linux-kernel - [PATCH] DMA: add cpu_relax() to busy-loop in dma_sync

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Message-id: <201211081102.07811.b.zolnierkie@samsung.com>
Date:	Thu, 08 Nov 2012 11:02:07 +0100
From:	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:	linux-kernel@...r.kernel.org
Cc:	Vinod Koul <vinod.koul@...el.com>, Dan Williams <djbw@...com>,
	Tomasz Figa <t.figa@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>
Subject: [PATCH] DMA: add cpu_relax() to busy-loop in dma_sync_wait()

From: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: [PATCH] DMA: add cpu_relax() to busy-loop in dma_sync_wait()

Removal of the busy-loop from dma_sync_wait() is not a trivial
task so just add cpu_relax() to the loop for now.

Cc: Vinod Koul <vinod.koul@...el.com>
Cc: Dan Williams <djbw@...com>
Cc: Tomasz Figa <t.figa@...sung.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@...sung.com>
---
 drivers/dma/dmaengine.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Index: b/drivers/dma/dmaengine.c
===================================================================
--- a/drivers/dma/dmaengine.c	2012-11-07 16:12:41.776876102 +0100
+++ b/drivers/dma/dmaengine.c	2012-11-07 16:13:04.956876097 +0100
@@ -266,7 +266,10 @@ enum dma_status dma_sync_wait(struct dma
 			pr_err("%s: timeout!\n", __func__);
 			return DMA_ERROR;
 		}
-	} while (status == DMA_IN_PROGRESS);
+		if (status != DMA_IN_PROGRESS)
+			break;
+		cpu_relax();
+	} while (1);
 
 	return status;
 }
--
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