[PATCH net-next v2 05/14] net: stmmac: add TSO check for header length

[Russell King (Oracle)]

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 at armlinux.org.uk>
---
 .../net/ethernet/stmicro/stmmac/stmmac_main.c   | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 2b5bccc727a5..031ffb78f40d 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -4385,6 +4385,20 @@ static size_t stmmac_tso_header_size(struct sk_buff *skb)
 	return size;
 }
 
+/* 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.
+ *
+ * While IPv4 is limited to MAC+VLAN+IPv4+ext+TCP+ext = 138 bytes, the IPv6
+ * extension headers aren't similarly limited.
+ */
+static bool stmmac_tso_valid_packet(struct sk_buff *skb)
+{
+	size_t header_len = stmmac_tso_header_size(skb);
+
+	return header_len <= 1023;
+}
+
 /**
  *  stmmac_tso_xmit - Tx entry point of the driver for oversized frames (TSO)
  *  @skb : the socket buffer
@@ -4945,7 +4959,8 @@ static netdev_features_t stmmac_features_check(struct sk_buff *skb,
 
 	if (skb_is_gso(skb)) {
 		queue = skb_get_queue_mapping(skb);
-		if (!stmmac_tso_channel_permitted(netdev_priv(dev), queue))
+		if (!stmmac_tso_channel_permitted(netdev_priv(dev), queue) ||
+		    !stmmac_tso_valid_packet(skb))
 			features &= ~NETIF_F_GSO_MASK;
 	}
 
-- 
2.47.3