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[144.49.247.120]) by smtp-relay.gmail.com with ESMTPS id 98e67ed59e1d1-3ab397918efsm2668167a91.4.2026.10.12.14.50.03 for (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 12 Oct 2026 14:50:03 -0700 (PDT) X-Relaying-Domain: broadcom.com X-CFilter-Loop: Reflected Received: by mail-dy1-f200.google.com with SMTP id 5a478bee46e88-34ef0362d95so3421799eec.1 for ; Mon, 12 Oct 2026 14:50:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=broadcom.com; s=google; t=1791841802; x=1792446602; darn=vger.kernel.org; h=content-transfer-encoding:content-type:in-reply-to:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:from:to:cc:subject:date:message-id:reply-to :content-type; bh=//4tECdi8BFJKV6WG98OoZqesXX7E4bq+4mUAnkqPdA=; b=gLRgG5JfABefTspfRGXUszzuVV8b8u1Y5y6uNo5pMLNE2tifMlT9rEqcG2J33E07wL keM99okg8eTxGIiipU/nyUPL2mClZ0V2a49oW2VEdRX2DdZLbKh+t2ByU0jadevBNCdS APbqvMtOrx7d3QqG+V1bjf1n+7vWGMz1uSwk8= X-Forwarded-Encrypted: i=1; AKwUvBxGNXLqVS1W1Y8fi0H2CXVa/KJVHiu7NxnXlXHHnxj4QX3TCpWsoT5AmCMjpE+ha2CBuqtjqgjUGa6p8ak=@vger.kernel.org X-Received: by 2002:a05:7022:1605:b0:151:94a6:6f5f with SMTP id a92af1059eb24-16a5fc917b4mr17679590c88.10.1791841801538; Mon, 12 Oct 2026 14:50:01 -0700 (PDT) X-Received: by 2002:a05:7022:1605:b0:151:94a6:6f5f with SMTP id a92af1059eb24-16a5fc917b4mr17679544c88.10.1791841800836; Mon, 12 Oct 2026 14:50:00 -0700 (PDT) Received: from [10.67.48.245] ([192.19.223.252]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-169a620bdafsm42915443c88.23.2026.10.12.14.49.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 12 Oct 2026 14:50:00 -0700 (PDT) Message-ID: <9767d40a-7926-42a5-8acd-67183a68f8d1@broadcom.com> Date: Mon, 12 Oct 2026 14:49:58 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v4 8/8] net: bcmgenet: reassemble jumbo frames from status block fragments To: Nicolai Buchwitz , Doug Berger , Broadcom internal kernel review list , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Dave Stevenson , Justin Chen , Pierre-Marin Leclercq , Florian Fainelli References: <20261012-nb-genet-mtu-nn-v2-v4-0-2e2e3bfaf8cc@tipi-net.de> <20261012-nb-genet-mtu-nn-v2-v4-8-2e2e3bfaf8cc@tipi-net.de> Content-Language: en-US, fr-FR From: Florian Fainelli Autocrypt: addr=florian.fainelli@broadcom.com; keydata= xsBNBFPAG8ABCAC3EO02urEwipgbUNJ1r6oI2Vr/+uE389lSEShN2PmL3MVnzhViSAtrYxeT M0Txqn1tOWoIc4QUl6Ggqf5KP6FoRkCrgMMTnUAINsINYXK+3OLe7HjP10h2jDRX4Ajs4Ghs JrZOBru6rH0YrgAhr6O5gG7NE1jhly+EsOa2MpwOiXO4DE/YKZGuVe6Bh87WqmILs9KvnNrQ PcycQnYKTVpqE95d4M824M5cuRB6D1GrYovCsjA9uxo22kPdOoQRAu5gBBn3AdtALFyQj9DQ KQuc39/i/Kt6XLZ/RsBc6qLs+p+JnEuPJngTSfWvzGjpx0nkwCMi4yBb+xk7Hki4kEslABEB AAHNMEZsb3JpYW4gRmFpbmVsbGkgPGZsb3JpYW4uZmFpbmVsbGlAYnJvYWRjb20uY29tPsLB IQQQAQgAywUCZWl41AUJI+Jo+hcKAAG/SMv+fS3xUQWa0NryPuoRGjsA3SAUAAAAAAAWAAFr ZXktdXNhZ2UtbWFza0BwZ3AuY29tjDAUgAAAAAAgAAdwcmVmZXJyZWQtZW1haWwtZW5jb2Rp bmdAcGdwLmNvbXBncG1pbWUICwkIBwMCAQoFF4AAAAAZGGxkYXA6Ly9rZXlzLmJyb2FkY29t