R9285 Tonga it seems that on various agd5f DC kernels using

mpv -fs --hwdec=vdpau <a 2160p60 very high bitrate video>

screen is 1920x1080 DVI-D

will sometimes produces logging with a few

[drm:fill_plane_attributes [amdgpu]] *ERROR* Unable to reserve buffer

grepping kernel log shows this is not new + only seems to happen with a DC
kernel (I spend more time in non DC kernels and have no instances with those).

First record April 3rd, but then it doesn't always happen and I don't always
run that test so it could have started earlier. 

With just a few of the errors no bad effects noticed.

Today, with current agd5f amd-staging-4.11 I got a display lock with logging
below, I can't reproduce the lock, but can get a few of the messages to show.

Jun  6 17:48:16 ph4 kernel: [drm:fill_plane_attributes [amdgpu]] *ERROR* Unable
to reserve buffer
Jun  6 17:48:47 ph4 last message repeated 6136 times
Jun  6 17:49:33 ph4 last message repeated 9208 times
Jun  6 17:49:33 ph4 kernel: sysrq: SysRq : Emergency Sync
Jun  6 17:49:33 ph4 kernel: Emergency Sync complete
Jun  6 17:49:33 ph4 kernel: [drm:fill_plane_attributes [amdgpu]] *ERROR* Unable
to reserve buffer
Jun  6 17:49:34 ph4 last message repeated 306 times
Jun  6 17:49:34 ph4 kernel: sysrq: SysRq : Emergency Remount R/O
Jun  6 17:49:34 ph4 kernel: [drm:fill_plane_attributes [amdgpu]] *ERROR* Unable
to reserve buffer