macb1 checksum fixes - #7552
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Does this force a software checksum for all packets? Can't it just fix up the special case? (And it's @pelwell) |
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No, UDP only. Fixing up the special case would mean computing the full checksum in software anyway, and AFAIU the hardware inserts the value in flight, so the driver never sees it. I'll dig through the public AT91 / Zynq docs anyway, maybe there's a useful register after all. If you have access to ressources, pointers are welcome. |
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Perhaps someone else could pitch in - I'm OoO for a while |
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Enjoy, well deserved! |
Frames going through macb_pad_and_fcs() get padded and four FCS bytes appended, and TX completion then accounts the grown skb->len. tx_bytes is supposed to exclude the FCS, and frames padded by the hardware are counted without the padding anyway, so these frames show up too large in the statistics. Remember the length the stack handed over and use that for the byte counters. BQL stays on the padded skb->len that netdev_tx_sent_queue() saw. Fixes: 653e92a ("net: macb: add support for padding and fcs computation") Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>
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The GEM checksum engine writes its raw result into the UDP checksum field, so a UDPv4 checksum that computes to zero goes out as 0x0000. RFC 768 requires: If the computed checksum is zero, it is transmitted as all ones (the equivalent in one's complement arithmetic). An all zero transmitted checksum value means that the transmitter generated no checksum (for debugging or for higher level protocols that don't care). So these packets lose their integrity check and peers treat them as sent without a checksum. Raspberry Pi confirmed in a simulation of the Cadence IP [1] that the engine skips the final substitution exactly for UDP over IPv4. UDPv6 and TCP come out correct. The IP changelog shows no related change, so probably all GEM revisions have the same bug. Clear the checksum offload features for UDPv4 frames in macb_features_check(), the core then completes the checksum in software before handing the frame over. With ip_summed cleared, macb_pad_and_fcs() appends the FCS and the TX_NOCRC descriptor bit keeps the hardware off the frame. TCP and UDPv6 keep the offload. One-step PTP sync packets keep the hardware path because the MAC rewrites their timestamp during transmit, which would invalidate a software checksum. Leave their existing checksum handling unchanged. [1] raspberrypi#7550 (comment) Fixes: 85ff3d8 ("net/macb: add TX checksum offload feature") Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>
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I've re-run workflows. Checkpatch has a single complaint, otherwise it's available for testing via |
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fe4dd47 is a candidate for fixing #7550. The other patch fixes a stats issue and i plan to submit it in the same series upstream once I got confirmation that it fixes the issue
@pellwell, can you please trigger the builds? Thanks.