Lm5ldAUbAwAAAAMWAgEFHgEAAAAEFQgJChYhBNXZKpfnkVze1+R8aIExtcQpvGagAAoJEIEx tcQpvGagWPEH/2l0DNr9QkTwJUxOoP9wgHfmVhqc0ZlDsBFv91I3BbhGKI5UATbipKNqG13Z TsBrJHcrnCqnTRS+8n9/myOF0ng2A4YT0EJnayzHugXm+hrkO5O9UEPJ8a+0553VqyoFhHqA zjxj8fUu1px5cbb4R9G4UAySqyeLLeqnYLCKb4+GklGSBGsLMYvLmIDNYlkhMdnnzsSUAS61 WJYW6jjnzMwuKJ0ZHv7xZvSHyhIsFRiYiEs44kiYjbUUMcXor/uLEuTIazGrE3MahuGdjpT2 IOjoMiTsbMc0yfhHp6G/2E769oDXMVxCCbMVpA+LUtVIQEA+8Zr6mX0Yk4nDS7OiBlvOwE0E U8AbwQEIAKxr71oqe+0+MYCc7WafWEcpQHFUwvYLcdBoOnmJPxDwDRpvU5LhqSPvk/yJdh9k 4xUDQu3rm1qIW2I9Puk5n/Jz/lZsqGw8T13DKyu8eMcvaA/irm9lX9El27DPHy/0qsxmxVmU pu9y9S+BmaMb2CM9IuyxMWEl9ruWFS2jAWh/R8CrdnL6+zLk60R7XGzmSJqF09vYNlJ6Bdbs MWDXkYWWP5Ub1ZJGNJQ4qT7g8IN0qXxzLQsmz6tbgLMEHYBGx80bBF8AkdThd6SLhreCN7Uh IR/5NXGqotAZao2xlDpJLuOMQtoH9WVNuuxQQZHVd8if+yp6yRJ5DAmIUt5CCPcAEQEAAcLB gQQYAQIBKwUCU8AbwgUbDAAAAMBdIAQZAQgABgUCU8AbwQAKCRCTYAaomC8PVQ0VCACWk3n+ obFABEp5Rg6Qvspi9kWXcwCcfZV41OIYWhXMoc57ssjCand5noZi8bKg0bxw4qsg+9cNgZ3P N/DFWcNKcAT3Z2/4fTnJqdJS//YcEhlr8uGs+ZWFcqAPbteFCM4dGDRruo69IrHfyyQGx16s CcFlrN8vD066RKevFepb/ml7eYEdN5SRALyEdQMKeCSf3mectdoECEqdF/MWpfWIYQ1hEfdm C2Kztm+h3Nkt9ZQLqc3wsPJZmbD9T0c9Rphfypgw/SfTf2/CHoYVkKqwUIzI59itl5Lze+R5 wDByhWHx2Ud2R7SudmT9XK1e0x7W7a5z11Q6vrzuED5nQvkhAAoJEIExtcQpvGagugcIAJd5 EYe6KM6Y6RvI6TvHp+QgbU5dxvjqSiSvam0Ms3QrLidCtantcGT2Wz/2PlbZqkoJxMQc40rb fXa4xQSvJYj0GWpadrDJUvUu3LEsunDCxdWrmbmwGRKqZraV2oG7YEddmDqOe0Xm/NxeSobc MIlnaE6V0U8f5zNHB7Y46yJjjYT/Ds1TJo3pvwevDWPvv6rdBeV07D9s43frUS6xYd1uFxHC 7dZYWJjZmyUf5evr1W1gCgwLXG0PEi9n3qmz1lelQ8lSocmvxBKtMbX/OKhAfuP/iIwnTsww 95A2SaPiQZA51NywV8OFgsN0ITl2PlZ4Tp9hHERDe6nQCsNI/Us= In-Reply-To: <20261012-nb-genet-mtu-nn-v2-v4-8-2e2e3bfaf8cc@tipi-net.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-DetectorID-Processed: b00c1d49-9d2e-4205-b15f-d015386d3d5e On 10/12/26 02:00, Nicolai Buchwitz wrote: > The hardware does not truncate a frame longer than the packet ready > threshold. It splits the frame across descriptors and writes a status block > at the start of each one. The first fragment then arrives with SOP and no > EOP and is dropped as fragmented. This caps the MTU. > > Strip the status blocks and reassemble the fragments. Only the last block > holds the checksum of the whole frame. Broadcom confirmed from the RTL that > every GENET revision splits long frames this way, not just the v5 this was > tested on. > > On transmit the MAC only checksums a frame it holds in full, so anything > longer than the threshold falls back to software. At jumbo sizes the larger > frame saves more per packet overhead than the checksum costs. > > UMAC_MAX_FRAME_LEN is 14 bit and counts the FCS. That puts the maximum MTU > at 16347. > > The TX descriptor length field is wider than DMA_BUFLENGTH_MASK suggests, > that mask only extracts the length from the RX status word. A frame of > 16361 bytes, the largest that MTU allows, came back byte exact 200 times > over UMAC loopback. > > Suggested-by: Justin Chen > Tested-by: Pierre-Marin Leclercq > Signed-off-by: Nicolai Buchwitz Reviewed-by: Florian Fainelli -- Florian