drm/i915: mask the video DIP port select

Should prevent bugs when changing the port.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 833052e..71e7af9 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -1700,6 +1700,7 @@
 #define   VIDEO_DIP_ENABLE		(1 << 31)
 #define   VIDEO_DIP_PORT_B		(1 << 29)
 #define   VIDEO_DIP_PORT_C		(2 << 29)
+#define   VIDEO_DIP_PORT_MASK		(3 << 29)
 #define   VIDEO_DIP_ENABLE_AVI		(1 << 21)
 #define   VIDEO_DIP_ENABLE_VENDOR	(2 << 21)
 #define   VIDEO_DIP_ENABLE_SPD		(8 << 21)
diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
index af88313..952eaf7 100644
--- a/drivers/gpu/drm/i915/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/intel_hdmi.c
@@ -125,6 +125,7 @@
 
 
 	/* XXX first guess at handling video port, is this corrent? */
+	val &= ~VIDEO_DIP_PORT_MASK;
 	if (intel_hdmi->sdvox_reg == SDVOB)
 		val |= VIDEO_DIP_PORT_B;
 	else if (intel_hdmi->sdvox_reg == SDVOC)