[PATCH 6/6] net: dwc_eth_qos: Prevent DMA from writing updated RX DMA descriptor

Marek Vasut marex at denx.de
Mon Mar 23 02:45:26 CET 2020

The DMA may attempt to write a DMA descriptor in the ring while it is
being updated. By writing the DMA descriptor buffer address to 0, it
is assured the DMA will not use such a buffer and the buffer can be
updated without any interference.

Signed-off-by: Marek Vasut <marex at denx.de>
Cc: Joe Hershberger <joe.hershberger at ni.com>
Cc: Patrice Chotard <patrice.chotard at st.com>
Cc: Patrick Delaunay <patrick.delaunay at st.com>
Cc: Ramon Fried <rfried.dev at gmail.com>
Cc: Stephen Warren <swarren at nvidia.com>
 drivers/net/dwc_eth_qos.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/dwc_eth_qos.c b/drivers/net/dwc_eth_qos.c
index 7dadb10fe7..c86b9d59a5 100644
--- a/drivers/net/dwc_eth_qos.c
+++ b/drivers/net/dwc_eth_qos.c
@@ -1431,8 +1431,10 @@ static int eqos_free_pkt(struct udevice *dev, uchar *packet, int length)
 	rx_desc = &(eqos->rx_descs[eqos->rx_desc_idx]);
+	rx_desc->des0 = 0;
+	mb();
+	eqos->config->ops->eqos_flush_desc(rx_desc);
 	eqos->config->ops->eqos_inval_buffer(packet, length);
 	rx_desc->des0 = (u32)(ulong)packet;
 	rx_desc->des1 = 0;
 	rx_desc->des2 = 0;

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