net: stmmac: ensure that the device has released ownership before reading data

[ 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@axis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index d0cc737950560fe644d901a1ea67e4bfd3f2482a..40ae1be372ccb148b50a53a578b75227235d07ca 100644 (file)
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -1829,6 +1829,11 @@ static void stmmac_tx_clean(struct stmmac_priv *priv, u32 queue)
                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 */