[PATCH 5/8] drm/i915: simplify FBC start/stop at invalidate/flush

[Paulo Zanoni <przanoni@gmail.com>]

From: Paulo Zanoni <paulo.r.zanoni@intel.com>

The problem with calling intel_fbc_update() at flush is that it fully
rechecks and recomputes the FBC state, and that includes reallocating
the CFB, which requires a struct_mutex lock that we don't always have.

The lack of struct_mutex lock can be considered a regression from:

commit dbef0f15b5c83231dacb214dbf9a6dba063ca21c
Author: Paulo Zanoni <paulo.r.zanoni@intel.com>
Date:   Fri Feb 13 17:23:46 2015 -0200
    drm/i915: add frontbuffer tracking to FBC

So introduce intel_fbc_stop() that doesn't unset fbc.crtc, then call
stop/enable at invalidate/flush.

Notice that invalidate/flush is only called by the frontbuffer
tracking infrastrucutre, so it's safe to not do a full
intel_fbc_update() here.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
---
 drivers/gpu/drm/i915/intel_fbc.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
index 316feb1..0a66814 100644
--- a/drivers/gpu/drm/i915/intel_fbc.c
+++ b/drivers/gpu/drm/i915/intel_fbc.c
@@ -422,7 +422,7 @@ static void intel_fbc_enable(struct drm_crtc *crtc)
 	schedule_delayed_work(&work->work, msecs_to_jiffies(50));
 }
 
-static void __intel_fbc_disable(struct drm_device *dev)
+static void intel_fbc_stop(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
@@ -434,6 +434,13 @@ static void __intel_fbc_disable(struct drm_device *dev)
 		return;
 
 	dev_priv->display.disable_fbc(dev);
+}
+
+static void __intel_fbc_disable(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	intel_fbc_stop(dev);
 	dev_priv->fbc.crtc = NULL;
 }
 
@@ -753,7 +760,7 @@ void intel_fbc_invalidate(struct drm_i915_private *dev_priv,
 	dev_priv->fbc.busy_bits |= (fbc_bits & frontbuffer_bits);
 
 	if (dev_priv->fbc.busy_bits)
-		__intel_fbc_disable(dev);
+		intel_fbc_stop(dev);
 
 	mutex_unlock(&dev_priv->fbc.lock);
 }
@@ -770,8 +777,11 @@ void intel_fbc_flush(struct drm_i915_private *dev_priv,
 
 	dev_priv->fbc.busy_bits &= ~frontbuffer_bits;
 
-	if (!dev_priv->fbc.busy_bits)
-		__intel_fbc_update(dev);
+	if (!dev_priv->fbc.busy_bits && dev_priv->fbc.crtc) {
+		if (dev_priv->fbc.enabled)
+			intel_fbc_stop(dev);
+		intel_fbc_enable(&dev_priv->fbc.crtc->base);
+	}
 
 out:
 	mutex_unlock(&dev_priv->fbc.lock);
-- 
2.1.4

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