[PATCH net-next v1 0/3] stmmac: stop silently dropping bad checksum packets

[PATCH net-next v1 0/3] stmmac: stop silently dropping bad checksum packets

[Oleksij Rempel]

Hi all,

this series reworks how stmmac handles receive checksum offload
(CoE) errors on dwmac4.

At present, when CoE is enabled, the hardware silently discards any
frame that fails checksum validation. These packets never reach the
driver and are not accounted in the generic drop statistics. They are
only visible in the stmmac-specific counters as "payload error" or
"header error" packets, which makes it harder to debug or monitor
network issues.

Following discussion [1], the driver is reworked to propagate checksum
error information up to the stack. With these changes, CoE stays
enabled, but frames that fail hardware validation are no longer dropped
in hardware. Instead, the driver marks them with CHECKSUM_NONE so the
network stack can validate, drop, and properly account them in the
standard drop statistics.

[1] https://lore.kernel.org/all/20250625132117.1b3264e8@kernel.org/

Oleksij Rempel (3):
  net: stmmac: Correctly handle Rx checksum offload errors
  net: stmmac: dwmac4: report Rx checksum errors in status
  net: stmmac: dwmac4: stop hardware from dropping checksum-error
    packets

 drivers/net/ethernet/stmicro/stmmac/dwmac4.h       | 1 +
 drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c | 8 ++++++--
 drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c   | 2 ++
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c  | 3 ++-
 4 files changed, 11 insertions(+), 3 deletions(-)

--
2.39.5

[PATCH net-next v1 1/3] net: stmmac: Correctly handle Rx checksum offload errors

[Oleksij Rempel]

The stmmac_rx function would previously set skb->ip_summed to
CHECKSUM_UNNECESSARY if hardware checksum offload (CoE) was enabled
and the packet was of a known IP ethertype.

However, this logic failed to check if the hardware had actually
reported a checksum error. The hardware status, indicating a header or
payload checksum failure, was being ignored at this stage. This could
cause corrupt packets to be passed up the network stack as valid.

This patch corrects the logic by checking the `csum_none` status flag,
which is set when the hardware reports a checksum error. If this flag
is set, skb->ip_summed is now correctly set to CHECKSUM_NONE,
ensuring the kernel's network stack will perform its own validation and
properly handle the corrupt packet.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 9a77390b7f9d..75d8d8042316 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -5733,7 +5733,8 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 
 		skb->protocol = eth_type_trans(skb, priv->dev);
 
-		if (unlikely(!coe) || !stmmac_has_ip_ethertype(skb))
+		if (unlikely(!coe) || !stmmac_has_ip_ethertype(skb) ||
+		    (status & csum_none))
 			skb_checksum_none_assert(skb);
 		else
 			skb->ip_summed = CHECKSUM_UNNECESSARY;
-- 
2.39.5

[PATCH net-next v1 2/3] net: stmmac: dwmac4: report Rx checksum errors in status

[Oleksij Rempel]

Propagate hardware checksum failures from the descriptor parser to the
caller.

Currently, dwmac4_wrback_get_rx_status() updates stats when the Rx
descriptor signals an IP header or payload checksum error, but it does
not reflect this in its return value. The higher-level stmmac_rx() code
therefore cannot tell that hardware checksum validation failed.

Set the csum_none flag in the returned status when either
RDES1_IP_HDR_ERROR or RDES1_IP_PAYLOAD_ERROR is present. This aligns
dwmac4 with enh_desc_coe_rdes0() and lets stmmac_rx() mark the skb as
CHECKSUM_NONE for software verification.

This is a preparatory step for disabling the hardware filter that drops
frames which do not pass checksum validation.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
index a5fb31eb0192..aac68dc28dc1 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_descs.c
@@ -110,16 +110,20 @@ static int dwmac4_wrback_get_rx_status(struct stmmac_extra_stats *x,
 
 	message_type = (rdes1 & ERDES4_MSG_TYPE_MASK) >> 8;
 
-	if (rdes1 & RDES1_IP_HDR_ERROR)
+	if (rdes1 & RDES1_IP_HDR_ERROR) {
 		x->ip_hdr_err++;
+		ret |= csum_none;
+	}
 	if (rdes1 & RDES1_IP_CSUM_BYPASSED)
 		x->ip_csum_bypassed++;
 	if (rdes1 & RDES1_IPV4_HEADER)
 		x->ipv4_pkt_rcvd++;
 	if (rdes1 & RDES1_IPV6_HEADER)
 		x->ipv6_pkt_rcvd++;
-	if (rdes1 & RDES1_IP_PAYLOAD_ERROR)
+	if (rdes1 & RDES1_IP_PAYLOAD_ERROR) {
 		x->ip_payload_err++;
+		ret |= csum_none;
+	}
 
 	if (message_type == RDES_EXT_NO_PTP)
 		x->no_ptp_rx_msg_type_ext++;
-- 
2.39.5

[PATCH net-next v1 3/3] net: stmmac: dwmac4: stop hardware from dropping checksum-error packets

[Oleksij Rempel]

Tell the MAC not to discard frames that fail TCP/IP checksum
validation.

