From 95736720fc866eadb2ce1789631b907c0f38cb7c Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Thu, 12 May 2011 22:17:09 +0100
Subject: [PATCH] drm/i915: Cache GT fifo count for SandyBridge
Git-commit: 95736720fc866eadb2ce1789631b907c0f38cb7c
Patch-mainline: 3.1-rc1

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@chris-wilson.co.uk>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Keith Packard <keithp@keithp.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/i915/i915_drv.c |   15 ++++++++++-----
 drivers/gpu/drm/i915/i915_drv.h |    1 +
 drivers/gpu/drm/i915/i915_reg.h |    1 +
 3 files changed, 12 insertions(+), 5 deletions(-)

--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -367,12 +367,17 @@ void gen6_gt_force_wake_put(struct drm_i
 
 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 < GT_FIFO_NUM_RESERVED_ENTRIES ) {
+		int loop = 500;
+		u32 fifo = I915_READ_NOTRACE(GT_FIFO_FREE_ENTRIES);
+		while (fifo <= GT_FIFO_NUM_RESERVED_ENTRIES && loop--) {
+			udelay(10);
+			fifo = I915_READ_NOTRACE(GT_FIFO_FREE_ENTRIES);
+		}
+		WARN_ON(loop < 0 && fifo <= GT_FIFO_NUM_RESERVED_ENTRIES);
+		dev_priv->gt_fifo_count = fifo;
 	}
+	dev_priv->gt_fifo_count--;
 }
 
 static int i915_drm_freeze(struct drm_device *dev)
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -283,6 +283,7 @@ typedef struct drm_i915_private {
 	int relative_constants_mode;
 
 	void __iomem *regs;
+	u32 gt_fifo_count;
 
 	struct intel_gmbus {
 		struct i2c_adapter adapter;
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -3385,6 +3385,7 @@
 #define    FORCEWAKE_MT_ENABLE			(1<<5)
 
 #define  GT_FIFO_FREE_ENTRIES			0x120008
+#define    GT_FIFO_NUM_RESERVED_ENTRIES		20
 
 #define GEN6_UCGCTL2				0x9404
 # define GEN6_RCZUNIT_CLOCK_GATE_DISABLE		(1 << 13)
