drm/i915: enable/disable backlight for eDP

Like we already do for the LVDS panels. This seems to help greatly
in setting up the backlight, since the BIOS might refuse to cooperate.
Reviewed-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Tested-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>

v2: Move the backlight_off call from panel_off to edp_backlight_off,
noticed by Paulo Zanoni.
Reviewed-by: NPaulo Zanoni <przanoni@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_dp.c

@@ -1164,6 +1164,7 @@ static void ironlake_edp_backlight_on(struct intel_dp *intel_dp)
 {
 	struct drm_device *dev = intel_dp->base.base.dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
+	int pipe = to_intel_crtc(intel_dp->base.base.crtc)->pipe;
 	u32 pp;
 
 	if (!is_edp(intel_dp))
@@ -1181,6 +1182,8 @@ static void ironlake_edp_backlight_on(struct intel_dp *intel_dp)
 	pp |= EDP_BLC_ENABLE;
 	I915_WRITE(PCH_PP_CONTROL, pp);
 	POSTING_READ(PCH_PP_CONTROL);
+
+	intel_panel_enable_backlight(dev, pipe);
 }
 
 static void ironlake_edp_backlight_off(struct intel_dp *intel_dp)
@@ -1192,6 +1195,8 @@ static void ironlake_edp_backlight_off(struct intel_dp *intel_dp)
 	if (!is_edp(intel_dp))
 		return;
 
+	intel_panel_disable_backlight(dev);
+
 	DRM_DEBUG_KMS("\n");
 	pp = ironlake_get_pp_control(dev_priv);
 	pp &= ~EDP_BLC_ENABLE;