right, i think it's a known issue, as the iommu failed to get clks:
[ÂÂÂ 1.525153] rk_iommu ff8f3f00.iommu: Failed to get clk 'iface': -2
[ÂÂÂ 1.525316] rk_iommu: probe of ff8f3f00.iommu failed with error -2
[ÂÂÂ 1.525484] rk_iommu ff903f00.iommu: Failed to get clk 'iface': -2
[ÂÂÂ 1.525643] rk_iommu: probe of ff903f00.iommu failed with error -2
there's a followed patch to add those clks to the dtsi, and also a fix patch to make those clks optional(by heiko):
https://www.spinics.net/lists/arm-kernel/msg645696.html
http://lists.infradead.org/pipermail/linux-rockchip/2018-April/020349.html
[ 15.586502] [drm:drm_atomic_helper_wait_for_dependencies] *ERROR* [CRTC:30:crtc-0] flip_done timed out
[ 25.826490] [drm:drm_atomic_helper_wait_for_dependencies] *ERROR* [CONNECTOR:37:HDMI-A-1] flip_done timed out
[ 36.066490] [drm:drm_atomic_helper_wait_for_dependencies] *ERROR* [PLANE:28:plane-0] flip_done timed out
[ 36.066504] [drm:drm_calc_timestamping_constants] crtc 30: hwmode: htotal 2200, vtotal 1125, vdisplay 1080
[ 36.066508] [drm:drm_calc_timestamping_constants] crtc 30: clock 148500 kHz framedur 16666666 linedur 14814
[ 36.076535] rockchip-vop ff8f0000.vop: [drm:vop_crtc_atomic_flush] *ERROR* VOP vblank IRQ stuck for 10 ms
[ 36.076577] WARNING: CPU: 1 PID: 83 at drivers/gpu/drm/rockchip/rockchip_drm_vop.c:1004 vop_crtc_atomic_flush+0x1c0/0x1c8