[RFC] [PATCH 3/3] ASoC: OMAP: Enhance OMAP1510 DMA progress software counter

[Janusz Krzysztofik]

Enhance period index accuracy, particularly just before buffer rewind, by
making use of DMA interrupt status flags in addition to simply counting
interrupts

This patch applies on top of patch 2 from this series:
[RFC][PATCH 2/3] ASoC: OMAP: Make use of DMA channel self linking on OMAP1510

Created against linux-2.6.31-rc5.

Tested on Amstrad Delta.

Signed-off-by: Janusz Krzysztofik <jkrzyszt@xxxxxxxxxxxx>

---
--- linux-2.6.31-rc5/sound/soc/omap/omap-pcm.c.orig	2009-08-10 08:31:08.000000000 +0200
+++ linux-2.6.31-rc5/sound/soc/omap/omap-pcm.c	2009-08-10 08:55:09.000000000 +0200
@@ -68,13 +68,28 @@ static void omap_pcm_dma_irq(int ch, u16
 		 * that can be used by omap_pcm_pointer() instead.
 		 */
 		spin_lock_irqsave(&prtd->lock, flags);
-		if (prtd->period_index >= 0) {
-			if (++prtd->period_index == runtime->periods) {
+		if (stat & OMAP_DMA_LAST_IRQ) {
+			/* last period of a buffer has been started */
+			if (prtd->period_index == (runtime->periods - 1)) {
+				/* we are in sync, do nothing */
+				spin_unlock_irqrestore(&prtd->lock, flags);
+				return;
+			} else if (prtd->period_index >= 0) {
+				/* possible IRQ loss, update the pointer */
+				prtd->period_index = runtime->periods - 1;
+			}
+		} else if (prtd->period_index >= 0) {
+			/* playback in progress - increment the counter,
+			 * check for end of buffer */
+			if ((++prtd->period_index >= runtime->periods) ||
+						(stat & OMAP_DMA_BLOCK_IRQ)) {
+				/* end of buffer reached, loop back */
 				prtd->period_index = 0;
 			}
 		}
 		spin_unlock_irqrestore(&prtd->lock, flags);
-	}
+	} else if (stat & OMAP_DMA_LAST_IRQ)
+		return;
 
 	snd_pcm_period_elapsed(substream);
 }
@@ -175,7 +190,8 @@ static int omap_pcm_prepare(struct snd_p
 	dma_params.frame_count	= runtime->periods;
 	omap_set_dma_params(prtd->dma_ch, &dma_params);
 
-	omap_enable_dma_irq(prtd->dma_ch, OMAP_DMA_FRAME_IRQ);
+	omap_enable_dma_irq(prtd->dma_ch, OMAP_DMA_FRAME_IRQ |
+				(cpu_is_omap1510() ? OMAP_DMA_LAST_IRQ : 0));
 
 	return 0;
 }
--
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