[PATCH net 2/3] net: stmmac: dwmac1000: don't discard frames with only a checksum error

[Grische <opensource@grische.xyz>]

On dwmac1000 with enhanced descriptors, the hardware sets the Error
Summary (ES) bit of the Rx descriptor not only for L2 errors but also
for an L3/L4 checksum error. enh_desc_get_rx_status() returns
discard_frame whenever ES is set, and since commit 1b746ce8b397 ("net:
stmmac: don't overwrite discard_frame status") the checksum status is
only evaluated for good frames.

Return discard_frame only for L2 errors. A frame with only a checksum
error is then reported as csum_none and reaches the stack as
CHECKSUM_NONE, so the stack verifies the checksum itself. This matches
dwmac4, whose Error Summary check does not include the checksum bits.

Also drop the per-frame pr_err in enh_desc_get_rx_status(). Once the MAC
delivers checksum-error frames, it can be triggered from the wire.

This prepares for setting DMA_CONTROL_DT, which makes the MAC deliver
checksum-error frames instead of dropping them in its Rx FIFO.

Fixes: 1b746ce8b397 ("net: stmmac: don't overwrite discard_frame status")
Cc: <stable@vger.kernel.org> # 6.6.x: ee0aace5f844: net: stmmac: Correctly handle Rx checksum offload errors
Cc: <stable@vger.kernel.org> # 6.6.x
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Grische <opensource@grische.xyz>
---
 drivers/net/ethernet/stmicro/stmmac/enh_desc.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/enh_desc.c b/drivers/net/ethernet/stmicro/stmmac/enh_desc.c
index 051253601225..5c43d32a2f22 100644
--- a/drivers/net/ethernet/stmicro/stmmac/enh_desc.c
+++ b/drivers/net/ethernet/stmicro/stmmac/enh_desc.c
@@ -195,9 +195,6 @@ static int enh_desc_get_rx_status(struct stmmac_extra_stats *x,
 		if (unlikely(rdes0 & RDES0_OVERFLOW_ERROR))
 			x->rx_gmac_overflow++;
 
-		if (unlikely(rdes0 & RDES0_IPC_CSUM_ERROR))
-			pr_err("\tIPC Csum Error/Giant frame\n");
-
 		if (unlikely(rdes0 & RDES0_COLLISION))
 			x->rx_collision++;
 		if (unlikely(rdes0 & RDES0_RECEIVE_WATCHDOG))
@@ -209,7 +206,11 @@ static int enh_desc_get_rx_status(struct stmmac_extra_stats *x,
 		if (unlikely(rdes0 & RDES0_CRC_ERROR)) {
 			x->rx_crc_errors++;
 		}
-		ret = discard_frame;
+		if (rdes0 & (RDES0_DESCRIPTOR_ERROR | RDES0_OVERFLOW_ERROR |
+			     RDES0_COLLISION | RDES0_RECEIVE_WATCHDOG |
+			     RDES0_MII_ERROR | RDES0_CRC_ERROR |
+			     RDES0_LENGTH_ERROR))
+			ret = discard_frame;
 	}
 
 	/* After a payload csum error, the ES bit is set.
-- 
2.54.0