with mesa git after 2abe4f8d7dcdcff75c28958e1a691ebf6cdee1ac, radeon is failing
intermittently, with the following errors:

DRI_PRIME=1 glxgears 
radeon: Failed to allocate virtual address for buffer:
radeon:    size      : 65536 bytes
radeon:    alignment : 4096 bytes
radeon:    domains   : 4
radeon:    va        : 0x0000000000800000
radeon: Failed to deallocate virtual address for buffer:
radeon:    size      : 65536 bytes
radeon:    va        : 0x0000000000800000
radeon: Failed to allocate virtual address for buffer:
radeon:    size      : 65536 bytes
radeon:    alignment : 4096 bytes
radeon:    domains   : 4
radeon:    va        : 0x0000000000800000
radeon: Failed to deallocate virtual address for buffer:
radeon:    size      : 65536 bytes
radeon:    va        : 0x0000000000800000
radeonsi: Failed to create a context.
radeon: Failed to allocate virtual address for buffer:
radeon:    size      : 65536 bytes
radeon:    alignment : 4096 bytes
radeon:    domains   : 4
radeon:    va        : 0x0000000000800000
radeon: Failed to deallocate virtual address for buffer:
radeon:    size      : 65536 bytes
radeon:    va        : 0x0000000000800000
radeon: Failed to allocate virtual address for buffer:
radeon:    size      : 65536 bytes
radeon:    alignment : 4096 bytes
radeon:    domains   : 4
radeon:    va        : 0x0000000000800000
radeon: Failed to deallocate virtual address for buffer:
radeon:    size      : 65536 bytes
radeon:    va        : 0x0000000000800000
radeonsi: Failed to create a context.
X Error of failed request:  BadValue (integer parameter out of range for
operation)
  Major opcode of failed request:  154 (GLX)
  Minor opcode of failed request:  3 (X_GLXCreateContext)
  Value in failed request:  0x0
  Serial number of failed request:  30
  Current serial number in output stream:  32

dmesg:
[  999.461532] [drm] probing gen 2 caps for device 8086:9c18 = 5323c42/0
[  999.461537] [drm] PCIE gen 2 link speeds already enabled
[  999.468703] [drm] PCIE GART of 2048M enabled (table at 0x00000000002E8000).
[  999.468827] radeon 0000:03:00.0: WB enabled
[  999.468829] radeon 0000:03:00.0: fence driver on ring 0 use gpu addr
0x0000000080000c00 and cpu addr 0xffff8801a322bc00
[  999.468831] radeon 0000:03:00.0: fence driver on ring 1 use gpu addr
0x0000000080000c04 and cpu addr 0xffff8801a322bc04
[  999.468832] radeon 0000:03:00.0: fence driver on ring 2 use gpu addr
0x0000000080000c08 and cpu addr 0xffff8801a322bc08
[  999.468834] radeon 0000:03:00.0: fence driver on ring 3 use gpu addr
0x0000000080000c0c and cpu addr 0xffff8801a322bc0c
[  999.468835] radeon 0000:03:00.0: fence driver on ring 4 use gpu addr
0x0000000080000c10 and cpu addr 0xffff8801a322bc10
[  999.470457] radeon 0000:03:00.0: fence driver on ring 5 use gpu addr
0x0000000000075a18 and cpu addr 0xffffc90001435a18
[  999.480817] radeon 0000:03:00.0: VCE init error (-22).
[ 1000.212739] [drm:r600_ring_test [radeon]] *ERROR* radeon: ring 0 test failed
(scratch(0x850C)=0xCAFEDEAD)
[ 1000.212764] [drm:si_resume [radeon]] *ERROR* si startup failed on resume