drm/i915: Terminate the FORCE WAKE after we have finished reading

Once we have read the value out of the GT power well, we need to remove
the FORCE WAKE bit to allow the system to auto-power down.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_drv.c

@@ -244,6 +244,28 @@ void intel_detect_pch (struct drm_device *dev)
 	}
 }
 
+void __gen6_force_wake_get(struct drm_i915_private *dev_priv)
+{
+	int count;
+
+	count = 0;
+	while (count++ < 50 && (I915_READ_NOTRACE(FORCEWAKE_ACK) & 1))
+		udelay(10);
+
+	I915_WRITE_NOTRACE(FORCEWAKE, 1);
+	POSTING_READ(FORCEWAKE);
+
+	count = 0;
+	while (count++ < 50 && (I915_READ_NOTRACE(FORCEWAKE_ACK) & 1) == 0)
+		udelay(10);
+}
+
+void __gen6_force_wake_put(struct drm_i915_private *dev_priv)
+{
+	I915_WRITE_NOTRACE(FORCEWAKE, 0);
+	POSTING_READ(FORCEWAKE);
+}
+
 static int i915_drm_freeze(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;

drivers/gpu/drm/i915/i915_drv.h

@@ -1341,17 +1341,20 @@ __i915_write(64, q)
  * must be set to prevent GT core from power down and stale values being
  * returned.
  */
+void __gen6_force_wake_get(struct drm_i915_private *dev_priv);
+void __gen6_force_wake_put (struct drm_i915_private *dev_priv);
 static inline u32 i915_safe_read(struct drm_i915_private *dev_priv, u32 reg)
 {
-	if (IS_GEN6(dev_priv->dev)) {
-		I915_WRITE_NOTRACE(FORCEWAKE, 1);
-		POSTING_READ(FORCEWAKE);
-		/* XXX How long do we really need to wait here?
-		 * Will different registers/engines require different periods?
-		 */
-		udelay(100);
-	}
-	return I915_READ(reg);
+	u32 val;
+
+	if (dev_priv->info->gen >= 6) {
+		__gen6_force_wake_get(dev_priv);
+		val = I915_READ(reg);
+		__gen6_force_wake_put(dev_priv);
+	} else
+		val = I915_READ(reg);
+
+	return val;
 }
 
 static inline void

drivers/gpu/drm/i915/i915_reg.h

@@ -3115,4 +3115,5 @@
 #define  EDP_LINK_TRAIN_VOL_EMP_MASK_SNB	(0x3f<<22)
 
 #define  FORCEWAKE				0xA18C
+#define  FORCEWAKE_ACK				0x130090
 #endif /* _I915_REG_H_ */