Tested with 4.3.0-994-generic_4.3.0-994.201510062200

New warning during installation:
W: Possible missing firmware /lib/firmware/i915/skl_guc_ver4.bin for module i915

The original error remains:
[drm:intel_pipe_config_compare [i915]] *ERROR* mismatch in dpll_hw_state.wrpll

A new warning appears in the log:

Oct 07 09:31:25 pc-alvin kernel: ------------[ cut here ]------------
Oct 07 09:31:25 pc-alvin kernel: WARNING: CPU: 0 PID: 238 at /home/kernel/COD/linux/drivers/gpu/drm/i915/i915_gem_context.c:141 i915_gem_context_free+0x1df/0x1f0 [i915]()
Oct 07 09:31:25 pc-alvin kernel: WARN_ON_ONCE(!ppgtt)
Oct 07 09:31:25 pc-alvin kernel: Modules linked in:
Oct 07 09:31:25 pc-alvin kernel:  bnep nls_iso8859_1 xfs libcrc32c intel_rapl iosf_mbi x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_
Oct 07 09:31:25 pc-alvin kernel:  iptable_filter ip_tables parport_pc x_tables ppdev lp parport autofs4 drbg ansi_cprng algif_skcipher af_alg hid_generic hid_cherry usbhid hid dm_crypt uas usb_stor
Oct 07 09:31:25 pc-alvin kernel: CPU: 0 PID: 238 Comm: plymouthd Tainted: G        W       4.3.0-994-generic #201510062200
Oct 07 09:31:25 pc-alvin kernel: Hardware name: FUJITSU D3222-B1/D3222-B1, BIOS V4.6.5.4 R1.37.0 for D3222-B1x 08/06/2015
Oct 07 09:31:25 pc-alvin kernel:  ffffffffc02bf560 ffff880405fd3c38 ffffffff813a637d ffff880405fd3c80
Oct 07 09:31:25 pc-alvin kernel:  ffff880405fd3c70 ffffffff8107a586 0000000000000000 0000000000000000
Oct 07 09:31:25 pc-alvin kernel:  ffff880405cbc200 0000000000000000 ffff880405fd3d30 ffff880405fd3cd0
Oct 07 09:31:25 pc-alvin kernel: Call Trace:
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffff813a637d>] dump_stack+0x44/0x57
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffff8107a586>] warn_slowpath_common+0x86/0xc0
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffff8107a60c>] warn_slowpath_fmt+0x4c/0x50
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffffc02125df>] i915_gem_context_free+0x1df/0x1f0 [i915]
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffffc021260a>] context_idr_cleanup+0x1a/0x20 [i915]
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffff813a6b4b>] idr_for_each+0x9b/0xe0
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffffc02125f0>] ? i915_gem_context_free+0x1f0/0x1f0 [i915]
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffffc02135e3>] i915_gem_context_close+0x23/0x30 [i915]
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffffc02a1e5b>] i915_driver_preclose+0x2b/0x50 [i915]
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffffc0032b75>] drm_release+0xa5/0x500 [drm]
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffff811f38d4>] __fput+0xe4/0x210
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffff811f3a3e>] ____fput+0xe/0x10
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffff81096997>] task_work_run+0x77/0x90
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffff8107cf9d>] do_exit+0x2bd/0xaf0
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffff81065977>] ? __do_page_fault+0x1b7/0x430
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffff8107d84f>] do_group_exit+0x3f/0xa0
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffff8107d8c4>] SyS_exit_group+0x14/0x20
Oct 07 09:31:25 pc-alvin kernel:  [<ffffffff817b3c76>] entry_SYSCALL_64_fastpath+0x16/0x75
Oct 07 09:31:25 pc-alvin kernel: ---[ end trace 31fbc57b8abb5f10 ]---