By default, when the hardware checksum engine (CoE) is enabled,
dwmac4 silently drops any packet where the offload engine detects
a checksum error. These frames are not reported to the driver and
are not counted in any statistics as dropped packets.

Set the MTL_OP_MODE_DIS_TCP_EF bit when initializing the Rx channel so
that all packets are delivered, even if they failed hardware checksum
validation. CoE remains enabled, but instead of dropping such frames,
the driver propagates the error status and marks the skb with
CHECKSUM_NONE. This allows the stack to verify and drop the packet
while updating statistics.

This change follows the decision made in the discussion:
Link: https://lore.kernel.org/all/20250625132117.1b3264e8@kernel.org/

It depends on the previous patches that added proper error propagation
in the Rx path.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 drivers/net/ethernet/stmicro/stmmac/dwmac4.h     | 1 +
 drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4.h b/drivers/net/ethernet/stmicro/stmmac/dwmac4.h
index f4694fd576f5..3dec1a264cf6 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac4.h
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4.h
@@ -341,6 +341,7 @@ static inline u32 mtl_chanx_base_addr(const struct dwmac4_addrs *addrs,
 #define MTL_OP_MODE_RFA_SHIFT		8
 
 #define MTL_OP_MODE_EHFC		BIT(7)
+#define MTL_OP_MODE_DIS_TCP_EF		BIT(6)
 
 #define MTL_OP_MODE_RTC_MASK		GENMASK(1, 0)
 #define MTL_OP_MODE_RTC_SHIFT		0
diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
index 0cb84a0041a4..d87a8b595e6a 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
@@ -268,6 +268,8 @@ static void dwmac4_dma_rx_chan_op_mode(struct stmmac_priv *priv,
 
 	mtl_rx_op = readl(ioaddr + MTL_CHAN_RX_OP_MODE(dwmac4_addrs, channel));
 
+	mtl_rx_op |= MTL_OP_MODE_DIS_TCP_EF;
+
 	if (mode == SF_DMA_MODE) {
 		pr_debug("GMAC: enable RX store and forward mode\n");
 		mtl_rx_op |= MTL_OP_MODE_RSF;
-- 
2.39.5

Re: [PATCH net-next v1 0/3] stmmac: stop silently dropping bad checksum packets

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon, 18 Aug 2025 11:02:14 +0200 you wrote:
> Hi all,
> 
> this series reworks how stmmac handles receive checksum offload
> (CoE) errors on dwmac4.
> 
> At present, when CoE is enabled, the hardware silently discards any
> frame that fails checksum validation. These packets never reach the
> driver and are not accounted in the generic drop statistics. They are
> only visible in the stmmac-specific counters as "payload error" or
> "header error" packets, which makes it harder to debug or monitor
> network issues.
> 
> [...]

Here is the summary with links:
  - [net-next,v1,1/3] net: stmmac: Correctly handle Rx checksum offload errors
    https://git.kernel.org/netdev/net-next/c/ee0aace5f844
  - [net-next,v1,2/3] net: stmmac: dwmac4: report Rx checksum errors in status
    https://git.kernel.org/netdev/net-next/c/644b8437ccef
  - [net-next,v1,3/3] net: stmmac: dwmac4: stop hardware from dropping checksum-error packets
    https://git.kernel.org/netdev/net-next/c/fe4042797651

You are awesome, thank you!
-- 
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Re: [PATCH net-next v1 0/3] stmmac: stop silently dropping bad checksum packets

[Russell King (Oracle)]

On Mon, Aug 18, 2025 at 11:02:14AM +0200, Oleksij Rempel wrote:
> Hi all,
> 
> this series reworks how stmmac handles receive checksum offload
> (CoE) errors on dwmac4.
> 
> At present, when CoE is enabled, the hardware silently discards any
> frame that fails checksum validation. These packets never reach the
> driver and are not accounted in the generic drop statistics. They are
> only visible in the stmmac-specific counters as "payload error" or
> "header error" packets, which makes it harder to debug or monitor
> network issues.

FYI, there are counters at 0x214 and 0x228 that indicate header
problems, including checksum failures. There are also counters
at 0x234, 0x23c, 0x244 that count udp, tcp and icmp checksum
errors.

So, the hardware does keep statistics. Maybe we should make use
of those rather than the approach in this series?

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