[Intel-gfx] [PATCH] drm/i915: Keep vblanks enabled during the entire pipe update

[ville.syrjala at linux.intel.com]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

We currently hold a vblank referenced while trying to evade the
vblank, but we drop it as soon as we've done that. After all the
planes have been committed we are quite likely to grab a new vblank
reference for delivering the flip event. This causes the vblank
interrupt to do a enable->enable->disable ping-pong during many
commits. If we instead hang on to the original vblank reference
across the entire commit we can eliminate that ping-pong.

Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_sprite.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
index b931d0bd7a64..bf353e9130b8 100644
--- a/drivers/gpu/drm/i915/intel_sprite.c
+++ b/drivers/gpu/drm/i915/intel_sprite.c
@@ -137,8 +137,6 @@ void intel_pipe_update_start(struct intel_crtc *crtc)
 
 	finish_wait(wq, &wait);
 
-	drm_crtc_vblank_put(&crtc->base);
-
 	crtc->debug.scanline_start = scanline;
 	crtc->debug.start_vbl_time = ktime_get();
 	crtc->debug.start_vbl_count = intel_crtc_get_vblank_counter(crtc);
@@ -185,6 +183,15 @@ void intel_pipe_update_end(struct intel_crtc *crtc, struct intel_flip_work *work
 		crtc->base.state->event = NULL;
 	}
 
+	/*
+	 * The reference was taken in intel_pipe_update_start(). It could
+	 * have been dropped as soon as the vblank was evaded, but we hold
+	 * on to it until this time to avoid the extra vblank interrupt
+	 * enable->disable->enable ping-pong whenever we have to deliver
+	 * an event.
+	 */
+	drm_crtc_vblank_put(&crtc->base);
+
 	local_irq_enable();
 
 	if (intel_vgpu_active(dev_priv))
-- 
2.10.2