drm/i915: add missing SDVO bits for interlaced modes on ILK

This was pointed by Jesse Barnes. The code now seems to follow the
specification but I don't have an SDVO device to really test this.
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -3365,6 +3365,7 @@
 #define  TRANS_INTERLACE_MASK   (7<<21)
 #define  TRANS_PROGRESSIVE      (0<<21)
 #define  TRANS_INTERLACED       (3<<21)
+#define  TRANS_LEGACY_INTERLACED_ILK (2<<21)
 #define  TRANS_8BPC             (0<<5)
 #define  TRANS_10BPC            (1<<5)
 #define  TRANS_6BPC             (2<<5)

drivers/gpu/drm/i915/intel_display.c

@@ -1267,6 +1267,7 @@ static void intel_enable_transcoder(struct drm_i915_private *dev_priv,
 {
 	int reg;
 	u32 val, pipeconf_val;
+	struct drm_crtc *crtc = dev_priv->pipe_to_crtc_mapping[pipe];
 
 	/* PCH only available on ILK+ */
 	BUG_ON(dev_priv->info->gen < 5);
@@ -1293,6 +1294,10 @@ static void intel_enable_transcoder(struct drm_i915_private *dev_priv,
 
 	val &= ~TRANS_INTERLACE_MASK;
 	if ((pipeconf_val & PIPECONF_INTERLACE_MASK) == PIPECONF_INTERLACED_ILK)
+		if (HAS_PCH_IBX(dev_priv->dev) &&
+		    intel_pipe_has_type(crtc, INTEL_OUTPUT_SDVO))
+			val |= TRANS_LEGACY_INTERLACED_ILK;
+		else
 			val |= TRANS_INTERLACED;
 	else
 		val |= TRANS_PROGRESSIVE;