Tested on SKLY03 with the testing kernel drm-intel-testing-2015-05-22.
this problem still exists.

output:
------------------
[ 1319.346675] ------------[ cut here ]------------
[ 1319.346707] WARNING: CPU: 0 PID: 5404 at drivers/gpu/drm/i915/intel_pm.c:3391 skl_update_other_pipe_wm+0x10b/0x148 [i915]()
[ 1319.346712] WARN_ON(!wm_changed)
[ 1319.346732] Modules linked in: dm_mod snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic ppdev snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep snd_pcm serio_raw pcspkr snd_timer snd i2c_i801 soundcore wmi battery parport_pc parport ac acpi_cpufreq i915 button video drm_kms_helper drm
[ 1319.346738] CPU: 0 PID: 5404 Comm: testdisplay Tainted: G     U  W       4.1.0-rc4_drm-intel-testing-2015-05-22+ #187
[ 1319.346740] Hardware name: Intel Corporation Skylake Client platform/Skylake Y LPDDR3 RVP3, BIOS SKLSE2R1.R00.B082.B00.1504240146 04/24/2015
[ 1319.346745]  0000000000000000 0000000000000009 ffffffff817a6ebc ffff880004b074e8
[ 1319.346749]  ffffffff8103ebde ffff8801634f9590 ffffffffa0085216 ffff880004b0760c
[ 1319.346752]  ffff880004b0760c ffff880163bb4000 ffff880163be9000 ffff8801634f958c
[ 1319.346753] Call Trace:
[ 1319.346764]  [<ffffffff817a6ebc>] ? dump_stack+0x40/0x50
[ 1319.346769]  [<ffffffff8103ebde>] ? warn_slowpath_common+0x98/0xb0
[ 1319.346792]  [<ffffffffa0085216>] ? skl_update_other_pipe_wm+0x10b/0x148 [i915]
[ 1319.346796]  [<ffffffff8103ec3b>] ? warn_slowpath_fmt+0x45/0x4a
[ 1319.346819]  [<ffffffffa0085216>] ? skl_update_other_pipe_wm+0x10b/0x148 [i915]
[ 1319.346842]  [<ffffffffa0085388>] ? skl_update_wm+0x135/0x5f9 [i915]
[ 1319.346846]  [<ffffffff8106a228>] ? down_trylock+0x20/0x29
[ 1319.346850]  [<ffffffff8107369c>] ? console_trylock+0x10/0x55
[ 1319.346854]  [<ffffffff81074e31>] ? vprintk_emit+0x30f/0x36f
[ 1319.346889]  [<ffffffffa00d8a5c>] ? haswell_crtc_enable+0x52c/0x94c [i915]
[ 1319.346922]  [<ffffffffa00d65f0>] ? __intel_set_mode+0x900/0x93a [i915]
[ 1319.346953]  [<ffffffffa00dbe46>] ? intel_crtc_set_config+0x3f2/0x53d [i915]
[ 1319.346967]  [<ffffffffa00184db>] ? drm_modeset_lock+0x4e/0xa3 [drm]
[ 1319.346988]  [<ffffffffa000c229>] ? drm_mode_set_config_internal+0x4e/0xd2 [drm]
[ 1319.346996]  [<ffffffffa005b13d>] ? restore_fbdev_mode+0xac/0xc3 [drm_kms_helper]
[ 1319.347011]  [<ffffffffa005c93e>] ? drm_fb_helper_restore_fbdev_mode_unlocked+0x1e/0x54 [drm_kms_helper]
[ 1319.347018]  [<ffffffffa005c9a2>] ? drm_fb_helper_set_par+0x2e/0x32 [drm_kms_helper]
[ 1319.347047]  [<ffffffffa00e86eb>] ? intel_fbdev_set_par+0x11/0x55 [i915]
[ 1319.347053]  [<ffffffff813450ad>] ? number.isra.13+0x11f/0x215
[ 1319.347060]  [<ffffffff813867f5>] ? fb_set_var+0x250/0x33b
[ 1319.347064]  [<ffffffff810e939c>] ? shmem_undo_range+0x455/0x46b
[ 1319.347069]  [<ffffffff81345d1a>] ? vsnprintf+0x83/0x3b9
[ 1319.347084]  [<ffffffff8137f3a1>] ? fbcon_blank+0x75/0x228
[ 1319.347089]  [<ffffffff810df8b0>] ? file_ra_state_init+0xc/0x1d
[ 1319.347095]  [<ffffffff813d6291>] ? do_unblank_screen+0xef/0x168
[ 1319.347100]  [<ffffffff813ce981>] ? vt_ioctl+0x4de/0xf59
[ 1319.347106]  [<ffffffff813c5f68>] ? tty_ioctl+0x954/0x9ba
[ 1319.347109]  [<ffffffff811217f3>] ? do_filp_open+0x2b/0x6f
[ 1319.347114]  [<ffffffff811234f6>] ? do_vfs_ioctl+0x360/0x424
[ 1319.347117]  [<ffffffff8112ae18>] ? __fd_install+0x15/0x40
[ 1319.347121]  [<ffffffff81123603>] ? SyS_ioctl+0x49/0x7a
[ 1319.347125]  [<ffffffff817aca17>] ? system_call_fastpath+0x12/0x6a
[ 1319.347129] ---[ end trace 76ca6edff58a8716 ]---
[ 1319.347134] ------------[ cut here ]------------