From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f45.google.com (mail-pj1-f45.google.com [209.85.216.45]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 69A183AB490 for ; Tue, 26 May 2026 20:23:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.45 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779826987; cv=none; b=OLLC1asyZOyrl5DSXn9WwJsmKPI6x78XQD2CnuXphu1FxZUFfCFFPSDv0KWc1pe96KOCM23IvOzuO7hKMlyleAHOTSGqYAm8FI0Y/OnQHAR/F283nKiNv9fUvdT4IpU/qcNSMGTdBzxYORKkWDv1fZ/lNmZdIMJUPXkF8wAVT74= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779826987; c=relaxed/simple; bh=TRyFeOjEFg9Z4oD9ybe51Hvm1Kn6K0WGSxcwfFiQJCM=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=teSHs2BiDhzeIlMt1NxgWKEkgtB+COvwnRQ7P6su8JbH3y2jT0EaqFnJoqfg5V0RSlm5B7BNYzAnXuLJjgIBz2liuGOj6WJ3fOlHD0w/RbeRkmcpfn3xd+4zV8QLOl2HeVjsjT0UDRMBepnRTW+Xl54G2wYKkVCk55jfWebJpF4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=aT2qID+N; arc=none smtp.client-ip=209.85.216.45 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="aT2qID+N" Received: by mail-pj1-f45.google.com with SMTP id 98e67ed59e1d1-366330b6751so8620109a91.1 for ; Tue, 26 May 2026 13:23:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1779826986; x=1780431786; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=M3mXtq2h7QJnUw/yzmR3z22pM1IqybeYG7SOGc1FU/E=; b=aT2qID+NCWvV+KIwCvVS94In0rwK9EOHT02vqhflSyEaGc922A6QKMATwUag/oFGDj FKF37CvsqUSmjsDMaOZocPGO+dWi9hxCB/Dr5uYcQvEr3M52Qigs5nuQjO9biX61sKeM NbB/s2zZOvn3dbmn4BmQj2MvDcPQOqfZbPpqX0BlR/1Tdf92skeRutSMYkjv4is/oPtk kfMo+YX/8Sb1PXJTBxqrW3c1nbp7yQUgOPn9bSKjj/upexg4F3+Dh3qgxqsFKGSVP7h5 Fr2ZmGyeI6uvG8k7Qw84Bu/h7pHj1FSriubcjeXBQS700m8EW2IYqzEXOSXTXfI1vSU5 dP8g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1779826986; x=1780431786; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=M3mXtq2h7QJnUw/yzmR3z22pM1IqybeYG7SOGc1FU/E=; b=epHmzeypRJs51Ss6U+GQyHDCXJWv+9z7CRB2Rv1l27EYeSPXi4SSvg1OB4hCgoJNw/ 3nLmNBsvGr65AE0uysZO8X4au4i4wfjZisUMW1TK7x03voq9X5sxEz5UfLM4Qdrrh1rD 5FHcC0aneiDD8cbR/G9XFKwHtdafJnzaIQzGU9Ic2z7qr1UCc5Ow2lK1RiafxzT/gROo tYW+de6cqNwatlzWWp/OzEdDTd4Lc/OScwoQjEu/OMTTdJp/TNVA9ZpI80kxW5SIM/iw /BOWKsa4A+6f+PS9t0smE/v1laN4rw5iKUu+veqxVu0wQJ+p/8n6iuueIRIiO9Xdx3Xx 5E9A== X-Gm-Message-State: AOJu0YyH2E51WLBoc/Q6MCHftp8iUv2K+mwI8tvLD3LcguxgWhbciQii gXH29KTw7X844p/nA9OayBw9pQbsK/FFbYyMcIDb+9OfLeiQ1ckkfgNTETPTg697 X-Gm-Gg: Acq92OFxBud9mzBHd52m7PRTitbHPcempkjc7BldYneUpe0jaywjhOc59Ocj47E7aeS 4yZQmbkWpM0VQ4hnHkWeTrA40myHfDLxLezOvbG5ZFtD+BhVcxA7JqFvjT6L6DuuUXFTF9QDKEh vHFylJz67f1apxz5K7iDhl5812W2l/X5jSBcuJtHi+lV0sMfRYKJP26Lnw8VV77MFS+D8pl2n83 