[PATCH v2] gemini: Backport upstream TSO disable patch

[Linus Walleij]

This patch is needed for ethernet to work on most Gemini
devices so backport it.

Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
---
Changes in v2:
- Also send the patch to openwrt-devel :/
- Link to v1: https://lore.kernel.org/r/20240123-gemini-ethernet-fix-v1-1-0bbe0b272962@linaro.org
---
 ...6.8-net-ethernet-cortina-Drop-TSO-support.patch | 78 ++++++++++++++++++++++
 1 file changed, 78 insertions(+)

diff --git a/target/linux/gemini/patches-6.1/0030-v6.8-net-ethernet-cortina-Drop-TSO-support.patch b/target/linux/gemini/patches-6.1/0030-v6.8-net-ethernet-cortina-Drop-TSO-support.patch
new file mode 100644
index 000000000000..41364804f845
--- /dev/null
+++ b/target/linux/gemini/patches-6.1/0030-v6.8-net-ethernet-cortina-Drop-TSO-support.patch
@@ -0,0 +1,78 @@
+From ac631873c9e7a50d2a8de457cfc4b9f86666403e Mon Sep 17 00:00:00 2001
+From: Linus Walleij <linus.walleij at linaro.org>
+Date: Sat, 6 Jan 2024 01:12:22 +0100
+Subject: [PATCH] net: ethernet: cortina: Drop TSO support
+
+The recent change to allow large frames without hardware checksumming
+slotted in software checksumming in the driver if hardware could not
+do it.
+
+This will however upset TSO (TCP Segment Offloading). Typical
+error dumps includes this:
+
+skb len=2961 headroom=222 headlen=66 tailroom=0
+(...)
+WARNING: CPU: 0 PID: 956 at net/core/dev.c:3259 skb_warn_bad_offload+0x7c/0x108
+gemini-ethernet-port: caps=(0x0000010000154813, 0x00002007ffdd7889)
+
+And the packets do not go through.
+
+The TSO implementation is bogus: a TSO enabled driver must propagate
+the skb_shinfo(skb)->gso_size value to the TSO engine on the NIC.
+
+Drop the size check and TSO offloading features for now: this
+needs to be fixed up properly.
+
+After this ethernet works fine on Gemini devices with a direct connected
+PHY such as D-Link DNS-313.
+
+Also tested to still be working with a DSA switch using the Gemini
+ethernet as conduit interface.
+
+Link: https://lore.kernel.org/netdev/CANn89iJLfxng1sYL5Zk0mknXpyYQPCp83m3KgD2KJ2_hKCpEUg@mail.gmail.com/
+Suggested-by: Eric Dumazet <edumazet at google.com>
+Fixes: d4d0c5b4d279 ("net: ethernet: cortina: Handle large frames")
+Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
+Reviewed-by: Eric Dumazet <edumazet at google.com>
+Signed-off-by: David S. Miller <davem at davemloft.net>
+---
+ drivers/net/ethernet/cortina/gemini.c | 15 ++-------------
+ 1 file changed, 2 insertions(+), 13 deletions(-)
+
+--- a/drivers/net/ethernet/cortina/gemini.c
++++ b/drivers/net/ethernet/cortina/gemini.c
+@@ -79,8 +79,7 @@ MODULE_PARM_DESC(debug, "Debug level (0=
+ #define GMAC0_IRQ4_8 (GMAC0_MIB_INT_BIT | GMAC0_RX_OVERRUN_INT_BIT)
+ 
+ #define GMAC_OFFLOAD_FEATURES (NETIF_F_SG | NETIF_F_IP_CSUM | \
+-		NETIF_F_IPV6_CSUM | NETIF_F_RXCSUM | \
+-		NETIF_F_TSO | NETIF_F_TSO_ECN | NETIF_F_TSO6)
++			       NETIF_F_IPV6_CSUM | NETIF_F_RXCSUM)
+ 
+ /**
+  * struct gmac_queue_page - page buffer per-page info
+@@ -1143,23 +1142,13 @@ static int gmac_map_tx_bufs(struct net_d
+ 	struct gmac_txdesc *txd;
+ 	skb_frag_t *skb_frag;
+ 	dma_addr_t mapping;
+-	unsigned short mtu;
+ 	void *buffer;
+ 	int ret;
+ 
+-	mtu  = ETH_HLEN;
+-	mtu += netdev->mtu;
+-	if (skb->protocol == htons(ETH_P_8021Q))
+-		mtu += VLAN_HLEN;
+-
++	/* TODO: implement proper TSO using MTU in word3 */
+ 	word1 = skb->len;
+ 	word3 = SOF_BIT;
+ 
+-	if (word1 > mtu) {
+-		word1 |= TSS_MTU_ENABLE_BIT;
+-		word3 |= mtu;
+-	}
+-
+ 	if (skb->len >= ETH_FRAME_LEN) {
+ 		/* Hardware offloaded checksumming isn't working on frames
+ 		 * bigger than 1514 bytes. A hypothesis about this is that the

---
base-commit: 65fb97b4507bcff3f98739975e9cc7df53137b12
change-id: 20240123-gemini-ethernet-fix-d161681eeb45

Best regards,
-- 
Linus Walleij <linus.walleij at linaro.org>