+ /*
+ * 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;
+ }
+