[openwrt/openwrt] realtek: Fix buffer length calculation on RTL8380 with CRC offload

[LEDE Commits]

hauke pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/76428494c323d0bb6572f9a2d247092b322fa221

commit 76428494c323d0bb6572f9a2d247092b322fa221
Author: Birger Koblitz <mail at birger-koblitz.de>
AuthorDate: Sun Jun 6 16:20:59 2021 +0200

    realtek: Fix buffer length calculation on RTL8380 with CRC offload
    
    Fixes the buffer and packet length calculations for Ethernet TX on
    the RTL8380 SoC when CRC calculation offload is enabled.
    CRC-offload is always done by the SoC, but additional CRC
    calculation was previously done also by the kernel.
    It also fixes detection of the DSA tag for packets on RTL8390
    SoCs for ports > 28.
    
    v2 has correct whitespace
    
    Signed-off-by: Birger Koblitz <mail at birger-koblitz.de>
---
 .../realtek/files-5.4/drivers/net/ethernet/rtl838x_eth.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/target/linux/realtek/files-5.4/drivers/net/ethernet/rtl838x_eth.c b/target/linux/realtek/files-5.4/drivers/net/ethernet/rtl838x_eth.c
index c5c6e3b6b7..de54868cad 100644
--- a/target/linux/realtek/files-5.4/drivers/net/ethernet/rtl838x_eth.c
+++ b/target/linux/realtek/files-5.4/drivers/net/ethernet/rtl838x_eth.c
@@ -1129,23 +1129,16 @@ static int rtl838x_eth_tx(struct sk_buff *skb, struct net_device *dev)
 
 	/* Check for DSA tagging at the end of the buffer */
 	if (netdev_uses_dsa(dev) && skb->data[len-4] == 0x80 && skb->data[len-3] > 0
-			&& skb->data[len-3] < 28 &&  skb->data[len-2] == 0x10
+			&& skb->data[len-3] < priv->cpu_port &&  skb->data[len-2] == 0x10
 			&&  skb->data[len-1] == 0x00) {
 		/* Reuse tag space for CRC if possible */
 		dest_port = skb->data[len-3];
+		skb->data[len-4] = skb->data[len-3] = skb->data[len-2] = skb->data[len-1] = 0x00;
 		len -= 4;
 	}
 
 	len += 4; // Add space for CRC
 
-	// On RTL8380 SoCs, the packet needs extra padding
-	if (priv->family_id == RTL8380_FAMILY_ID) {
-		if (len < ETH_ZLEN)
-			len = ETH_ZLEN; // SoC not automatically padding to ETH_ZLEN
-		else
-			len += 4;
-	}
-
 	if (skb_padto(skb, len)) {
 		ret = NETDEV_TX_OK;
 		goto txdone;
@@ -1158,6 +1151,11 @@ static int rtl838x_eth_tx(struct sk_buff *skb, struct net_device *dev)
 		h = &ring->tx_header[q][ring->c_tx[q]];
 		h->size = len;
 		h->len = len;
+		// On RTL8380 SoCs, small packet lengths being sent need adjustments
+		if (priv->family_id == RTL8380_FAMILY_ID) {
+			if (len < ETH_ZLEN - 4)
+				h->len -= 4;
+		}
 
 		priv->r->create_tx_header(h, dest_port, skb->priority >> 1);