drm/i915: panel: invert brightness via quirk

A machine may need to invert the panel backlight brightness value. This
patch adds the infrastructure for a quirk to do so.

Signed-off-by: Carsten Emde <C.Emde@osadl.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 615b397..92208f8 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -9020,6 +9020,15 @@
 	dev_priv->quirks |= QUIRK_LVDS_SSC_DISABLE;
 }
 
+/*
+ * A machine may need to invert the panel backlight brightness value
+ */
+static void quirk_invert_brightness(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	dev_priv->quirks |= QUIRK_INVERT_BRIGHTNESS;
+}
+
 struct intel_quirk {
 	int device;
 	int subsystem_vendor;