[PATCH 3/4] drm/amd/display: Enter VRR BTR earlier.

[Mario Kleiner]

Use a 2 msecs switching headroom not only for slightly
delayed exiting of BTR mode, but now also for entering
it a bit before the max frame duration is exceeded.

With slowly changing time delay between successive flips
or with a bit of jitter in arrival of flips, this adapts
vblank early and prevents missed vblanks at the border
between non-BTR and BTR.

Testing on DCE-8, DCE-11 and DCN-1.0 shows that this more
often avoids skipped frames when moving across the BTR
boundary, especially on DCE-8 and DCE-11 with the followup
commit for dealing with pre-DCE-12 hw.

Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
---
 drivers/gpu/drm/amd/display/modules/freesync/freesync.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
index e56543c36eba..a965ab5466dc 100644
--- a/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
+++ b/drivers/gpu/drm/amd/display/modules/freesync/freesync.c
@@ -350,7 +350,7 @@ static void apply_below_the_range(struct core_freesync *core_freesync,
 			in_out_vrr->btr.frame_counter = 0;
 			in_out_vrr->btr.btr_active = false;
 		}
-	} else if (last_render_time_in_us > max_render_time_in_us) {
+	} else if (last_render_time_in_us + BTR_EXIT_MARGIN > max_render_time_in_us) {
 		/* Enter Below the Range */
 		in_out_vrr->btr.btr_active = true;
 	}
-- 
2.20.1