diff --git a/drivers/gpu/drm/i915/intel_overlay.c b/drivers/gpu/drm/i915/intel_overlay.c
index f1bf0b0..59d616d 100644
--- a/drivers/gpu/drm/i915/intel_overlay.c
+++ b/drivers/gpu/drm/i915/intel_overlay.c
@@ -174,11 +174,17 @@ struct overlay_registers {
 #define OVERLAY_NONPHYSICAL(dev) (IS_G33(dev) || IS_I965G(dev))
 #define OVERLAY_EXISTS(dev) (!IS_G4X(dev) && !IS_IGDNG(dev))
 
+static int overlay_map_counter;
+#define OVERLAY_REGFILE_SIZE 0x100
+#define OVERLAY_REGFILE_START 0x30100
 
 static struct overlay_registers *intel_overlay_map_regs_atomic(struct intel_overlay *overlay)
 {
         drm_i915_private_t *dev_priv = overlay->dev->dev_private;
 	struct overlay_registers *regs;
+	unsigned int i, bad = 0;
+	u32 val, *m_reg;
+
 
 	/* no recursive mappings */
 	BUG_ON(overlay->virt_addr);
@@ -194,6 +200,30 @@ static struct overlay_registers *intel_overlay_map_regs_atomic(struct intel_over
 	} else
 		regs = overlay->reg_bo->phys_obj->handle->vaddr;
 
+	/* cludge to work around the first map */
+	if (overlay_map_counter < 2)
+		goto out;
+
+	m_reg = (u32 *) regs;
+	for (i = 0; i < OVERLAY_REGFILE_SIZE; i += 4) {
+		val = I915_READ(OVERLAY_REGFILE_START + i);
+		if (val != m_reg[i/4]) {
+			bad = 1;
+			printk("0x%04x value doesn't match (0x%x != 0x%x)\n",
+					i, val, m_reg[i/4]);
+		}
+	}
+
+	if (bad)
+		printk("inconsistent overlay regs in mapping %i\n",
+				overlay_map_counter);
+	else
+		printk("consistent overlay regs in mapping %i\n",
+				overlay_map_counter);
+
+out:
+	overlay_map_counter++;
+
 	return overlay->virt_addr = regs;
 }
 
@@ -851,6 +881,8 @@ int intel_overlay_switch_off(struct intel_overlay *overlay)
 	regs->OCMD = 0;
 	intel_overlay_unmap_regs_atomic(overlay);
 
+	printk("switching overlay off: inconsistent regs expected\n");
+
 	ret = intel_overlay_off(overlay);
 	if (ret != 0)
 		return ret;
@@ -1304,6 +1336,8 @@ int intel_overlay_attrs(struct drm_device *dev, void *data,
 
 		intel_overlay_unmap_regs_atomic(overlay);
 
+		printk("async attribute update: overlay inconsistency expected\n");
+
 		if (attrs->flags & I915_OVERLAY_UPDATE_GAMMA) {
 			if (!IS_I9XX(dev)) {
 				ret = -EINVAL;