ASoC: add start treshold to prevent underflows in some cases

[pandora-kernel.git] / sound / soc / omap / omap-pcm.c

diff --git a/sound/soc/omap/omap-pcm.c b/sound/soc/omap/omap-pcm.c
index e9084fd..b411eb4 100644 (file)
--- a/sound/soc/omap/omap-pcm.c
+++ b/sound/soc/omap/omap-pcm.c
@@ -168,6 +168,31 @@ static int omap_pcm_prepare(struct snd_pcm_substream *substream)
 
        omap_enable_dma_irq(prtd->dma_ch, OMAP_DMA_FRAME_IRQ);
 
+       /*
+        * To handle realtime streaming sources properly, we need to be sure
+        * we have at least 2 periods of size larger than FIFO in the buffer
+        * to start playing without underflowing. This is because DMA is always
+        * ahead of playback by amount close to FIFO size and needs to have
+        * next period ready when previous one finishes transfering to FIFO.
+        */
+       if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
+           runtime->periods > 1) {
+               struct snd_soc_pcm_runtime *rtd = substream->private_data;
+               int *mcbsp_bus_id = rtd->dai->cpu_dai->private_data;
+               int fifo_samples = (*mcbsp_bus_id == 1) ? 1024 : 256;
+               int period_samples, period_frames;
+               
+               period_samples = bytes_to_samples(runtime,
+                               snd_pcm_lib_period_bytes(substream));
+               if (period_samples < fifo_samples + runtime->channels)
+                       period_samples = fifo_samples + runtime->channels;
+               period_frames = bytes_to_frames(runtime,
+                               samples_to_bytes(runtime, period_samples)) * 2;
+
+               if (runtime->start_threshold < period_frames)
+                       runtime->start_threshold = period_frames;
+       }
+
        return 0;
 }
 
@@ -233,7 +258,7 @@ static int omap_pcm_open(struct snd_pcm_substream *substream)
        if (ret < 0)
                goto out;
 
-       prtd = kzalloc(sizeof(prtd), GFP_KERNEL);
+       prtd = kzalloc(sizeof(*prtd), GFP_KERNEL);
        if (prtd == NULL) {
                ret = -ENOMEM;
                goto out;