Hi Mario, On Saturday 13 October 2012 02:28:03 Mario Kleiner wrote: > On 11.10.12 16:19, Laurent Pinchart wrote: > > On Monday 08 October 2012 14:50:39 Rob Clark wrote: > >> From: Rob Clark <rob@xxxxxx> > > ... > > > Do you know why some drivers don't call drm_vblank_count_and_time() ? For > > instance nouveau sets the sequence to 0 and uses do_gettimeofday(), but it > > looks like it could just call drm_vblank_count_and_time(). > > At least nouveau could use it. Lucas Stach and me wrote patches for > nouveau-kms, and they went through many iterations and missed many > kernel merge windows due to slow review until i think both of us got > tired of resubmitting with tiny changes. I totally understand the feeling, but please don't give up. You can CC me on the next iteration, I'll make sure to review the patches (even though I have no experience with the nouveau driver). > The latest iteration is posted by Lucas on nouveau-devel from 26. April > 2012. Not sure if they'd still apply after the nouveau-kms rewrite. I'll > probably give them another try once that has landed when i have some spare > time. > > In principle it's very simple to use drm_vblank_count_and_time(). A > driver needs to > > 1. Call drm_handle_vblank() from its vblank irq handler. > > 2. Make sure that in the vblank of pageflip completion > drm_handle_vblank() is called before drm_vblank_count_and_time(), so the > latter picks up updated counts and timestamps. > > 3. Big bonus for high precision and robustness: Implement the > driver->get_vblank_timestamp() hook to provide a precise vblank > timestamp. One simple way to do that is like radeon-kms or intel-kms do > it: Call back into drm_calc_vbltimestamp_from_scanoutpos() and provide > the driver->get_scanout_position() function - a function that returns > the current hardware scanline counter. This is precise down to ~ 10 > microseconds (at least confirmed by measurements on > intel,radeon,nouveau) and robust against delayed vblank irq handling. > > -mario -- Regards, Laurent Pinchart _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
