From 4631cd11e2904ae4a3eb58f54b9bd73a673b0c9d Mon Sep 17 00:00:00 2001
From: Niklas Cassel <niklas.cassel@axis.com>
Date: Mon, 26 Feb 2018 22:47:09 +0100
Subject: [PATCH 21/21] net: stmmac: make dwmac4_release_tx_desc() clear all
 descriptor fields
Git-commit: 1e88f6e01bc094c9fc7021cc1944d14a63257703
Patch-mainline: v4.17-rc1
References: git-fixes

Make dwmac4_release_tx_desc() clear all descriptor fields, not just
TDES2 and TDES3.

I'm suspecting that TDES0 and TDES1 wasn't cleared because the DMA
engine uses them to store the tx hardware timestamp (if PTP is enabled).

However, stmmac_tx_clean() calls stmmac_get_tx_hwtstamp(), which reads
and saves the timestamp, before it calls release_tx_desc(), so this
is not an issue.

stmmac_xmit() and stmmac_tso_xmit() both always overwrite TDES0,
however, stmmac_tso_xmit() sometimes sets TDES1, and since neither
stmmac_xmit() nor stmmac_tso_xmit() explicitly clears TDES1, both
functions might reuse a DMA descriptor with old TDES1 data.

I haven't observed any misbehavior even though TDES1 sometimes
point to an old skb, however, explicitly clearing both TDES0 and TDES1
in dwmac4_release_tx_desc() minimizes the chances of undefined behavior.

Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Denis Kirjanov <denis.kirjanov@suse.com>
---
 drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
index 37b77e7da132..5dd9f015407d 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
@@ -392,6 +392,8 @@ static void dwmac4_rd_prepare_tso_tx_desc(struct dma_desc *p, int is_fs,
 
 static void dwmac4_release_tx_desc(struct dma_desc *p, int mode)
 {
+	p->des0 = 0;
+	p->des1 = 0;
 	p->des2 = 0;
 	p->des3 = 0;
 }
-- 
2.16.4