ALSA: x86: hdmi: continue playback even when display resolution changes

When the display resolution changes, the drm disables the
display pipes due to which audio rendering stops. At this
time, we need to ensure the existing audio pointers and
buffers are cleared out so that the playback can restarted
once the display pipe is enabled with a different N/CTS values

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Jerome Anand <jerome.anand@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/x86/intel_hdmi_audio.c

@@ -43,6 +43,7 @@ static DEFINE_MUTEX(had_mutex);
 static int hdmi_card_index = SNDRV_DEFAULT_IDX1;
 static char *hdmi_card_id = SNDRV_DEFAULT_STR1;
 static struct snd_intelhad *had_data;
+static int underrun_count;
 
 module_param_named(index, hdmi_card_index, int, 0444);
 MODULE_PARM_DESC(index,
@@ -1052,6 +1053,7 @@ static int snd_intelhad_open(struct snd_pcm_substream *substream)
 	intelhaddata = snd_pcm_substream_chip(substream);
 	had_stream = intelhaddata->private_data;
 	runtime = substream->runtime;
+	underrun_count = 0;
 
 	pm_runtime_get(intelhaddata->dev);
 
@@ -1445,10 +1447,23 @@ static snd_pcm_uframes_t snd_intelhad_pcm_pointer(
 
 	buf_id = intelhaddata->curr_buf % 4;
 	had_read_register(AUD_BUF_A_LENGTH + (buf_id * HAD_REG_WIDTH), &t);
-	if (t == 0) {
-		pr_debug("discovered buffer done for buf %d\n", buf_id);
-		/* had_process_buffer_done(intelhaddata); */
+
+	if ((t == 0) || (t == ((u32)-1L))) {
+		underrun_count++;
+		pr_debug("discovered buffer done for buf %d, count = %d\n",
+			buf_id, underrun_count);
+
+		if (underrun_count > (HAD_MIN_PERIODS/2)) {
+			pr_debug("assume audio_codec_reset, underrun = %d - do xrun\n",
+				underrun_count);
+			underrun_count = 0;
+			return SNDRV_PCM_POS_XRUN;
+		}
+	} else {
+		/* Reset Counter */
+		underrun_count = 0;
 	}
+
 	t = intelhaddata->buf_info[buf_id].buf_size - t;
 
 	if (intelhaddata->stream_info.buffer_rendered)