drm/i915: clear the FPGA_DBG_RM_NOCLAIM bit at driver init

Otherwise, if the BIOS did anything wrong, our first I915_{WRITE,READ}
will give us "unclaimed register"  messages.

V2: Even earlier.
V3: Move it to intel_early_sanitize_regs.

Bugzilla: http://bugs.freedesktop.org/show_bug.cgi?id=58897
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_dma.c

@@ -1452,6 +1452,22 @@ static void i915_dump_device_info(struct drm_i915_private *dev_priv)
 #undef DEV_INFO_SEP
 }
 
+/**
+ * intel_early_sanitize_regs - clean up BIOS state
+ * @dev: DRM device
+ *
+ * This function must be called before we do any I915_READ or I915_WRITE. Its
+ * purpose is to clean up any state left by the BIOS that may affect us when
+ * reading and/or writing registers.
+ */
+static void intel_early_sanitize_regs(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	if (IS_HASWELL(dev))
+		I915_WRITE_NOTRACE(FPGA_DBG, FPGA_DBG_RM_NOCLAIM);
+}
+
 /**
  * i915_driver_load - setup chip and create an initial config
  * @dev: DRM device
@@ -1542,6 +1558,8 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 		goto put_gmch;
 	}
 
+	intel_early_sanitize_regs(dev);
+
 	aperture_size = dev_priv->gtt.mappable_end;
 
 	dev_priv->gtt.mappable =