On 17/09/16 09:25 PM, Mario Kleiner wrote: > Pre DCE4 hw doesn't have reliable pageflip completion > interrupts, so instead polling for flip completion is > used from within the vblank irq handler to complete > page flips. > > This causes a race if pageflip ioctl is called close to > vblank: > > 1. pageflip ioctl queues execution of radeon_flip_work_func. > > 2. vblank irq fires, radeon_crtc_handle_vblank checks for > flip_status == FLIP_SUBMITTED finds none, no-ops. > > 3. radeon_flip_work_func runs inside vblank, decides to > set flip_status == FLIP_SUBMITTED and programs the > flip into hw. > > 4. hw executes flip immediately (because in vblank), but > as 2 already happened, the flip completion routine only > emits the flip completion event one refresh later -> > wrong vblank count/timestamp for completion and no > performance gain, as instead of delaying the flip until > next vblank, we now delay the next flip by 1 refresh > while waiting for the delayed flip completion event. > > Given we often don't gain anything due to this race, but > lose precision, prevent the programmed flip from executing > in vblank on pre DCE4 asics to avoid this race. > > On pre-AVIVO hw we can't program the hw for edge-triggered > flips, they always execute anywhere in vblank. Therefore delay > the actual flip programming until after vblank on pre-AVIVO. > > Signed-off-by: Mario Kleiner <mario.kleiner.de@xxxxxxxxx> Reviewed-by: Michel Dänzer <michel.daenzer@xxxxxxx> P.S. Please send radeon (and amdgpu) driver patches to the amd-gfx mailing list (as well). -- Earthling Michel Dänzer | http://www.amd.com Libre software enthusiast | Mesa and X developer _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
