When userland detected that this ioctl was supported (by version number check), it used it in a racy way -- dispatch delayed swap, wait for vblank, continue rendering. As there was no mechanism for it to wait for the swap to finish, sometimes it would render before the swap and garbage would be displayed on the screen. By removing the ioctl and returning -EINVAL, userland returns to its previous, correct rendering path of waiting for a vblank then dispatching a swap. The only path that could have used this ioctl correctly was page flipping, which relied on only one client running and emitting wait-for-vblank-before-rendering in the command stream. That path also falls back correctly, at the performance cost of not being able to queue up rendering before the flip occurs. Signed-off-by: Eric Anholt <eric@anholt.net> Signed-off-by: Dave Airlie <airlied@linux.ie>