linux-kernel - [ 08/27] dmaengine: omap-dma: Start DMA without delay for cyclic channels

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Message-Id: <20130415024231.986725437@linuxfoundation.org>
Date:	Sun, 14 Apr 2013 19:43:07 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Peter Meerwald <pmeerw@...erw.net>,
	Peter Ujfalusi <peter.ujfalusi@...com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Vinod Koul <vinod.koul@...el.com>
Subject: [ 08/27] dmaengine: omap-dma: Start DMA without delay for cyclic channels

3.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Ujfalusi <peter.ujfalusi@...com>

commit 765024697807ad1e1cac332aa891253ca4a339da upstream.

cyclic DMA is only used by audio which needs DMA to be started without a
delay.
If the DMA for audio is started using the tasklet we experience random
channel switch (to be more precise: channel shift).

Reported-by: Peter Meerwald <pmeerw@...erw.net>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@...com>
Acked-by: Russell King <rmk+kernel@....linux.org.uk>
Signed-off-by: Vinod Koul <vinod.koul@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/dma/omap-dma.c |   20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

--- a/drivers/dma/omap-dma.c
+++ b/drivers/dma/omap-dma.c
@@ -276,12 +276,20 @@ static void omap_dma_issue_pending(struc
 
 	spin_lock_irqsave(&c->vc.lock, flags);
 	if (vchan_issue_pending(&c->vc) && !c->desc) {
-		struct omap_dmadev *d = to_omap_dma_dev(chan->device);
-		spin_lock(&d->lock);
-		if (list_empty(&c->node))
-			list_add_tail(&c->node, &d->pending);
-		spin_unlock(&d->lock);
-		tasklet_schedule(&d->task);
+		/*
+		 * c->cyclic is used only by audio and in this case the DMA need
+		 * to be started without delay.
+		 */
+		if (!c->cyclic) {
+			struct omap_dmadev *d = to_omap_dma_dev(chan->device);
+			spin_lock(&d->lock);
+			if (list_empty(&c->node))
+				list_add_tail(&c->node, &d->pending);
+			spin_unlock(&d->lock);
+			tasklet_schedule(&d->task);
+		} else {
+			omap_dma_start_desc(c);
+		}
 	}
 	spin_unlock_irqrestore(&c->vc.lock, flags);
 }


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