ASoC: davinci-pcm: fix audible glitch on 2nd ping-pong playback

The release of the dma channels was being performed in prepare and there was a
edma_resume call for the asp-channel only being executed on START, RESUME and
PAUSE_RELEASE.

The mcasp on da850evm with ping-pong buffers enabled was exhibiting an audible
glitch on every playback after the first. It was determined through trial and
error that the following two changes fix this problem:

1) Move the edma_start calls from prepare to trigger and 2) reverse the order
of starting the asp and ram channels.

Signed-off-by: Ben Gardiner <bengardiner@nanometrics.ca>
Reviewed-by: Steven Faludi <stevenfaludi@nanometrics.ca>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

diff --git a/sound/soc/davinci/davinci-pcm.c b/sound/soc/davinci/davinci-pcm.c
index 9b5a9bf9393afd2d4f5d33e6014d3e30b7dfb377..5d9269a5176184ef79144ce6f9cef1ebfac3f1e1 100644 (file)
--- a/sound/soc/davinci/davinci-pcm.c
+++ b/sound/soc/davinci/davinci-pcm.c
@@ -544,6 +544,13 @@ static int davinci_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
 
        switch (cmd) {
        case SNDRV_PCM_TRIGGER_START:
+               edma_start(prtd->asp_channel);
+               if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
+                   prtd->ram_channel >= 0) {
+                       /* copy 1st iram buffer */
+                       edma_start(prtd->ram_channel);
+               }
+               break;
        case SNDRV_PCM_TRIGGER_RESUME:
        case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
                edma_resume(prtd->asp_channel);
@@ -582,11 +589,6 @@ static int davinci_pcm_prepare(struct snd_pcm_substream *substream)
                print_buf_info(prtd->asp_link[0], "asp_link[0]");
                print_buf_info(prtd->asp_link[1], "asp_link[1]");
 
-               if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
-                       /* copy 1st iram buffer */
-                       edma_start(prtd->ram_channel);
-               }
-               edma_start(prtd->asp_channel);
                return 0;
        }
        prtd->period = 0;
@@ -596,7 +598,6 @@ static int davinci_pcm_prepare(struct snd_pcm_substream *substream)
        edma_read_slot(prtd->asp_link[0], &prtd->asp_params);
        edma_write_slot(prtd->asp_channel, &prtd->asp_params);
        davinci_pcm_enqueue_dma(substream);
-       edma_start(prtd->asp_channel);
 
        return 0;
 }