c6ac>] skl_update_other_pipe_wm+0x16c/0x180 [i915]
[ 44.871758] [<ffffffffc022c845>] skl_update_wm+0x185/0x640 [i915]
[ 44.871769] [<ffffffffc027a455>] ? gen9_write32+0x235/0x370 [i915]
[ 44.871782] [<ffffffffc02b88af>] ? intel_ddi_enable_transcoder_func+0x17f/0x260 [i915]
[ 44.871790] [<ffffffffc023060e>] intel_update_watermarks+0x1e/0x30 [i915]
[ 44.871802] [<ffffffffc029c821>] haswell_crtc_enable+0x321/0x8c0 [i915]
[ 44.871813] [<ffffffffc02991bb>] intel_atomic_commit+0x5fb/0xdd0 [i915]
[ 44.871825] [<ffffffffc00d9c31>] ? drm_atomic_check_only+0x181/0x600 [drm]
[ 44.871832] [<ffffffffc00da0e7>] drm_atomic_commit+0x37/0x60 [drm]
[ 44.871837] [<ffffffffc019b03a>] drm_atomic_helper_set_config+0x7a/0xb0 [drm_kms_helper]
[ 44.871844] [<ffffffffc00c9b42>] drm_mode_set_config_internal+0x62/0x100 [drm]
[ 44.871851] [<ffffffffc00cda90>] drm_mode_setcrtc+0x3e0/0x500 [drm]
[ 44.871856] [<ffffffffc00beab2>] drm_ioctl+0x152/0x540 [drm]
[ 44.871862] [<ffffffffc00cd6b0>] ? drm_mode_setplane+0x1b0/0x1b0 [drm]
[ 44.871864] [<ffffffff81237721>] do_vfs_ioctl+0xa1/0x5b0
[ 44.871866] [<ffffffff81090981>] ? __set_task_blocked+0x41/0xa0
[ 44.871867] [<ffffffff81093306>] ? __set_current_blocked+0x36/0x60
[ 44.871868] [<ffffffff81237ca9>] SyS_ioctl+0x79/0x90
[ 44.871869] [<ffffffff810935ce>] ? SyS_rt_sigprocmask+0x8e/0xc0
[ 44.871872] [<ffffffff81845476>] entry_SYSCALL_64_fastpath+0x1e/0xa8
[ 44.871873] ---[ end trace 12f151afa4c9e462 ]---
[ 53.708328] dell_wmi: Unknown WMI event type 0x12