openwrt/target/linux/xburst/patches-3.3/0016-ASoC-JZ4740-Support-buffer-size-that-is-not-a-multip.patch

From 8a5087fe59e31efb8641e704058328997c3c8ff1 Mon Sep 17 00:00:00 2001
From: Maarten ter Huurne <maarten@treewalker.org>
Date: Wed, 10 Aug 2011 00:25:11 +0200
Subject: [PATCH 16/21] ASoC: JZ4740: Support buffer size that is not a
 multiple of period size.

This fixes glitches triggered by libao, which sets time-based intervals
instead of byte-based intervals like SDL does.

Thanks to Paul Cercueil for figuring out that the buffer size was causing
the glitches and to Lars Clausen for helping me write the fix.
---
 sound/soc/jz4740/jz4740-pcm.c |   21 ++++++++++++++++++---
 1 files changed, 18 insertions(+), 3 deletions(-)

--- a/sound/soc/jz4740/jz4740-pcm.c
+++ b/sound/soc/jz4740/jz4740-pcm.c
@@ -31,6 +31,7 @@
 
 struct jz4740_runtime_data {
 	unsigned long dma_period;
+	unsigned long dma_period_left;
 	dma_addr_t dma_start;
 	dma_addr_t dma_pos;
 	dma_addr_t dma_end;
@@ -67,10 +68,13 @@ static void jz4740_pcm_start_transfer(st
 	if (prtd->dma_pos == prtd->dma_end)
 		prtd->dma_pos = prtd->dma_start;
 
-	if (prtd->dma_pos + prtd->dma_period > prtd->dma_end)
+	if (prtd->dma_period_left == 0)
+		prtd->dma_period_left = prtd->dma_period;
+
+	if (prtd->dma_pos + prtd->dma_period_left > prtd->dma_end)
 		count = prtd->dma_end - prtd->dma_pos;
 	else
-		count = prtd->dma_period;
+		count = prtd->dma_period_left;
 
 	jz4740_dma_disable(prtd->dma);
 
@@ -85,6 +89,7 @@ static void jz4740_pcm_start_transfer(st
 	jz4740_dma_set_transfer_count(prtd->dma, count);
 
 	prtd->dma_pos += count;
+	prtd->dma_period_left -= count;
 
 	jz4740_dma_enable(prtd->dma);
 }
@@ -96,7 +101,8 @@ static void jz4740_pcm_dma_transfer_done
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	struct jz4740_runtime_data *prtd = runtime->private_data;
 
-	snd_pcm_period_elapsed(substream);
+	if (prtd->dma_period_left == 0)
+		snd_pcm_period_elapsed(substream);
 
 	jz4740_pcm_start_transfer(prtd, substream);
 }
@@ -133,6 +139,7 @@ static int jz4740_pcm_hw_params(struct s
 	runtime->dma_bytes = params_buffer_bytes(params);
 
 	prtd->dma_period = params_period_bytes(params);
+	prtd->dma_period_left = 0;
 	prtd->dma_start = runtime->dma_addr;
 	prtd->dma_pos = prtd->dma_start;
 	prtd->dma_end = prtd->dma_start + runtime->dma_bytes;
@@ -160,6 +167,7 @@ static int jz4740_pcm_prepare(struct snd
 	if (!prtd->dma)
 		return -EBUSY;
 
+	prtd->dma_period_left = 0;
 	prtd->dma_pos = prtd->dma_start;
 
 	return 0;
@@ -219,6 +227,13 @@ static int jz4740_pcm_open(struct snd_pc
 	if (prtd == NULL)
 		return -ENOMEM;
 
+	/* Force period and buffer size to be a multiple of the DMA transfer
+	 * size, which is 16 bytes. */
+	snd_pcm_hw_constraint_step(runtime, 0,
+				   SNDRV_PCM_HW_PARAM_PERIOD_BYTES, 16);
+	snd_pcm_hw_constraint_step(runtime, 0,
+				   SNDRV_PCM_HW_PARAM_BUFFER_BYTES, 16);
+
 	snd_soc_set_runtime_hwparams(substream, &jz4740_pcm_hardware);
 
 	runtime->private_data = prtd;