ASoC: DaVinci: Audio: Fix swapping of channels at start of stereo playback

Fixes swapping of channels at start of stereo playback.

Channel swap can be observed while playing left-only or right-only audio data. The channel
swap is fixed by handling the XSYNCERR condition.

Signed-off-by: Naresh Medisetty <naresh@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

1 files changed, 46 insertions, 3 deletions

diff --git a/sound/soc/davinci/davinci-i2s.c b/sound/soc/davinci/davinci-i2s.c
index d814ec8947e5..8c1bf876031d 100644
--- a/sound/soc/davinci/davinci-i2s.c
+++ b/sound/soc/davinci/davinci-i2s.c
@@ -111,16 +111,59 @@ static void davinci_mcbsp_start(struct snd_pcm_substream *substream)
 {
         struct snd_soc_pcm_runtime *rtd = substream->private_data;
         struct davinci_mcbsp_dev *dev = rtd->dai->cpu_dai->private_data;
+        struct snd_soc_device *socdev = rtd->socdev;
+        struct snd_soc_platform *platform = socdev->platform;
         u32 w;
+        int ret;
 
         /* Start the sample generator and enable transmitter/receiver */
         w = davinci_mcbsp_read_reg(dev, DAVINCI_MCBSP_SPCR_REG);
         MOD_REG_BIT(w, DAVINCI_MCBSP_SPCR_GRST, 1);
-        if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+        davinci_mcbsp_write_reg(dev, DAVINCI_MCBSP_SPCR_REG, w);
+
+        if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
+                /* Stop the DMA to avoid data loss */
+                /* while the transmitter is out of reset to handle XSYNCERR */
+                if (platform->pcm_ops->trigger) {
+                        ret = platform->pcm_ops->trigger(substream,
+                                SNDRV_PCM_TRIGGER_STOP);
+                        if (ret < 0)
+                                printk(KERN_DEBUG "Playback DMA stop failed\n");
+                }
+
+                /* Enable the transmitter */
+                w = davinci_mcbsp_read_reg(dev, DAVINCI_MCBSP_SPCR_REG);
                 MOD_REG_BIT(w, DAVINCI_MCBSP_SPCR_XRST, 1);
-        else
+                davinci_mcbsp_write_reg(dev, DAVINCI_MCBSP_SPCR_REG, w);
+
+                /* wait for any unexpected frame sync error to occur */
+                udelay(100);
+
+                /* Disable the transmitter to clear any outstanding XSYNCERR */
+                w = davinci_mcbsp_read_reg(dev, DAVINCI_MCBSP_SPCR_REG);
+                MOD_REG_BIT(w, DAVINCI_MCBSP_SPCR_XRST, 0);
+                davinci_mcbsp_write_reg(dev, DAVINCI_MCBSP_SPCR_REG, w);
+
+                /* Restart the DMA */
+                if (platform->pcm_ops->trigger) {
+                        ret = platform->pcm_ops->trigger(substream,
+                                SNDRV_PCM_TRIGGER_START);
+                        if (ret < 0)
+                                printk(KERN_DEBUG "Playback DMA start failed\n");
+                }
+                /* Enable the transmitter */
+                w = davinci_mcbsp_read_reg(dev, DAVINCI_MCBSP_SPCR_REG);
+                MOD_REG_BIT(w, DAVINCI_MCBSP_SPCR_XRST, 1);
+                davinci_mcbsp_write_reg(dev, DAVINCI_MCBSP_SPCR_REG, w);
+
+        } else {
+
+                /* Enable the reciever */
+                w = davinci_mcbsp_read_reg(dev, DAVINCI_MCBSP_SPCR_REG);
                 MOD_REG_BIT(w, DAVINCI_MCBSP_SPCR_RRST, 1);
-        davinci_mcbsp_write_reg(dev, DAVINCI_MCBSP_SPCR_REG, w);
+                davinci_mcbsp_write_reg(dev, DAVINCI_MCBSP_SPCR_REG, w);
+        }
+
 
         /* Start frame sync */
         w = davinci_mcbsp_read_reg(dev, DAVINCI_MCBSP_SPCR_REG);