[Intel-gfx] [PATCH 23/30] drm/i915: Cache GT fifo count for SandyBridge

[Chris Wilson]

The read back of the available FIFO entries is vital for system
stability, but extremely costly. However, we only need a guide so as to
avoid eating into the reserved entries and since we are the only
consumer we can cache the read of the count from the last write.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.c |   14 +++++++++-----
 drivers/gpu/drm/i915/i915_drv.h |    1 +
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index c416c1d..1146abd 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -287,12 +287,16 @@ void __gen6_gt_force_wake_put(struct drm_i915_private *dev_priv)
 
 void __gen6_gt_wait_for_fifo(struct drm_i915_private *dev_priv)
 {
-	int loop = 500;
-	u32 fifo = I915_READ_NOTRACE(GT_FIFO_FREE_ENTRIES);
-	while (fifo < 20 && loop--) {
-		udelay(10);
-		fifo = I915_READ_NOTRACE(GT_FIFO_FREE_ENTRIES);
+	if (dev_priv->gt_fifo_count < 20 ) {
+		int loop = 500;
+		u32 fifo = I915_READ_NOTRACE(GT_FIFO_FREE_ENTRIES);
+		while (fifo < 20 && loop--) {
+			udelay(10);
+			fifo = I915_READ_NOTRACE(GT_FIFO_FREE_ENTRIES);
+		}
+		dev_priv->gt_fifo_count = fifo;
 	}
+	dev_priv->gt_fifo_count--;
 }
 
 static int i915_drm_freeze(struct drm_device *dev)
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 2f45228..c837e10 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -268,6 +268,7 @@ typedef struct drm_i915_private {
 	int relative_constants_mode;
 
 	void __iomem *regs;
+	u32 gt_fifo_count;
 
 	struct intel_gmbus {
 		struct i2c_adapter adapter;
-- 
1.7.4.1