[drm:drm_wait_vblank [drm]] *ERROR* Unsupported type value 0xA, supported mask 0xB

[rusvdw]

I have this issue on a Dell XPS 13 9350 with the Dell D3100 dock running Ubuntu 16.04 (4.4.0-24-generic). Error in the syslog is slightly different:

[drm:drm_wait_vblank [drm]] *ERROR* Unsupported type value 0x75, supported mask 0x7400003f
[drm:drm_wait_vblank [drm]] *ERROR* Unsupported type value 0x4000074, supported mask 0x7400003f

This message is generated hundreds of times times per second and massively impacts performance when the displays are connected. This only happens when the primary display is set to one of the external displays. Keeping the laptop display as primary is a workable if annoying workaround.

GPU info:

lspci -vnn | grep VGA -A 12
00:02.0 VGA compatible controller [0300]: Intel Corporation Sky Lake Integrated Graphics [8086:1926] (rev 0a) (prog-if 00 [VGA controller])
DeviceName: Onboard IGD
Subsystem: Dell Skylake Integrated Graphics [1028:0704]
Flags: bus master, fast devsel, latency 0, IRQ 277
Memory at db000000 (64-bit, non-prefetchable) [size=16M]
Memory at 90000000 (64-bit, prefetchable) [size=256M]
I/O ports at f000 [size=64]
Expansion ROM at <unassigned> [disabled]
Capabilities: <access denied>
Kernel driver in use: i915_bpo
Kernel modules: i915_bpo