From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.tipi-net.de (mail.tipi-net.de [194.13.80.246]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 02E50349B1C; Mon, 31 Aug 2026 11:31:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=194.13.80.246 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788175918; cv=none; b=MQDkZqfiUp344ytAlaB2csm9YgGLEc7FquchEllPPeDrRfHfXv1nARAQ1gLTbToGL2WBJooups8pKeU37HzMktEUykGoW1Ik9S+jlombq2FFyKyTQRLdLIDmgmTlY3oXsyEclXd5L004KUsUtkE38uyYPQ8QOcCvfBkYEJTfxsw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788175918; c=relaxed/simple; bh=WBYSbjAyJMar+AWDYIJVYt2kwpVmbrEuRdJTtUfwa+I=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=c6NZ80JWF6zjUTN1OOhJZv/XxWv6NogH3uLeIEJr5acLqo84RkN8QDkJL5g98hYzJ0PJfWpToXAnkMoXCVZQvDUNZv9PTmN1D2EoaeHok1YEtvnp26jf8rav7j8CYHSB98gvGbsPlHcfuWR4oueRR+oHjNnvOcCBk4N1gtYqQkQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=tipi-net.de; spf=pass smtp.mailfrom=tipi-net.de; dkim=pass (2048-bit key) header.d=tipi-net.de header.i=@tipi-net.de header.b=eKNOlAPX; arc=none smtp.client-ip=194.13.80.246 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=tipi-net.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=tipi-net.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=tipi-net.de header.i=@tipi-net.de header.b="eKNOlAPX" Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id C4627A3C01; Mon, 31 Aug 2026 13:31:47 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=tipi-net.de; s=dkim; t=1788175910; h=from:subject:date:message-id:to:cc:mime-version: content-transfer-encoding; bh=ikqKP7N4gfkljOC5wiO0qpzCYoDu6acU4F3h7XHJdX4=; b=eKNOlAPXphB57yUnkms4F+M5xtW5q6CN2qvGYpznAORw5LZ/RsGpPPsmAVkTkDIK+Kh7pL wA87/e/ejHw7HnezVyRdg9fi1qFkYmlAeEGqWRnnzs9DTTdg61FdwTE+dSSNEBOLduAC6R AOHjTDFZiIA8ZfyFBKIErlFzhCiBdqzDi0gdT6ooEbuBBKtkAvrtd/FoZZG/UdU3kkJnpQ JwGBpDUTe2mVnLVggV/UykDVsnAer3JUdYmNUWDg1nwMUsVkaZ1voevYBvd0HTa3pca95q FAgFMnWdsrruHzqb+PFsoYnjXVoJf4c4C8ozJHpTRwdxb0R5Jl4QXzrFWodGYA== From: Nicolai Buchwitz To: netdev@vger.kernel.org, =?UTF-8?q?Th=C3=A9o=20Lebrun?= Cc: Conor Dooley , Andrew Lunn , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , David Laight , linux-kernel@vger.kernel.org, Nicolai Buchwitz Subject: [PATCH net] net: macb: exclude software FCS from TX byte statistics Date: Mon, 31 Aug 2026 13:31:28 +0200 Message-ID: <20260831113128.1678674-1-nb@tipi-net.de> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Last-TLS-Session-Version: TLSv1.3 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: 653e92a9175e ("net: macb: add support for padding and fcs computation") Signed-off-by: Nicolai Buchwitz --- Originally patch 1/2 of "net: macb: fix zero UDPv4 checksum on transmit" [1], split out into its own patch since it's a pre-existing, partly related issue, as suggested by Paolo and David. [1] https://lore.kernel.org/all/20260824134703.766708-1-nb@tipi-net.de/ drivers/net/ethernet/cadence/macb.h | 3 +++ drivers/net/ethernet/cadence/macb_main.c | 21 +++++++++++++-------- 2 files changed, 16 insertions(+), 8 deletions(-) diff --git a/drivers/net/ethernet/cadence/macb.h b/drivers/net/ethernet/cadence/macb.h index 1e1f52285a39..d6931c41f39d 100644 --- a/drivers/net/ethernet/cadence/macb.h +++ b/drivers/net/ethernet/cadence/macb.h @@ -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; }; diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c index 76ee4f506033..b1939da4c95a 100644 --- a/drivers/net/ethernet/cadence/macb_main.c +++ b/drivers/net/ethernet/cadence/macb_main.c @@ -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; } -- 2.53.0