[PATCH] dmaengine: mv_xor: add missing dma_wmb() barriers before descriptor chain start

[Rosen Penev <rosenp@gmail.com>]

The descriptor data written to coherent memory must be visible to the
DMA engine before the HW registers that trigger processing are written.

Add a dma_wmb() before mv_chan_set_next_descriptor() in
mv_chan_start_new_chain() to order descriptor fields before the
descriptor-pointer write.

Add a dma_wmb() after mv_desc_set_next_desc() in
mv_chan_handle_chain_append() to order the chain link write before
the subsequent check of the current-descriptor register. Without the
barrier the hardware may observe stale descriptor data.

Fixes: ff7b04796d98 ("DMA engine driver for Marvell XOR engine")
Assisted-by: opencode:big-pickle
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 drivers/dma/mv_xor.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/dma/mv_xor.c b/drivers/dma/mv_xor.c
index 24f22db5dfa1..6db7dafac9c8 100644
--- a/drivers/dma/mv_xor.c
+++ b/drivers/dma/mv_xor.c
@@ -181,6 +181,7 @@ static void mv_chan_start_new_chain(struct mv_xor_chan *mv_chan,
 	dev_dbg(mv_chan_to_devp(mv_chan), "%s %d: sw_desc %p\n",
 		__func__, __LINE__, sw_desc);
 
+	dma_wmb();
 	/* set the hardware chain */
 	mv_chan_set_next_descriptor(mv_chan, sw_desc->async_tx.phys);
 
@@ -409,6 +410,7 @@ mv_xor_tx_submit(struct dma_async_tx_descriptor *tx)
 
 		/* fix up the hardware chain */
 		mv_desc_set_next_desc(old_chain_tail, sw_desc->async_tx.phys);
+		dma_wmb();
 
 		/* if the channel is not busy */
 		if (!mv_chan_is_busy(mv_chan)) {
-- 
2.55.0