[Intel-gfx] [PATCH] drm/i915: Delay the relase of the forcewake by a jiffie

[Chris Wilson]

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.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_dma.c     |  2 ++
 drivers/gpu/drm/i915/i915_drv.h     |  3 +++
 drivers/gpu/drm/i915/intel_uncore.c | 33 +++++++++++++++++++++++++++++++--
 3 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index 883990f..c0fb23e 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1800,6 +1800,8 @@ int i915_driver_unload(struct drm_device *dev)
 
 	dev_priv->gtt.base.cleanup(&dev_priv->gtt.base);
 
+	intel_uncore_fini(dev);
+
 	if (dev_priv->slab)
 		kmem_cache_destroy(dev_priv->slab);
 
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index a6354c3..8c93d93 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -406,6 +406,8 @@ struct intel_uncore {
 
 	unsigned fifo_count;
 	unsigned forcewake_count;
+
+	struct delayed_work force_wake_work;
 };
 
 #define DEV_INFO_FOR_EACH_FLAG(func, sep) \
@@ -1792,6 +1794,7 @@ extern void intel_uncore_early_sanitize(struct drm_device *dev);
 extern void intel_uncore_init(struct drm_device *dev);
 extern void intel_uncore_clear_errors(struct drm_device *dev);
 extern void intel_uncore_check_errors(struct drm_device *dev);
+extern void intel_uncore_fini(struct drm_device *dev);
 
 void
 i915_enable_pipestat(drm_i915_private_t *dev_priv, int pipe, u32 mask);
diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index 8f5bc86..50fdad7 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 +276,13 @@ 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;
+
+	cancel_delayed_work_sync(&dev_priv->uncore.force_wake_work);
+}
+
 void intel_uncore_sanitize(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -301,8 +323,15 @@ 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) {
+		if (dev_priv->uncore.force_wake_work.work.func) {
+			dev_priv->uncore.forcewake_count++;
+			mod_delayed_work(dev_priv->wq,
+					 &dev_priv->uncore.force_wake_work,
+					 1);
+		} else
+			dev_priv->uncore.funcs.force_wake_put(dev_priv);
+	}
 	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
 }
 
-- 
1.8.4.rc3