[PATCH net-next 02/10] net: stmmac: add TSO check for header length

["Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>]

According to the STM32MP151 documentation which covers dwmac v4.2, the
hardware TSO feature can handle header lengths up to a maximum of 1023
bytes.

Add a .ndo_features_check() method implementation to check the header
length meets these requirements, otherwise fall back to software GSO.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 2957ee4a43db..e21ca1c70c6d 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -4940,6 +4940,14 @@ static netdev_features_t stmmac_features_check(struct sk_buff *skb,
 		queue = skb_get_queue_mapping(skb);
 		if (!stmmac_channel_tso_permitted(netdev_priv(dev), queue))
 			features &= ~NETIF_F_GSO_MASK;
+
+		/* STM32MP151 (dwmac v4.2) and STM32MP25xx (dwmac v5.3) states
+		 * for TDES2 normal (read format) descriptor that the maximum
+		 * header length supported for the TSO feature is 1023 bytes.
+		 * Fall back to software GSO for these skbs.
+		 */
+		if (skb_headlen(skb) > 1023)
+			features &= ~NETIF_F_GSO_MASK;
 	}
 
 	return features;
-- 
2.47.3