i2c-imc-skylake: implement Receive Byte and Send Byte
The engine encodes an address-only transaction in command word bit 18, which is what SMBus Receive Byte and Send Byte need and what was missing for ee1004 to bind. The bit is not documented for the PCU function. It was located by structure rather than by sweeping: SMBCMD on the iMC channel function (datasheet ref. 614073 section 3.1.8) places PNTR_SEL immediately above WORD_ACCESS, and word access here is bit 17. Bit 17 had itself been unknown until it turned out to be word access, and an earlier sweep of this register covered bits 31:20 only, so 18 was untried rather than already ruled out. Validated against the device rather than against the register. An EEPROM auto-increments its pointer after a read, so priming the pointer and repeating the read with the bit set has a predicted answer: the next byte, not the one named. Eight consecutive reads returned SPD bytes 0x01 through 0x08 in order, matching an ordinary dump. Send Byte was confirmed on the DDR4 page-select addresses, which hold a latch and store no data, so the page state is itself the readout. Result: ee1004 binds on all four SPD addresses and decode-dimms decodes all four modules with both CRCs valid on each. The part number comes off page 1, so the page select runs end to end. The four module serial numbers are unchanged from the baseline recorded before this series. SMBus Quick stays unimplemented. Beyond having no obvious encoding, a write into the 0x30-0x37 range is how an EE1004 SPD is write-protected, permanently on many modules, so an adapter on the memory bus should not advertise a probe that writes. i2cdetect scans in read mode. Also fix test-smoke.sh resolving the module through modinfo, which silently tested the installed DKMS build instead of the one just compiled. It now prefers the local .ko and prints which it loaded. Smoke suite: 19 passed, 0 failed. checkpatch --strict 0/0/0, in-tree W=1 and Sparse clean.
This commit is contained in:
Simone
@@ -64,3 +64,72 @@ Two results matter:
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Requirements: `msr-tools` (`rdmsr`), `pciutils` (`setpci`, `lspci`), and the
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`msr` module (`modprobe msr`).
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## 4. `probe-cf8-transaction.sh` — does CF8/CFC start a transfer? (WRITES TO HARDWARE)
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Follow-up to §3. `probe-cf8-write.sh` shows whether the register accepts a
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value; this shows whether the engine acts on it, by setting the GO bit for a
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read of an unpopulated address and watching STATUS.
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```bash
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sudo ./tools/probe-cf8-transaction.sh --i-understand
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```
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It does start one. That result retired the plan to reach these registers
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through ECAM with a PCI-core change, and the driver uses the ordinary config
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accessors.
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## 5. `probe-imc-documented.sh` — the interface Intel documents (WRITES TO HARDWARE)
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Issues a read through `SMB_STAT`/`SMBCMD`/`SMBCNTL` on the iMC channel
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functions (`8086:2040`), the interface the datasheet describes, rather than the
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PCU registers this driver uses.
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```bash
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sudo ./tools/probe-imc-documented.sh --i-understand
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```
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On the development board it reports `RDO=1, SBE=0, RDATA=0x00` identically for
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a populated 0x50, a populated 0x52 and an absent 0x57: it completes but cannot
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tell a populated slot from an empty one, so it is not reaching this bus.
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## 6. `probe-pntr-sel.sh` — find the address-only bit (read-only on the bus)
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Finds the command-word bit that suppresses the register byte, which is what
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SMBus Receive Byte and Send Byte need.
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```bash
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sudo ./tools/probe-pntr-sel.sh --i-understand --channel 1
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```
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Not a blind sweep. An EEPROM auto-increments its pointer after a read, so
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priming the pointer with an ordinary read and then repeating it with the
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candidate bit set has a predicted answer: the *next* byte, not the one named.
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The script checks that prediction at two different offsets and then walks eight
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consecutive reads, which an ordinary dump must reproduce exactly.
