Index: i915/i915_debug.c
===================================================================
--- i915/i915_debug.c	(revision 277875)
+++ i915/i915_debug.c	(working copy)
@@ -724,7 +724,7 @@
 
 	for (i = 0; i < DRM_ARRAY_SIZE(error->ring); i++) {
 		struct drm_i915_error_object *obj;
- 
+
 		if ((obj = error->ring[i].batchbuffer)) {
 			sbuf_printf(m, "%s --- gtt_offset = 0x%08x\n",
 				   dev_priv->rings[i].name,
@@ -1590,6 +1590,38 @@
 	return (0);
 }
 
+// NB - only works when y != 0!
+#define U_CEIL_DIV(x, y) ((x) + (y) - 1) / (y)
+
+static int
+i915_backlight(SYSCTL_HANDLER_ARGS)
+{
+	struct drm_device *dev;
+	drm_i915_private_t *dev_priv;
+	int error;
+	u32 val, max;
+
+	dev = arg1;
+	dev_priv = dev->dev_private;
+	if(dev_priv == NULL)
+		return (EBUSY);
+	DRM_LOCK(dev);
+	val = intel_panel_get_backlight(dev);
+	max = intel_panel_get_max_backlight(dev);
+	DRM_UNLOCK(dev);
+
+	// XXX specific devices, works fine on ivy bridge though
+	val = (val * 100) / max;
+	error = sysctl_handle_int(oidp, &val, 0, req);
+	if (error || !req->newptr)
+		return (error);
+	val = U_CEIL_DIV(max * val, 100);
+	DRM_LOCK(dev);
+	intel_panel_set_backlight(dev, val);
+	DRM_UNLOCK(dev);
+	return (0);
+}
+
 static struct i915_info_sysctl_list {
 	const char *name;
 	int (*ptr)(struct drm_device *dev, struct sbuf *m, void *data);
@@ -1753,6 +1785,11 @@
 	    CTLFLAG_RW, &i915_intr_pf, 0, NULL);
 	if (oid == NULL)
 		return (ENOMEM);
+	oid = SYSCTL_ADD_PROC(ctx, SYSCTL_CHILDREN(top), OID_AUTO,
+	    "i915_backlight", CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE, dev,
+	    0, i915_backlight, "I", NULL);
+	if (oid == NULL)
+		return (ENOMEM);
 
 	error = drm_add_busid_modesetting(dev, ctx, top);
 	if (error != 0)
@@ -1764,6 +1801,5 @@
 void
 i915_sysctl_cleanup(struct drm_device *dev)
 {
-
 	free(dev->sysctl_private, DRM_MEM_DRIVER);
 }