[PATCH 19/33] dmaengine: at_hdmac: Don't allow CPU to reorder channel enable

[Tudor Ambarus]

at_hdmac uses __raw_writel for register writes. In the absence of a
barrier, the CPU may reorder the register operations.
Introduce a write memory barrier so that the CPU does not reorder the
channel enable, thus the start of the transfer, without making sure that
all the pre-required register fields are already written.

Fixes: dc78baa2b90b ("dmaengine: at_hdmac: new driver for the Atmel AHB DMA Controller")
Reported-by: Peter Rosin <peda@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Tudor Ambarus <tudor.ambarus@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/13c6c9a2-6db5-c3bf-349b-4c127ad3496a@xxxxxxxxxx/
---
 drivers/dma/at_hdmac.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/dma/at_hdmac.c b/drivers/dma/at_hdmac.c
index 825a29ede35e..1cb0d26d30ed 100644
--- a/drivers/dma/at_hdmac.c
+++ b/drivers/dma/at_hdmac.c
@@ -691,6 +691,8 @@ static void atc_dostart(struct at_dma_chan *atchan, struct at_desc *first)
 	channel_writel(atchan, DPIP, FIELD_PREP(ATC_DPIP_HOLE,
 						first->dst_hole) |
 		       FIELD_PREP(ATC_DPIP_BOUNDARY, first->boundary));
+	/* Don't allow CPU to reorder channel enable. */
+	wmb();
 	dma_writel(atdma, CHER, atchan->mask);
 
 	vdbg_dump_regs(atchan);
-- 
2.25.1