[PATCH 09/12] drm/i915: wait for a vblank instead of 50ms when enabling FBC

[Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx>]

Instead of waiting for 50ms, just wait until the next vblank, since
it's the minimum requirement.

This moves PC7 residency on my specific BDW machine running Cinnamon
from 60-70% to 84-89%. Without FBC, I get 20-25%. I'm using a
3200x1800 eDP panel. Notice: this was the case when the patch was
originally proposed, the order of the FBC patches changed since then,
so the actual numbers might be slightly different now.

v2:
  - Rebase after changing the patch order.
  - Update the commit message.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx>
---
 drivers/gpu/drm/i915/i915_drv.h  |  2 +-
 drivers/gpu/drm/i915/intel_fbc.c | 12 +++---------
 2 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 9418bd5..ea08714 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -919,9 +919,9 @@ struct i915_fbc {
 
 	struct intel_fbc_work {
 		bool scheduled;
+		u32 scheduled_vblank;
 		struct work_struct work;
 		struct drm_framebuffer *fb;
-		unsigned long enable_jiffies;
 	} work;
 
 	const char *no_fbc_reason;
diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
index aa82075..72de8a1 100644
--- a/drivers/gpu/drm/i915/intel_fbc.c
+++ b/drivers/gpu/drm/i915/intel_fbc.c
@@ -391,7 +391,6 @@ static void intel_fbc_work_fn(struct work_struct *__work)
 		container_of(__work, struct drm_i915_private, fbc.work.work);
 	struct intel_fbc_work *work = &dev_priv->fbc.work;
 	struct intel_crtc *crtc = dev_priv->fbc.crtc;
-	unsigned long delay_jiffies = msecs_to_jiffies(50);
 
 retry:
 	/* Delay the actual enabling to let pageflipping cease and the
@@ -400,14 +399,9 @@ retry:
 	 * vblank to pass after disabling the FBC before we attempt
 	 * to modify the control registers.
 	 *
-	 * A more complicated solution would involve tracking vblanks
-	 * following the termination of the page-flipping sequence
-	 * and indeed performing the enable as a co-routine and not
-	 * waiting synchronously upon the vblank.
-	 *
 	 * WaFbcWaitForVBlankBeforeEnable:ilk,snb
 	 */
-	wait_remaining_ms_from_jiffies(work->enable_jiffies, delay_jiffies);
+	intel_wait_for_vblank(dev_priv->dev, crtc->pipe);
 
 	mutex_lock(&dev_priv->fbc.lock);
 
@@ -416,7 +410,7 @@ retry:
 		goto out;
 
 	/* Were we delayed again while this function was sleeping? */
-	if (time_after(work->enable_jiffies + delay_jiffies, jiffies)) {
+	if (drm_crtc_vblank_get(&crtc->base) == work->scheduled_vblank) {
 		mutex_unlock(&dev_priv->fbc.lock);
 		goto retry;
 	}
@@ -449,7 +443,7 @@ static void intel_fbc_schedule_activation(struct intel_crtc *crtc)
 	 * jiffy count. */
 	work->fb = crtc->base.primary->fb;
 	work->scheduled = true;
-	work->enable_jiffies = jiffies;
+	work->scheduled_vblank = drm_crtc_vblank_count(&crtc->base);
 
 	schedule_work(&work->work);
 }
-- 
2.6.2

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