[PATCH net-next 2/7] net: bcmgenet: allow a continuation descriptor without the alignment pad

[Nicolai Buchwitz]

A frame longer than the packet ready threshold arrives in several
descriptors, each with its own status block. Only the first one also
carries the two alignment bytes. The length check assumes the pad is always
there, so a continuation holding a single byte looks two bytes too short
and the whole frame is dropped.

Account for the pad on the first descriptor only.

The MTU cannot produce a frame past the threshold yet, so nothing hits this
today. It is preparation for the larger MTU.

Signed-off-by: Nicolai Buchwitz <nb@xxxxxxxxxxx>
Tested-by: Pierre-Marin Leclercq <pierremarinleclercq88@xxxxxxxxx>
---
 drivers/net/ethernet/broadcom/genet/bcmgenet.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
index a82579879f4b..d89ae6599760 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
@@ -2329,6 +2329,7 @@ static unsigned int bcmgenet_desc_rx(struct bcmgenet_rx_ring *ring,
 		unsigned int rx_offset, rx_size;
 		struct status_64 *status;
 		struct page *rx_page;
+		unsigned int min_len;
 		void *hard_start;
 		__be16 rx_csum;
 
@@ -2365,8 +2366,12 @@ static unsigned int bcmgenet_desc_rx(struct bcmgenet_rx_ring *ring,
 			  __func__, p_index, ring->c_index,
 			  ring->read_ptr, dma_length_status);
 
+		/* Only the first descriptor carries the alignment pad */
+		min_len = dma_flag & DMA_SOP ? GENET_RSB_PAD
+					     : sizeof(struct status_64);
+
 		/* Reject lengths that would underflow the SKB build path. */
-		if (unlikely(len > RX_BUF_LENGTH || len < GENET_RSB_PAD)) {
+		if (unlikely(len > RX_BUF_LENGTH || len < min_len)) {
 			netif_err(priv, rx_status, dev,
 				  "invalid packet length %d\n", len);
 			BCMGENET_STATS64_INC(stats, length_errors);

-- 
2.53.0