dmaengine: fix interrupt clearing for mv_xor

When using simultaneously the two DMA channels on a same engine, some
transfers are never completed. For example, an endless lock can occur
while writing heavily on a RAID5 array (with async-tx offload support
enabled).

Note that this issue can also be reproduced by using the DMA test
client.

On a same engine, the interrupt cause register is shared between two
DMA channels. This patch make sure that the cause bit is only cleared
for the requested channel.
Signed-off-by: Simon Guinot <sguinot@lacie.com>
Tested-by: Luc Saillard <luc@saillard.org>
Acked-by: saeed bishara <saeed.bishara@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/dma/mv_xor.c

@@ -162,7 +162,7 @@ static int mv_is_err_intr(u32 intr_cause)
 
 static void mv_xor_device_clear_eoc_cause(struct mv_xor_chan *chan)
 {
-	u32 val = (1 << (1 + (chan->idx * 16)));
+	u32 val = ~(1 << (chan->idx * 16));
 	dev_dbg(chan->device->common.dev, "%s, val 0x%08x\n", __func__, val);
 	__raw_writel(val, XOR_INTR_CAUSE(chan));
 }