lOQKFWSKgJPFlaNwz5Uzlmg3L+noUJsY2G1ezox8iNrt1+N9Unp2KMHTL7wcx5nsTXoWgxRPfhp dM2XYAccek2siMZdcFgNpYhRDyaCo3uofAQv4x+Dqq4dCXSvqD/TeOVTUMsmo0nadRHfA6rWHS6 qII3NNInlC9tQgs5XOF84CKtJnwnrP7QtJZNTrfjpOlQ5+6VTzRrPo9uwRKZiUpxzZWmHEY7J/z JsY5KhZDdcsoTW/txjklO9uK33T4/1Vq5pZJKXSRfrBohsdpGPN0TyNs6602YMzTDsK72a4YGaS 85ZjYZ8vvyrUfbT0u97jih7I2303XwD7o8= X-Received: by 2002:a17:90a:fc44:b0:369:bddb:79b5 with SMTP id 98e67ed59e1d1-36a676dc2d0mr21013700a91.2.1779826985725; Tue, 26 May 2026 13:23:05 -0700 (PDT) Received: from ryzen ([2601:644:8000:5b5d:7285:c2ff:fe45:8a32]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-36a721c7b92sm13280442a91.12.2026.05.26.13.23.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 26 May 2026 13:23:05 -0700 (PDT) From: Rosen Penev To: netdev@vger.kernel.org Cc: Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , linux-kernel@vger.kernel.org (open list) Subject: [PATCH net-next] net: ibm: emac: Reserve VLAN header in MJS limit Date: Tue, 26 May 2026 13:22:47 -0700 Message-ID: <20260526202247.13823-1-rosenp@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The IBM EMAC programs its Maximum Jumbo Size (MJS) drop threshold from ndev->mtu directly. The hardware sizes the threshold against the L2 frame minus the ethernet header, but does not discount the 802.1Q tag, so a frame carrying a VLAN tag and a full 1500-byte payload exceeds MJS by exactly 4 bytes and is dropped. This is normally hidden because JPSM (and therefore the MJS check) only engages when the MTU is raised above ETH_DATA_LEN. With the qca8k DSA tagger the conduit MTU is bumped by QCA_HDR_LEN to 1502 during dsa_conduit_setup(), which is enough to enable JPSM and expose the off-by-VLAN-tag in the limit. Pad MJS by VLAN_HLEN so a VLAN-tagged full-MTU frame passes. Reported on Meraki MX60 (qca8k switch): tagged VLAN traffic drops at 1500-byte payload, while 1496 bytes works and untagged 1500 bytes works. Assisted-by: Claude:Opus-4.7 Signed-off-by: Rosen Penev --- drivers/net/ethernet/ibm/emac/core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/net/ethernet/ibm/emac/core.c b/drivers/net/ethernet/ibm/emac/core.c index 11d673a9f119..90471cff37dd 100644 --- a/drivers/net/ethernet/ibm/emac/core.c +++ b/drivers/net/ethernet/ibm/emac/core.c @@ -30,6 +30,7 @@ #include #include #include +#include #include #include #include @@ -457,7 +458,7 @@ static inline u32 emac_iff2rmr(struct net_device *ndev) if (emac_has_feature(dev, EMAC_APM821XX_REQ_JUMBO_FRAME_SIZE)) { r &= ~EMAC4_RMR_MJS_MASK; - r |= EMAC4_RMR_MJS(ndev->mtu); + r |= EMAC4_RMR_MJS(ndev->mtu + VLAN_HLEN); } return r; -- 2.54.0