ASoC: DaVinci: pcm, fix underrun by using sram

Fix underruns by using dma to copy 1st to sram
in a ping/pong buffer style and then copying from
the sram to the ASP. This also has the advantage
of tolerating very long interrupt latency on dma
completion.
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>

arch/arm/mach-davinci/include/mach/asp.h

@@ -57,6 +57,8 @@ struct snd_platform_data {
 	 * when compared to previous behavior.
 	 */
 	unsigned enable_channel_combine:1;
+	unsigned sram_size_playback;
+	unsigned sram_size_capture;
 
 	/* McASP specific fields */
 	int tdm_slots;

sound/soc/davinci/davinci-i2s.c

@@ -545,8 +545,13 @@ static int davinci_i2s_probe(struct platform_device *pdev)
 		ret = -ENOMEM;
 		goto err_release_region;
 	}
-	if (pdata)
+	if (pdata) {
 		dev->enable_channel_combine = pdata->enable_channel_combine;
+		dev->dma_params[SNDRV_PCM_STREAM_PLAYBACK].sram_size =
+			pdata->sram_size_playback;
+		dev->dma_params[SNDRV_PCM_STREAM_CAPTURE].sram_size =
+			pdata->sram_size_capture;
+	}
 	dev->clk = clk_get(&pdev->dev, NULL);
 	if (IS_ERR(dev->clk)) {
 		ret = -ENODEV;

sound/soc/davinci/davinci-pcm.h

@@ -20,6 +20,7 @@ struct davinci_pcm_dma_params {
 	int channel;			/* sync dma channel ID */
 	unsigned short acnt;
 	dma_addr_t dma_addr;		/* device physical address for DMA */
+	unsigned sram_size;
 	enum dma_event_q eventq_no;	/* event queue number */
 	unsigned char data_type;	/* xfer data type */
 	unsigned char convert_mono_stereo;