[PATCH 5/5] drm/i915: Estimate and update missed vblanks.

[Dhinakaran Pandiyan]

The frame counter may have got reset between disabling and enabling vblank
interrupts due to DMC putting the hardware to DC5/6 state if PSR was
active. The frame counter also could have stalled if PSR is active in cases
where there is no DMC. The frame counter resetting as a user visible impact
of screen freezes. Use drm_vblank_restore() to compute missed vblanks
in the duration for which vblank interrupts are disabled. There's no need
particularly check if PSR was active in the interrupt disabled duration.

Enabling vblank interrupts wakes up the hardware from DC5/6 and prevents it
from going back again as long as the there are pending interrupts. So, we
don't have to explicity disallow DC5/6 after enabling vblank interrupts
to keep the counter running.

Let's not apply this to CHV for now, as enabling interrupts does not
prevent the hardware from activating PSR and thereby stalling the counter.

Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
---
 drivers/gpu/drm/i915/i915_irq.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 3517c6548e2c..db3466ec6faa 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2956,6 +2956,9 @@ static int ironlake_enable_vblank(struct drm_device *dev, unsigned int pipe)
 	ilk_enable_display_irq(dev_priv, bit);
 	spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
 
+	if (HAS_PSR(dev_priv))
+		drm_vblank_restore(dev, pipe);
+
 	return 0;
 }
 
@@ -2968,6 +2971,9 @@ static int gen8_enable_vblank(struct drm_device *dev, unsigned int pipe)
 	bdw_enable_pipe_irq(dev_priv, pipe, GEN8_PIPE_VBLANK);
 	spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
 
+	if (HAS_PSR(dev_priv))
+		drm_vblank_restore(dev, pipe);
+
 	return 0;
 }
 
-- 
2.11.0