[PATCH 4.16 225/272] net: stmmac: ensure that the device has released ownership before reading data

[Greg Kroah-Hartman]

4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Niklas Cassel <niklas.cassel@xxxxxxxx>

[ Upstream commit a6b25da5e7ba212af5826a662e6a035a79bffabd ]

According to Documentation/memory-barriers.txt, we need to use a
dma_rmb() after reading the status/own bit, to ensure that all
descriptor fields are read after reading the own bit.

This way, we ensure that the DMA engine is done with the DMA
descriptor before we read the other descriptor fields, e.g. reading
the tx hardware timestamp (if PTP is enabled).

Signed-off-by: Niklas Cassel <niklas.cassel@xxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -1843,6 +1843,11 @@ static void stmmac_tx_clean(struct stmma
 		if (unlikely(status & tx_dma_own))
 			break;
 
+		/* Make sure descriptor fields are read after reading
+		 * the own bit.
+		 */
+		dma_rmb();
+
 		/* Just consider the last segment and ...*/
 		if (likely(!(status & tx_not_ls))) {
 			/* ... verify the status error condition */