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The answer on this engine is bit 18, matching the position of `PNTR_SEL`
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relative to `WORD_ACCESS` in the documented `SMBCMD` layout. Reads only, and
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never to the page-select addresses, so the DDR4 page latch does not move.
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## 7. `probe-send-byte.sh` — the write half (WRITES TO HARDWARE)
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Confirms the same bit produces a Send Byte, against the page-select addresses
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`0x36`/`0x37`. Those hold a latch and store no data, so the only thing a write
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there can do is choose which half of the SPD is visible — and that choice is
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itself the readout, since byte 0x00 is the JEDEC `0x23` on page 0 and something
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else on page 1. Nothing is written to `0x50`-`0x57`.
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```bash
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sudo ./tools/probe-send-byte.sh --i-understand --channel 0 --restore
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```
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`--restore` is the safe first run: it targets a channel already stuck on page 1
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and selects page 0, so a working Send Byte repairs that channel and a broken one
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leaves it exactly as found. There is no outcome worse than the starting state.
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`--flip` does the full round trip on a healthy channel, after `--restore` has
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shown the encoding works.
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A channel found on page 1 is not a fault of this driver: `ee1004`, and
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OpenRGB's `DDR4DirectAccessor::set_page()`, both select a page and leave it
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selected.
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Executable
+221
@@ -0,0 +1,221 @@
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#!/usr/bin/env bash
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#
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# READ-ONLY ON THE BUS. Tests whether the unexplored bits of the PCU command
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# word encode an address-only ("pointer select") transaction, which is what
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# SMBus Receive Byte and Send Byte need and what this driver cannot express
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# today.
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#
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# Why bit 18 in particular. The command word bits the driver knows are:
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#
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# b29 engine enable b20 TSOD active b19 GO b17 word access
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# b15 write b14:8 address b7:0 register
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#
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# The interface Intel does document for the iMC channel functions (SMBCMD,
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# datasheet ref. 614073 section 3.1.8) lays its control bits out as:
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#
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# b31 CMD_TRIGGER b30 PNTR_SEL b29 WORD_ACCESS b28:27 rw
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#
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# There PNTR_SEL sits immediately above WORD_ACCESS. In the PCU word, word
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# access is bit 17, so the same adjacency puts a pointer-select bit at 18.
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# Bit 17 was itself unexplored until it turned out to be word access, so the
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# guess has precedent on this engine.
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#
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# An earlier sweep of this register (2026-06-12, furyrs docs/linux-rgb-protocol.md)
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# covered bits 31:20 only, so 16 and 18 have never been tried. Both are swept
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# here.
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#
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# The test is a discriminator, not a bit flip in the dark. SPD 0x50 answers
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# with known values, and an EEPROM auto-increments its internal pointer after
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# a read. So:
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#
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# 1. ordinary read of register 0x00 -> 0x23, pointer left at 0x01
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# 2. same read with the candidate bit set
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# - returns something other than 0x23 -> the register byte was not
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# sent, the engine read from the pointer: address-only transaction
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# - returns 0x23 again -> the bit changed nothing
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#
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# Repeated at register 0x02 (-> 0x0c) so a single coincidence cannot pass.
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#
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# Nothing is written to the bus: reads only, against an EEPROM, and never to
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# the page-select addresses 0x36/0x37, so the global DDR4 page latch does not
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# move. DATA is restored with GO masked on every exit path.
