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>

diff --git a/arch/arm/mach-davinci/include/mach/asp.h b/arch/arm/mach-davinci/include/mach/asp.h
index 18e4ce3..019c647 100644 (file)
--- a/arch/arm/mach-davinci/include/mach/asp.h
+++ b/arch/arm/mach-davinci/include/mach/asp.h
@@ -51,6 +51,12 @@ struct snd_platform_data {
        u32 rx_dma_offset;
        enum dma_event_q eventq_no;     /* event queue number */
        unsigned int codec_fmt;
+       /*
+        * Allowing this is more efficient and eliminates left and right swaps
+        * caused by underruns, but will swap the left and right channels
+        * when compared to previous behavior.
+        */
+       unsigned enable_channel_combine:1;
 
        /* McASP specific fields */
        int tdm_slots;

diff --git a/sound/soc/davinci/davinci-i2s.c b/sound/soc/davinci/davinci-i2s.c
index d336786..b2a5372 100644 (file)
--- 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;