netdev - [PATCH net-next v2 3/3] r8169: use WRITE_ONCE instead of dma_wmb in rtl8169_mark_to

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Message-ID: <612105ff-f21d-40c4-2b02-0ac0c12615fb@gmail.com>
Date:   Sun, 19 Apr 2020 20:16:21 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Realtek linux nic maintainers <nic_swsd@...ltek.com>,
        David Miller <davem@...emloft.net>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: [PATCH net-next v2 3/3] r8169: use WRITE_ONCE instead of dma_wmb in
 rtl8169_mark_to_asic

We want to ensure that desc->opts1 is written as last descriptor field.
This doesn't require a full compiler barrier, WRITE_ONCE provides the
ordering guarantee we need.

Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
---
 drivers/net/ethernet/realtek/r8169_main.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
index 2fc65aca3..3e4ed2528 100644
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -3892,11 +3892,9 @@ static inline void rtl8169_mark_to_asic(struct RxDesc *desc)
 {
 	u32 eor = le32_to_cpu(desc->opts1) & RingEnd;
 
-	desc->opts2 = 0;
-	/* Force memory writes to complete before releasing descriptor */
-	dma_wmb();
-
-	desc->opts1 = cpu_to_le32(DescOwn | eor | R8169_RX_BUF_SIZE);
+	/* Ensure ordering of writes */
+	WRITE_ONCE(desc->opts2, 0);
+	WRITE_ONCE(desc->opts1, cpu_to_le32(DescOwn | eor | R8169_RX_BUF_SIZE));
 }
 
 static struct page *rtl8169_alloc_rx_data(struct rtl8169_private *tp,
@@ -3919,7 +3917,7 @@ static struct page *rtl8169_alloc_rx_data(struct rtl8169_private *tp,
 		return NULL;
 	}
 
-	desc->addr = cpu_to_le64(mapping);
+	WRITE_ONCE(desc->addr, cpu_to_le64(mapping));
 	rtl8169_mark_to_asic(desc);
 
 	return data;
-- 
2.26.1