drm/i915: Disable DDI Pipe Control on HSW while disabling pipe

[Shobhit Kumar <shobhit.kumar@intel.com>]

In Haswell while disabling a pipe, we need to disable the DDI control as
well along with the PIPECONF. Otherwise we will hit assertions during crtc
disable

Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
---
 drivers/gpu/drm/i915/intel_display.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 0161d94..c69671d 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -1645,6 +1645,13 @@ static void intel_disable_pipe(struct drm_i915_private *dev_priv,
 
 	I915_WRITE(reg, val & ~PIPECONF_ENABLE);
 	intel_wait_for_pipe_off(dev_priv->dev, pipe);
+
+	/* On HSW DDI Pipe control has to be disabled as well */
+	if (IS_HASWELL(dev_priv->dev)) {
+		val = I915_READ(DDI_FUNC_CTL(pipe));
+		val = val  & (~PIPE_DDI_FUNC_ENABLE);
+		I915_WRITE(DDI_FUNC_CTL(pipe), val);
+	}
 }
 
 /*
-- 
1.7.7.6