drm/i915: Delay the release of the forcewake by a jiffie

Obtaining the forcwake requires expensive and time consuming
serialisation. And we often try to obtain the forcewake multiple times
in very quick succession. We can reduce the overhead of these sequences
by delaying the forcewake release, and so not hammer the hw quite so
hard.

I was hoping this would help with the spurious
[drm:__gen6_gt_force_wake_mt_get] *ERROR* Timed out waiting for forcewake old ack to clear.
found on Haswell. Alas not.

v2: Fix teardown ordering - unmap the regs after turning off forcewake,
and make sure we do turn off forcewake - both found by Ville.

v3: As we introduce intel_uncore_fini(), use it to make sure everything
is disabled before we hand back to the BIOS.

Note: I have no claims for improved performance, stablity or power
comsumption for this patch. We should not be hitting the registers often
enough for this to improve benchmarks, but given the nature of our hw it
is likely to improve long term stability.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 31 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index 8649f1c36b0..f2753d9fb09 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -204,6 +204,18 @@ static void vlv_force_wake_put(struct drm_i915_private *dev_priv)
 	gen6_gt_check_fifodbg(dev_priv);
 }
 
+static void gen6_force_wake_work(struct work_struct *work)
+{
+	struct drm_i915_private *dev_priv =
+		container_of(work, typeof(*dev_priv), uncore.force_wake_work.work);
+	unsigned long irqflags;
+
+	spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
+	if (--dev_priv->uncore.forcewake_count == 0)
+		dev_priv->uncore.funcs.force_wake_put(dev_priv);
+	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
+}
+
 void intel_uncore_early_sanitize(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -216,6 +228,9 @@ void intel_uncore_init(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
+	INIT_DELAYED_WORK(&dev_priv->uncore.force_wake_work,
+			  gen6_force_wake_work);
+
 	if (IS_VALLEYVIEW(dev)) {
 		dev_priv->uncore.funcs.force_wake_get = vlv_force_wake_get;
 		dev_priv->uncore.funcs.force_wake_put = vlv_force_wake_put;
@@ -261,6 +276,16 @@ void intel_uncore_init(struct drm_device *dev)
 	}
 }
 
+void intel_uncore_fini(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	flush_delayed_work(&dev_priv->uncore.force_wake_work);
+
+	/* Paranoia: make sure we have disabled everything before we exit. */
+	intel_uncore_sanitize(dev);
+}
+
 static void intel_uncore_forcewake_reset(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -306,8 +331,12 @@ void gen6_gt_force_wake_put(struct drm_i915_private *dev_priv)
 	unsigned long irqflags;
 
 	spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
-	if (--dev_priv->uncore.forcewake_count == 0)
-		dev_priv->uncore.funcs.force_wake_put(dev_priv);
+	if (--dev_priv->uncore.forcewake_count == 0) {
+		dev_priv->uncore.forcewake_count++;
+		mod_delayed_work(dev_priv->wq,
+				 &dev_priv->uncore.force_wake_work,
+				 1);
+	}
 	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
 }