On Wed, Mar 30, 2016 at 03:41:26PM +0200, Maarten Lankhorst wrote:
Op 30-03-16 om 15:13 schreef Ville Syrjälä:
On Tue, Mar 29, 2016 at 03:38:55PM +0200, Maarten Lankhorst wrote:
This function is useful for gen2 intel devices which have no frame counter, but need a way to determine the current vblank count without racing with the vblank interrupt handler.
intel_pipe_update_start checks if no vblank interrupt will occur during vblank evasion, but cannot check whether the vblank handler has run to completion. This function uses the timestamps to determine when the last vblank has happened, and interpolates from there.
Didn't really read it in detail, but on a glance it seems too complicated to me. All we should really need is something like this:
drm_vblank_get(); drm_update_vblank_count(); accurate = drm_vblank_count();
Updating from non vblank irq context might cause the vblank clock to drift, or at least contend the vblank lock.
I don't see a problem. The scanout position is anyway used to fix up the timestamp.
This is why I call drm_vblank_count_and_time, and then interpolate as if update_vblank_count was called on the result.
~Maarten