Comment # 17 on bug 80029 from Mike Lothian

After remembering to copy hdmi-extra.conf to default.conf in
/usr/share/pulseaudio/alsa-mixer/profile-sets/ (I think that's a known bug) my
5.1 surround worked just fine

I noticed this in the logs after playing Big Buck Bunny
(big_buck_bunny_1080p_surround.avi)

[  1043.140] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 62525 < target_msc 62526
[  1153.407] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 69140 < target_msc 69141
[  1162.907] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 69709 < target_msc 69710
[  1237.257] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 74170 < target_msc 74171
[  1241.357] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 74415 < target_msc 74416
[  1241.407] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 74418 < target_msc 74419
[  1241.941] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 74450 < target_msc 74451
[  1253.324] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 75131 < target_msc 75132
[  1261.408] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 75615 < target_msc 75616
[  1261.595] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 75625 < target_msc 75626
[  1266.474] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 75918 < target_msc 75919
[  1286.541] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 77121 < target_msc 77122
[  1287.691] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 77190 < target_msc 77191
[  1288.441] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 77235 < target_msc 77236
[  1292.691] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 77490 < target_msc 77491
[  2152.825] (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip
completion event has impossible msc 129098 < target_msc 129099

I'm guessing this is unrelated though