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[RFC,14/26] dmaengine: omap-dma: move barrier to omap_dma_start_desc()

Message ID E1VyjvT-0005Es-6A@rmk-PC.arm.linux.org.uk (mailing list archive)
State Accepted
Commit 59871902703c
Headers show

Commit Message

Russell King Jan. 2, 2014, 3:11 p.m. UTC 
We don't need to issue a barrier for every segment of a DMA transfer;
doing this just once per descriptor will do.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
---
 drivers/dma/omap-dma.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)
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Patch

diff --git a/drivers/dma/omap-dma.c b/drivers/dma/omap-dma.c
index bdea85802b5b..e212e0df9b42 100644
--- a/drivers/dma/omap-dma.c
+++ b/drivers/dma/omap-dma.c
@@ -194,7 +194,6 @@  static void omap_dma_start(struct omap_chan *c, struct omap_desc *d)
 
 	val = c->plat->dma_read(CCR, c->dma_ch);
 	val |= CCR_ENABLE;
-	mb();
 	c->plat->dma_write(val, CCR, c->dma_ch);
 }
 
@@ -301,6 +300,13 @@  static void omap_dma_start_desc(struct omap_chan *c)
 	c->desc = d = to_omap_dma_desc(&vd->tx);
 	c->sgidx = 0;
 
+	/*
+	 * This provides the necessary barrier to ensure data held in
+	 * DMA coherent memory is visible to the DMA engine prior to
+	 * the transfer starting.
+	 */
+	mb();
+
 	c->plat->dma_write(d->ccr, CCR, c->dma_ch);
 	if (dma_omap1())
 		c->plat->dma_write(d->ccr >> 16, CCR2, c->dma_ch);