[PATCH 4/6] dmaengine: plx_dma: add dma_rmb() after observing write-back status

[Logan Gunthorpe <logang@deltatee.com>]

Add a dma_rmb() after the write-back status check so reads of the
transferred data can't be satisfied before the read that showed the
transfer was complete.

Reported-by: Sashiko <sashiko-bot@kernel.org>
Link: https://lore.kernel.org/dmaengine/20260717223217.B6FBF1F000E9@smtp.kernel.org
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 drivers/dma/plx_dma.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/dma/plx_dma.c b/drivers/dma/plx_dma.c
index 1c995f0c4463..e4243b66f933 100644
--- a/drivers/dma/plx_dma.c
+++ b/drivers/dma/plx_dma.c
@@ -148,6 +148,12 @@ static void plx_dma_process_desc(struct plx_dma_dev *plxdev)
 		if (flags & PLX_DESC_FLAG_VALID)
 			break;
 
+		/*
+		 * Ensure the write-back status is read before the
+		 * completed transfer's payload.
+		 */
+		dma_rmb();
+
 		res.residue = desc->orig_size - (flags & PLX_DESC_SIZE_MASK);
 
 		if (flags & PLX_DESC_WB_SUCCESS)
-- 
2.47.3