net: stmmac: dwmac4: stop hardware from dropping checksum-error packets

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/[email protected]/

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

Signed-off-by: Oleksij Rempel <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: olerem

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

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;