[Intel-gfx] [PATCH 08/13] drm/i915: Delay the relase of the forcewake by a jiffie

[Rodrigo Vivi]

From: Chris Wilson <chris at chris-wilson.co.uk>

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.

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.

Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi at gmail.com>
---
 drivers/gpu/drm/i915/i915_dma.c     |  6 ++++--
 drivers/gpu/drm/i915/i915_drv.h     |  3 +++
 drivers/gpu/drm/i915/intel_uncore.c | 30 ++++++++++++++++++++++++++++--
 3 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index 32e8368..a09a9c7 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1794,8 +1794,6 @@ int i915_driver_unload(struct drm_device *dev)
 	list_del(&dev_priv->gtt.base.global_link);
 	WARN_ON(!list_empty(&dev_priv->vm_list));
 	drm_mm_takedown(&dev_priv->gtt.base.mm);
-	if (dev_priv->regs != NULL)
-		pci_iounmap(dev->pdev, dev_priv->regs);
 
 	drm_vblank_cleanup(dev);
 
@@ -1807,6 +1805,10 @@ int i915_driver_unload(struct drm_device *dev)
 
 	dev_priv->gtt.base.cleanup(&dev_priv->gtt.base);
 
+	intel_uncore_fini(dev);
+	if (dev_priv->regs != NULL)
+		pci_iounmap(dev->pdev, dev_priv->regs);
+
 	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 8c52cbd..c171285 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -408,6 +408,8 @@ struct intel_uncore {
 
 	unsigned fifo_count;
 	unsigned forcewake_count;
+
+	struct delayed_work force_wake_work;
 };
 
 #define DEV_INFO_FOR_EACH_FLAG(func, sep) \
@@ -1791,6 +1793,7 @@ 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 8649f1c..462cc7f 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;
+
+	flush_delayed_work(&dev_priv->uncore.force_wake_work);
+}
+
 static void intel_uncore_forcewake_reset(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -306,8 +328,12 @@ 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);
 }
 
-- 
1.8.1.4