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realtek: eth: cleanup packet length calculation

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During transmit the driver must adapt the packet length. The
hardware requires at least a memory space of ETH_ZLEN bytes
data plus four bytes for layer 2 FCS. This was calculated
(somehow) but skb->len never got updated and for the minimum
length a RTL838x specific workaround was in place. Clean up
the code and use skb_put_padto() so the length change gets
reflected in skb->len.

While we are here drop zeroing DSA tag because it will be
overwritten by hardware for FCS.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/21999
Signed-off-by: Robert Marko <robimarko@gmail.com>
This commit is contained in:
Markus Stockhausen 2026-02-12 14:53:11 +01:00 • committed by Robert Marko
parent a36ab12454
commit 47d0773d7d
1 changed files with 7 additions and 13 deletions
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20
target/linux/realtek/files-6.12/drivers/net/ethernet/rtl838x_eth.c
View file

@ -8,6 +8,7 @@
#include <linux/etherdevice.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/minmax.h>
#include <linux/platform_device.h>
#include <linux/sched.h>
#include <linux/slab.h>
@ -977,16 +978,15 @@ static int rteth_start_xmit(struct sk_buff *skb, struct net_device *netdev)
skb->data[len - 3] < ctrl->r->cpu_port &&
skb->data[len - 2] == 0x10 &&
skb->data[len - 1] == 0x00) {
/* DSA tag, reuse space for CRC */
dest_port = skb->data[len - 3];
skb->data[len - 4] = skb->data[len - 3] = 0;
skb->data[len - 2] = skb->data[len - 1] = 0;
/* space will be reused for 4 byte layer 2 FCS */
} else {
/* No DSA tag, add space for CRC */
len += 4;
/* No DSA tag, add space for 4 byte layer 2 FCS */
len += ETH_FCS_LEN;
}
if (unlikely(skb_padto(skb, len))) {
len = max(ETH_ZLEN + ETH_FCS_LEN, len);
if (unlikely(skb_put_padto(skb, len))) {
netdev->stats.tx_errors++;
dev_warn(dev, "skb pad failed\n");
@ -1005,7 +1005,7 @@ static int rteth_start_xmit(struct sk_buff *skb, struct net_device *netdev)
return NETDEV_TX_BUSY;
}
packet->dma = dma_map_single(dev, skb->data, skb->len, DMA_TO_DEVICE);
packet->dma = dma_map_single(dev, skb->data, len, DMA_TO_DEVICE);
if (unlikely(dma_mapping_error(dev, packet->dma))) {
dev_kfree_skb_any(skb);
netdev->stats.tx_errors++;
@ -1019,12 +1019,6 @@ static int rteth_start_xmit(struct sk_buff *skb, struct net_device *netdev)
dev_kfree_skb_any(packet->skb);
}
if (ctrl->r->family_id == RTL8380_FAMILY_ID) {
/* On RTL8380 SoCs, small packet lengths being sent need adjustments */
if (len < ETH_ZLEN - 4)
len -= 4;
}
if (dest_port >= 0)
ctrl->r->create_tx_header(packet, dest_port, 0); // TODO ok to set prio to 0?