ALSA: hda - hdmi add wmb barrier for audio component

BugLink: http://bugs.launchpad.net/bugs/1596871

To make sure audio_ptr is set before intel_audio_codec_enable()
or intel_audio_codec_disable() calling pin_eld_notify(),
this patch adds wmb barrier to prevent optimizing.
Signed-off-by: Libin Yang <libin.yang@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
(cherry picked from commit ec75a940)
Signed-off-by: Hui Wang <hui.wang@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

sound/pci/hda/patch_hdmi.c

@@ -2401,6 +2401,11 @@ static int patch_generic_hdmi(struct hda_codec *codec)
 	if (is_haswell_plus(codec) || is_valleyview_plus(codec)) {
 		codec->depop_delay = 0;
 		spec->i915_audio_ops.audio_ptr = codec;
+		/* intel_audio_codec_enable() or intel_audio_codec_disable()
+		 * will call pin_eld_notify with using audio_ptr pointer
+		 * We need make sure audio_ptr is really setup
+		 */
+		wmb();
 		spec->i915_audio_ops.pin_eld_notify = intel_pin_eld_notify;
 		snd_hdac_i915_register_notifier(&spec->i915_audio_ops);
 	}