drm/i915: Write the SDVO reg twice on IBX

On IBX the SDVO/HDMI register write may be masked when enabling the
port, so it may need to written twice. The HDMI code does this, but
the SDVO code does not. Add the workaround to the SDVO code as well.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_sdvo.c

@@ -243,6 +243,14 @@ static void intel_sdvo_write_sdvox(struct intel_sdvo *intel_sdvo, u32 val)
 	if (intel_sdvo->sdvo_reg == PCH_SDVOB) {
 		I915_WRITE(intel_sdvo->sdvo_reg, val);
 		POSTING_READ(intel_sdvo->sdvo_reg);
+		/*
+		 * HW workaround, need to write this twice for issue
+		 * that may result in first write getting masked.
+		 */
+		if (HAS_PCH_IBX(dev)) {
+			I915_WRITE(intel_sdvo->sdvo_reg, val);
+			POSTING_READ(intel_sdvo->sdvo_reg);
+		}
 		return;
 	}