realtek: eth: cleanup packet length calculation

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>

diff --git a/target/linux/realtek/files-6.12/drivers/net/ethernet/rtl838x_eth.c b/target/linux/realtek/files-6.12/drivers/net/ethernet/rtl838x_eth.c
index 7a557afb64d210509c3d17950f7ba8d508b0c005..65843f822d803bc5b079f43fef48c11fd79cfde5 100644 (file)
--- a/target/linux/realtek/files-6.12/drivers/net/ethernet/rtl838x_eth.c
+++ b/target/linux/realtek/files-6.12/drivers/net/ethernet/rtl838x_eth.c
@@ -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?