[PATCH v2 2/2] dma: mmp_pdma: clear DRCMR when free a phy channel

From: Xiang Wang
Date: Wed Jun 05 2013 - 22:25:43 EST

From: Xiang Wang <wangx@xxxxxxxxxxx>

In mmp pdma, phy channels are allocated/freed dynamically.
The mapping from DMA request to DMA channel number in DRCMR
should be cleared when a phy channel is freed. Otherwise
conflicts will happen when:
1. A is using channel 2 and free it after finished, but A
still maps to channel 2 in DRCMR of A.
2. Now another one B gets channel 2. So B maps to channel 2
too in DRCMR of B.
In the datasheet, it is described that "Do not map two active
requests to the same channel since it produces unpredictable
results" and we can observe that during test.

Signed-off-by: Xiang Wang <wangx@xxxxxxxxxxx>
drivers/dma/mmp_pdma.c | 6 ++++++
1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/dma/mmp_pdma.c b/drivers/dma/mmp_pdma.c
index 84e51a1..410dc26 100644
--- a/drivers/dma/mmp_pdma.c
+++ b/drivers/dma/mmp_pdma.c
@@ -252,10 +252,16 @@ static void free_phy(struct mmp_pdma_chan *pchan)
struct mmp_pdma_device *pdev = to_mmp_pdma_dev(pchan->chan.device);
unsigned long flags;
+ u32 reg;

if (!pchan->phy)

+ /* clear the channel mapping in DRCMR */
+ reg = pchan->phy->vchan->drcmr;
+ reg = ((reg < 64) ? 0x0100 : 0x1100) + ((reg & 0x3f) << 2);
+ writel(0, pchan->phy->base + reg);
spin_lock_irqsave(&pdev->phy_lock, flags);
pchan->phy->vchan = NULL;
pchan->phy = NULL;

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/