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#
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set -euo pipefail
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# shellcheck source=tools/common.sh
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source "$(dirname "$(readlink -f "$0")")/common.sh"
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COMMAND_TOGGLE=$((1 << 29))
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GO_BIT=$((1 << 19))
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TSOD_ACTIVE_BIT=$((1 << 20))
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STAT_BUSY=1
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STAT_ERROR=2
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ADDR=0x50
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CHANNEL=0
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CANDIDATES=(16 18)
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WALK=8
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CONFIRMED=false
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while (($#)); do
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case $1 in
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--i-understand) CONFIRMED=true; shift ;;
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--addr) ADDR=$2; shift 2 ;;
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--channel) CHANNEL=$2; shift 2 ;;
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--bits) IFS=, read -r -a CANDIDATES <<<"$2"; shift 2 ;;
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-h|--help)
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sed -n '3,40p' "$0"
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echo "usage: $0 --i-understand [--addr 0xNN] [--channel 0|1] [--bits 16,18]"
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exit 0
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;;
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*) die "unknown argument: $1" ;;
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esac
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done
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$CONFIRMED || {
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echo "Issues SMBus read transactions from userspace. Re-run with --i-understand." >&2
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exit 2
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}
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require_root
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require_cmd lspci setpci awk
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case $CHANNEL in
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0) REG_DATA=$REG_CH0_DATA; REG_STAT=$REG_CH0_STAT; REG_CTRL=$REG_CH0_CTRL ;;
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1) REG_DATA=$REG_CH1_DATA; REG_STAT=$REG_CH1_STAT; REG_CTRL=$REG_CH1_CTRL ;;
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*) die "channel must be 0 or 1" ;;
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esac
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driver_is_loaded && die "unload i2c-imc-skylake first"
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BDF=$(find_pcu)
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original=$(read_reg "$BDF" "$REG_DATA")
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status0=$(read_reg "$BDF" "$REG_STAT")
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((original & GO_BIT)) && die "GO already set, refusing"
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((original & TSOD_ACTIVE_BIT)) && die "TSOD_ACTIVE set, refusing"
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((status0 & STAT_BUSY)) && die "engine BUSY, refusing"
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restore()
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{
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setpci -s "$BDF" "$REG_DATA.L=$(printf '%08x' "$((original & ~GO_BIT))")" || true
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}
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trap restore EXIT
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# read_once <command> -> echoes "<status> <ctrl> <byte>"; returns 1 on NACK.
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read_once()
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{
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local command=$1 i data status ctrl
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setpci -s "$BDF" "$REG_DATA.L=$(printf '%08x' "$command")"
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for ((i = 0; i < 60; i++)); do
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data=$(read_reg "$BDF" "$REG_DATA")
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((data & GO_BIT)) || break
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sleep 0.005
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done
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status=$(read_reg "$BDF" "$REG_STAT")
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ctrl=$(read_reg "$BDF" "$REG_CTRL")
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printf '%s %s 0x%02x\n' "$status" "$ctrl" "$((ctrl & 0xff))"
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! ((status & STAT_ERROR))
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}
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plain()
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{
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printf '%d' $((COMMAND_TOGGLE | GO_BIT | (ADDR << 8) | $1))
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}
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echo "device $BDF channel $CHANNEL, target $ADDR"
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echo "DATA before: $original STATUS before: $status0"
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echo
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echo "=== baseline: ordinary reads, no candidate bit ==="
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declare -A baseline
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for reg in 0x00 0x02; do
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if out=$(read_once "$(plain "$reg")"); then
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baseline[$reg]=${out##* }
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printf ' reg %s -> %s (status %s ctrl %s)\n' \
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"$reg" "${baseline[$reg]}" "${out%% *}" "$(awk '{print $2}' <<<"$out")"
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else
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printf ' reg %s -> NACK (status %s)\n' "$reg" "${out%% *}"
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baseline[$reg]=NACK
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fi
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done
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echo
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verdict=none
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for bit in "${CANDIDATES[@]}"; do
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candidate=$((1 << bit))
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printf '=== candidate BIT(%d) = 0x%08x ===\n' "$bit" "$candidate"
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differed=0
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for reg in 0x00 0x02; do
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# Prime the EEPROM pointer with an ordinary read, then repeat it
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# with the candidate bit set. A pointer-select transaction skips
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# the register byte and answers from the auto-incremented pointer.
