ASoC: DaVinci: i2s, reduce underruns by combining into 1 element

Allow the left and right 16 bit samples to be shifted out as 1
32 bit sample.

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

1 files changed, 55 insertions, 19 deletions

diff --git a/sound/soc/davinci/davinci-i2s.c b/sound/soc/davinci/davinci-i2s.c
index d336786683b4..b2a5372ef72c 100644
--- a/sound/soc/davinci/davinci-i2s.c
+++ b/sound/soc/davinci/davinci-i2s.c
@@ -97,6 +97,23 @@ enum {
         DAVINCI_MCBSP_WORD_32,
 };
 
+static const unsigned char data_type[SNDRV_PCM_FORMAT_S32_LE + 1] = {
+        [SNDRV_PCM_FORMAT_S8]           = 1,
+        [SNDRV_PCM_FORMAT_S16_LE]       = 2,
+        [SNDRV_PCM_FORMAT_S32_LE]       = 4,
+};
+
+static const unsigned char asp_word_length[SNDRV_PCM_FORMAT_S32_LE + 1] = {
+        [SNDRV_PCM_FORMAT_S8]           = DAVINCI_MCBSP_WORD_8,
+        [SNDRV_PCM_FORMAT_S16_LE]       = DAVINCI_MCBSP_WORD_16,
+        [SNDRV_PCM_FORMAT_S32_LE]       = DAVINCI_MCBSP_WORD_32,
+};
+
+static const unsigned char double_fmt[SNDRV_PCM_FORMAT_S32_LE + 1] = {
+        [SNDRV_PCM_FORMAT_S8]           = SNDRV_PCM_FORMAT_S16_LE,
+        [SNDRV_PCM_FORMAT_S16_LE]       = SNDRV_PCM_FORMAT_S32_LE,
+};
+
 struct davinci_mcbsp_dev {
         struct davinci_pcm_dma_params   dma_params[2];
         void __iomem                    *base;
@@ -105,6 +122,27 @@ struct davinci_mcbsp_dev {
         int                             mode;
         u32                             pcr;
         struct clk                      *clk;
+        /*
+         * Combining both channels into 1 element will at least double the
+         * amount of time between servicing the dma channel, increase
+         * effiency, and reduce the chance of overrun/underrun. But,
+         * it will result in the left & right channels being swapped.
+         *
+         * If relabeling the left and right channels is not possible,
+         * you may want to let the codec know to swap them back.
+         *
+         * It may allow x10 the amount of time to service dma requests,
+         * if the codec is master and is using an unnecessarily fast bit clock
+         * (ie. tlvaic23b), independent of the sample rate. So, having an
+         * entire frame at once means it can be serviced at the sample rate
+         * instead of the bit clock rate.
+         *
+         * In the now unlikely case that an underrun still
+         * occurs, both the left and right samples will be repeated
+         * so that no pops are heard, and the left and right channels
+         * won't end up being swapped because of the underrun.
+         */
+        unsigned enable_channel_combine:1;
 };
 
 static inline void davinci_mcbsp_write_reg(struct davinci_mcbsp_dev *dev,
@@ -344,6 +382,8 @@ static int davinci_i2s_hw_params(struct snd_pcm_substream *substream,
         int mcbsp_word_length;
         unsigned int rcr, xcr, srgr;
         u32 spcr;
+        snd_pcm_format_t fmt;
+        unsigned element_cnt = 1;
 
         /* general line settings */
         spcr = davinci_mcbsp_read_reg(dev, DAVINCI_MCBSP_SPCR_REG);
@@ -373,29 +413,24 @@ static int davinci_i2s_hw_params(struct snd_pcm_substream *substream,
                 xcr |= DAVINCI_MCBSP_XCR_XDATDLY(1);
         }
         /* Determine xfer data type */
-        switch (params_format(params)) {
-        case SNDRV_PCM_FORMAT_S8:
-                dma_params->data_type = 1;
-                mcbsp_word_length = DAVINCI_MCBSP_WORD_8;
-                break;
-        case SNDRV_PCM_FORMAT_S16_LE:
-                dma_params->data_type = 2;
-                mcbsp_word_length = DAVINCI_MCBSP_WORD_16;
-                break;
-        case SNDRV_PCM_FORMAT_S32_LE:
-                dma_params->data_type = 4;
-                mcbsp_word_length = DAVINCI_MCBSP_WORD_32;
-                break;
-        default:
+        fmt = params_format(params);
+        if ((fmt > SNDRV_PCM_FORMAT_S32_LE) || !data_type[fmt]) {
                 printk(KERN_WARNING "davinci-i2s: unsupported PCM format\n");
                 return -EINVAL;
         }
 
-        dma_params->acnt  = dma_params->data_type;
+        if (params_channels(params) == 2) {
+                element_cnt = 2;
+                if (double_fmt[fmt] && dev->enable_channel_combine) {
+                        element_cnt = 1;
+                        fmt = double_fmt[fmt];
+                }
+        }
+        dma_params->acnt = dma_params->data_type = data_type[fmt];
         dma_params->fifo_level = 0;
-
-        rcr |= DAVINCI_MCBSP_RCR_RFRLEN1(1);
-        xcr |= DAVINCI_MCBSP_XCR_XFRLEN1(1);
+        mcbsp_word_length = asp_word_length[fmt];
+        rcr |= DAVINCI_MCBSP_RCR_RFRLEN1(element_cnt - 1);
+        xcr |= DAVINCI_MCBSP_XCR_XFRLEN1(element_cnt - 1);
 
         rcr |= DAVINCI_MCBSP_RCR_RWDLEN1(mcbsp_word_length) |
                 DAVINCI_MCBSP_RCR_RWDLEN2(mcbsp_word_length);
@@ -510,7 +545,8 @@ static int davinci_i2s_probe(struct platform_device *pdev)
                 ret = -ENOMEM;
                 goto err_release_region;
         }
-
+        if (pdata)
+                dev->enable_channel_combine = pdata->enable_channel_combine;
         dev->clk = clk_get(&pdev->dev, NULL);
         if (IS_ERR(dev->clk)) {
                 ret = -ENODEV;