FreeBSD 11-CURRENT r277961 i915_debug.c.patch

--- sys/dev/drm2/i915/i915_debug.c.orig (revision 277487)
+++ sys/dev/drm2/i915/i915_debug.c      (working copy)
@@ -1590,6 +1590,40 @@
    return (0);
 }

+static int
+i915_backlight(SYSCTL_HANDLER_ARGS)
+{
+   struct drm_device *dev;
+   drm_i915_private_t *dev_priv;
+   int error;
+   u32 val, min, 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 = 0.5 + val * 100.0 / max;
+   error = sysctl_handle_int(oidp, &val, 0, req);
+   if (error || !req->newptr)
+       return (error);
+   min = 0.5 + 0.5 * max / 100.0;  // 0.5%
+   val = 0.5 + val * max / 100.0;
+   if (val < min)
+       val = min;
+   else if (val > max)
+       val = max;
+   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);
@@ -1753,7 +1787,12 @@
        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)
        return (error);