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net: macb: exclude software FCS from TX byte statistics

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Frames for which macb_pad_and_fcs() supplies the FCS have four FCS
bytes appended, and TX completion then accounts the grown skb->len.
tx_bytes is defined to exclude the FCS, so these frames are reported
four bytes too large.

Track only the number of FCS bytes appended in software, 0 or
ETH_FCS_LEN, and subtract that from skb->len at completion. skb->len
already reflects the padded length by then, so there is nothing else
to store. macb_pad_and_fcs() already returns 0 on every non-error
path. Return the FCS length from there instead, rather than
recomputing the same check in the caller. BQL stays on the padded
skb->len that netdev_tx_sent_queue() saw.

Fixes: 653e92a917 ("net: macb: add support for padding and fcs computation")
Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>
Link: https://patch.msgid.link/20260831113128.1678674-1-nb@tipi-net.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Nicolai Buchwitz 2026-08-31 13:31:28 +02:00 committed by Jakub Kicinski
parent debac3a20d
commit d85f521a9a
2 changed files with 16 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
drivers/net/ethernet/cadence/macb.h
View File

@ -968,6 +968,8 @@ struct macb_dma_desc_ptp {
* of the frame
* @mapping: DMA address of the skb's fragment buffer
* @size: size of the DMA mapped buffer
* @fcs_len: FCS bytes appended in software, 0 or ETH_FCS_LEN, only
* set for the last buffer of the frame
* @mapped_as_page: true when buffer was mapped with skb_frag_dma_map(),
* false when buffer was mapped with dma_map_single()
*/
@ -975,6 +977,7 @@ struct macb_tx_skb {
struct sk_buff *skb;
dma_addr_t mapping;
size_t size;
u8 fcs_len;
bool mapped_as_page;
};

21
drivers/net/ethernet/cadence/macb_main.c
View File

@ -1322,8 +1322,8 @@ static void macb_tx_error_task(struct work_struct *work)
bp->netdev->stats.tx_packets++;
queue->stats.tx_packets++;
packets++;
bp->netdev->stats.tx_bytes += skb->len;
queue->stats.tx_bytes += skb->len;
bp->netdev->stats.tx_bytes += skb->len - tx_skb->fcs_len;
queue->stats.tx_bytes += skb->len - tx_skb->fcs_len;
bytes += skb->len;
}
} else {
@ -1450,8 +1450,8 @@ static int macb_tx_complete(struct macb_queue *queue, int budget)
skb->data);
bp->netdev->stats.tx_packets++;
queue->stats.tx_packets++;
bp->netdev->stats.tx_bytes += skb->len;
queue->stats.tx_bytes += skb->len;
bp->netdev->stats.tx_bytes += skb->len - tx_skb->fcs_len;
queue->stats.tx_bytes += skb->len - tx_skb->fcs_len;
packets++;
bytes += skb->len;
}
@ -2199,7 +2199,8 @@ static void macb_poll_controller(struct net_device *netdev)
static unsigned int macb_tx_map(struct macb *bp,
struct macb_queue *queue,
struct sk_buff *skb,
unsigned int hdrlen)
unsigned int hdrlen,
u8 fcs_len)
{
unsigned int f, nr_frags = skb_shinfo(skb)->nr_frags;
unsigned int len, i, tx_head = queue->tx_head;
@ -2284,6 +2285,7 @@ static unsigned int macb_tx_map(struct macb *bp,
/* This is the last buffer of the frame: save socket buffer */
tx_skb->skb = skb;
tx_skb->fcs_len = fcs_len;
/* Update TX ring: update buffer descriptors in reverse order
* to avoid race condition
@ -2417,6 +2419,7 @@ static inline int macb_clear_csum(struct sk_buff *skb)
return 0;
}
/* Returns a negative errno, or the FCS bytes appended (0 or ETH_FCS_LEN). */
static int macb_pad_and_fcs(struct sk_buff **skb, struct net_device *netdev)
{
bool cloned = skb_cloned(*skb) || skb_header_cloned(*skb) ||
@ -2465,7 +2468,7 @@ static int macb_pad_and_fcs(struct sk_buff **skb, struct net_device *netdev)
skb_put_u8(*skb, (fcs >> 16) & 0xff);
skb_put_u8(*skb, (fcs >> 24) & 0xff);
return 0;
return ETH_FCS_LEN;
}
static netdev_tx_t macb_start_xmit(struct sk_buff *skb,
@ -2478,6 +2481,7 @@ static netdev_tx_t macb_start_xmit(struct sk_buff *skb,
netdev_tx_t ret = NETDEV_TX_OK;
unsigned int hdrlen;
unsigned long flags;
int fcs_len;
bool is_lso;
if (macb_clear_csum(skb)) {
@ -2485,7 +2489,8 @@ static netdev_tx_t macb_start_xmit(struct sk_buff *skb,
return ret;
}
if (macb_pad_and_fcs(&skb, netdev)) {
fcs_len = macb_pad_and_fcs(&skb, netdev);
if (fcs_len < 0) {
dev_kfree_skb_any(skb);
return ret;
}
@ -2548,7 +2553,7 @@ static netdev_tx_t macb_start_xmit(struct sk_buff *skb,
}
/* Map socket buffer for DMA transfer */
if (macb_tx_map(bp, queue, skb, hdrlen)) {
if (macb_tx_map(bp, queue, skb, hdrlen, fcs_len)) {
dev_kfree_skb_any(skb);
goto unlock;
}