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Restructure docs: per-device directories under modules/ and nics/ with co-located datasheets, state centralized in state.md, prose tightened into lists and tables

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flamingcow
2026-08-12 19:23:02 -07:00
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docs/nics/x520/README.md
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# Intel X520-DA2 (82599, ixgbe)
The only *certain* arbitrary-framing module-I2C transport (bit-banged, no firmware in the path) — the diagnostics workhorse. Cannot run the committed measurement path — PTP-only RX timestamping ([../../open-questions.md](../../open-questions.md) §2) — unless the bucket-timestamping exploration validates an equivalent.
- PCIe Gen2 ×8 (5 GT/s, 32 Gb/s) — enough for 2×10G full duplex at the default mix.
- **`allow_unsupported_sfp=1` is mandatory** (`ixgbe_main.c:165`): the FS module's honest 10GBASE-T EEPROM fails Intel qualification and kills the whole port probe (error -95, no netdev). `load-ixgbe` passes it.
## `sff_i2c` diagnostics transport (patched driver, validated)
Patched ixgbe (`~/work/ixgbe-sff/`) adds `ixgbe_i2c_raw_write`/`ixgbe_i2c_raw_read` (`ixgbe_phy.c`) — arbitrary START…STOP transactions from the driver's bit-bang primitives, swfw-semaphore bracketed — behind `/sys/kernel/debug/ixgbe/<pci>/sff_i2c` (`w <addr8> <bytes…>` / `r <addr8> <n>`).
- **SDA-release fix (required)**: multi-byte reads returned only byte 0 — the master's ACK left SDA driven low and nothing released it (stock 82599 paths never clock in more than one byte, so the missing release was invisible). `raw_read` releases SDA after each ACK, mirroring stock's release block after clocking out a byte.
- **Two-master windows**: each debugfs op takes the semaphore separately; serialization against the driver's own I2C holds per-op, but multi-op protocol sequences have unlocked gaps, and driver I2C is event-driven (SFP identify, link setup, `ethtool -m`) — firing exactly around cable swaps. Hardening item: a compound op under one semaphore hold ([../../open-questions.md](../../open-questions.md) §4).
## Timestamping facts
- RX latches **PTP frames only** (`TYPE_ALL`/TSIP are X550+; `HWTSTAMP_FILTER_ALL` → -ERANGE, `ixgbe_ptp.c:1043`): one latch pair (RXSTMPL/H, locked until RXSTMPH read), attribute capture (RXSATRL/H), no RX-descriptor timestamp field.
- Per-port free-running SYSTIME (~6.4 ns at 10G), one shared crystal — two-way exchange cancels the inter-port offset.
- Per-queue hardware counters QPRC/QBRC (16 slots via RQSMR, **read-clear**, `ixgbe_main.c:7777,7787`) count at queue write-back, upstream of ring residence — the basis of bucket-exploration route 1.
- Full analysis and bench pokes: [../../open-questions.md](../../open-questions.md) §2.
## RX steering facts
- ntuple ETHER_FLOW is rejected (`ixgbe_flowspec_to_flow_type`: TCP/UDP/SCTP-v4 and IPv4 only) — the tool fails at startup as committed.
- **ETQF/ETQS L2 EtherType filters are the answer on paper**: dedicated ethertype→queue stage ahead of RSS/fdir, 8 slots, 7 free (index 3 reserved for 1588). Flow Director cannot match non-IP frames at all. Analysis and patch shape: [../../open-questions.md](../../open-questions.md) §1.