[PATCH 4.9 26/76] dmaengine: at_hdmac: Dont allow CPU to reorder channel enable

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From: Tudor Ambarus <tudor.ambarus@xxxxxxxxxxxxx>

commit 580ee84405c27d6ed419abe4d2b3de1968abdafd upstream.

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>
Signed-off-by: Tudor Ambarus <tudor.ambarus@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/lkml/13c6c9a2-6db5-c3bf-349b-4c127ad3496a@xxxxxxxxxx/
Acked-by: Nicolas Ferre <nicolas.ferre@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20221025090306.297886-1-tudor.ambarus@xxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20221025090306.297886-14-tudor.ambarus@xxxxxxxxxxxxx
Signed-off-by: Vinod Koul <vkoul@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/dma/at_hdmac.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/dma/at_hdmac.c
+++ b/drivers/dma/at_hdmac.c
@@ -253,6 +253,8 @@ static void atc_dostart(struct at_dma_ch
 		       ATC_SPIP_BOUNDARY(first->boundary));
 	channel_writel(atchan, DPIP, ATC_DPIP_HOLE(first->dst_hole) |
 		       ATC_DPIP_BOUNDARY(first->boundary));
+	/* Don't allow CPU to reorder channel enable. */
+	wmb();
 	dma_writel(atdma, CHER, atchan->mask);
 
 	vdbg_dump_regs(atchan);





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