ALSA: ASoC Blackfin: fix bug - Audio Latency on AD1981 with MMAP enabled

With MMAP enabled (DMA mode) on the AD1981, there is +/- 250ms of delay between
writing data to alsa and audio starts coming out of the AD1981.

Copy more data to local buffer before starting DMA

Signed-off-by: Cliff Cai <cliff.cai@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 35 insertions, 7 deletions

diff --git a/sound/soc/blackfin/bf5xx-ac97-pcm.c b/sound/soc/blackfin/bf5xx-ac97-pcm.c
index 51f4907c4831..25e50d2ea1ec 100644
--- a/sound/soc/blackfin/bf5xx-ac97-pcm.c
+++ b/sound/soc/blackfin/bf5xx-ac97-pcm.c
@@ -56,6 +56,7 @@ static void bf5xx_mmap_copy(struct snd_pcm_substream *substream,
                 sport->tx_pos += runtime->period_size;
                 if (sport->tx_pos >= runtime->buffer_size)
                         sport->tx_pos %= runtime->buffer_size;
+                sport->tx_delay_pos = sport->tx_pos;
         } else {
                 bf5xx_ac97_to_pcm(
                         (struct ac97_frame *)sport->rx_dma_buf + sport->rx_pos,
@@ -72,7 +73,15 @@ static void bf5xx_dma_irq(void *data)
         struct snd_pcm_substream *pcm = data;
 #if defined(CONFIG_SND_MMAP_SUPPORT)
         struct snd_pcm_runtime *runtime = pcm->runtime;
+        struct sport_device *sport = runtime->private_data;
         bf5xx_mmap_copy(pcm, runtime->period_size);
+        if (pcm->stream == SNDRV_PCM_STREAM_PLAYBACK) {
+                if (sport->once == 0) {
+                        snd_pcm_period_elapsed(pcm);
+                        bf5xx_mmap_copy(pcm, runtime->period_size);
+                        sport->once = 1;
+                }
+        }
 #endif
         snd_pcm_period_elapsed(pcm);
 }
@@ -114,6 +123,10 @@ static int bf5xx_pcm_hw_params(struct snd_pcm_substream *substream,
 
 static int bf5xx_pcm_hw_free(struct snd_pcm_substream *substream)
 {
+        struct snd_pcm_runtime *runtime = substream->runtime;
+
+        if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+        memset(runtime->dma_area, 0, runtime->buffer_size);
         snd_pcm_lib_free_pages(substream);
         return 0;
 }
@@ -127,16 +140,11 @@ static int bf5xx_pcm_prepare(struct snd_pcm_substream *substream)
          * SPORT working in TMD mode(include AC97).
          */
 #if defined(CONFIG_SND_MMAP_SUPPORT)
-        size_t size = bf5xx_pcm_hardware.buffer_bytes_max
-                        * sizeof(struct ac97_frame) / 4;
-        /*clean up intermediate buffer*/
         if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
-                memset(sport->tx_dma_buf, 0, size);
                 sport_set_tx_callback(sport, bf5xx_dma_irq, substream);
                 sport_config_tx_dma(sport, sport->tx_dma_buf, runtime->periods,
                         runtime->period_size * sizeof(struct ac97_frame));
         } else {
-                memset(sport->rx_dma_buf, 0, size);
                 sport_set_rx_callback(sport, bf5xx_dma_irq, substream);
                 sport_config_rx_dma(sport, sport->rx_dma_buf, runtime->periods,
                         runtime->period_size * sizeof(struct ac97_frame));
@@ -164,8 +172,12 @@ static int bf5xx_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
         pr_debug("%s enter\n", __func__);
         switch (cmd) {
         case SNDRV_PCM_TRIGGER_START:
-                if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+                if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
+                        bf5xx_mmap_copy(substream, runtime->period_size);
+                        snd_pcm_period_elapsed(substream);
+                        sport->tx_delay_pos = 0;
                         sport_tx_start(sport);
+                }
                 else
                         sport_rx_start(sport);
                 break;
@@ -198,7 +210,7 @@ static snd_pcm_uframes_t bf5xx_pcm_pointer(struct snd_pcm_substream *substream)
 
 #if defined(CONFIG_SND_MMAP_SUPPORT)
         if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
-                curr = sport->tx_pos;
+                curr = sport->tx_delay_pos;
         else
                 curr = sport->rx_pos;
 #else
@@ -237,6 +249,21 @@ static int bf5xx_pcm_open(struct snd_pcm_substream *substream)
         return ret;
 }
 
+static int bf5xx_pcm_close(struct snd_pcm_substream *substream)
+{
+        struct snd_pcm_runtime *runtime = substream->runtime;
+        struct sport_device *sport = runtime->private_data;
+
+        pr_debug("%s enter\n", __func__);
+        if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
+                sport->once = 0;
+                memset(sport->tx_dma_buf, 0, runtime->buffer_size * sizeof(struct ac97_frame));
+        } else
+                memset(sport->rx_dma_buf, 0, runtime->buffer_size * sizeof(struct ac97_frame));
+
+        return 0;
+}
+
 #ifdef CONFIG_SND_MMAP_SUPPORT
 static int bf5xx_pcm_mmap(struct snd_pcm_substream *substream,
         struct vm_area_struct *vma)
@@ -272,6 +299,7 @@ static	int bf5xx_pcm_copy(struct snd_pcm_substream *substream, int channel,
 
 struct snd_pcm_ops bf5xx_pcm_ac97_ops = {
         .open           = bf5xx_pcm_open,
+        .close          = bf5xx_pcm_close,
         .ioctl          = snd_pcm_lib_ioctl,
         .hw_params      = bf5xx_pcm_hw_params,
         .hw_free        = bf5xx_pcm_hw_free,