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read_once "$(plain "$reg")" >/dev/null || true
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if out=$(read_once "$(( $(plain "$reg") | candidate ))"); then
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byte=${out##* }
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printf ' after reg %s -> %s (baseline %s, status %s)\n' \
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"$reg" "$byte" "${baseline[$reg]}" "${out%% *}"
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[[ "$byte" != "${baseline[$reg]}" ]] && differed=$((differed + 1))
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else
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printf ' after reg %s -> NACK (status %s)\n' "$reg" "${out%% *}"
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differed=$((differed + 1))
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fi
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done
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if ((differed == 2)); then
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echo " -> both reads changed: this bit alters the transaction."
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verdict=$bit
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elif ((differed == 1)); then
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echo " -> one read changed. Not conclusive; could be an SPD byte"
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echo " that happens to equal its neighbour. Re-run to confirm."
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else
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echo " -> identical to baseline: the bit is inert on reads."
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fi
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echo
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done
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# A bit that merely perturbs the answer is not proof of a pointer-select. The
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# proof is that consecutive transactions walk the EEPROM: prime the pointer with
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# an ordinary read, then issue the candidate repeatedly and check the answers
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# follow the device's own byte sequence.
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if [[ "$verdict" != none ]]; then
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candidate=$((1 << verdict))
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printf '=== walk: %d consecutive BIT(%d) reads after priming at 0x00 ===\n' \
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"$WALK" "$verdict"
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read_once "$(plain 0x00)" >/dev/null || true
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walked=()
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for ((i = 0; i < WALK; i++)); do
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if out=$(read_once "$(( $(plain 0x00) | candidate ))"); then
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walked+=("${out##* }")
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else
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walked+=(NACK)
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fi
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done
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printf ' bytes 0x01.. : %s\n' "${walked[*]}"
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echo " compare against an ordinary dump of the same range: if they match,"
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echo " the engine is issuing a genuine address-only read."
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echo
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fi
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echo "=== verdict ==="
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if [[ "$verdict" == none ]]; then
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cat <<-EOF
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NO ADDRESS-ONLY ENCODING FOUND in bits ${CANDIDATES[*]}.
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Every candidate left the transaction unchanged, so the engine still
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sends a register byte. SMBus Receive Byte and Send Byte cannot be
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implemented honestly on this command word, and ee1004 (and therefore
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decode-dimms) stays out of reach through this interface.
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EOF
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else
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cat <<-EOF
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BIT($verdict) CHANGES THE TRANSACTION.
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Both probe reads returned something other than the register they named,
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which is what an address-only transaction looks like. Next step is to
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confirm the returned byte tracks the EEPROM pointer rather than being
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another deterministic transform of the command word: read a known
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sequence of registers and check the answers follow it.
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EOF
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fi
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Executable
+200
@@ -0,0 +1,200 @@
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#!/usr/bin/env bash
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#
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# WRITES TO THE BUS. Tests whether the pointer-select bit found by
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# tools/probe-pntr-sel.sh also produces an SMBus Send Byte, the write half of
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# I2C_FUNC_SMBUS_BYTE, which ee1004 needs to select a DDR4 SPD page.
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#
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# The target is the page-select address 0x36 or 0x37, never an EEPROM. Those
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# addresses hold a single latch and store no data: the only effect a write can
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# have there is to select page 0 or page 1. Nothing is written to 0x50-0x57.
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#
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# The test verifies itself. A DDR4 SPD is 512 bytes reached through a 256-byte
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# window, so which page is latched is visible in the data: on page 0 byte 0x00
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# is 0x23 (the JEDEC "512 byte SPD" code), on page 1 the same offset shows
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# byte 0x100 instead, which is not 0x23. Issue the Send Byte, read byte 0x00
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# back, and the page state is the answer.
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#
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# --restore is the safe first run. It targets a channel already latched on page
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# 1 and selects page 0, so a working Send Byte repairs that channel and a
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# broken one leaves it exactly as it was found. There is no outcome worse than
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# the starting state.
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#
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# --flip runs the full round trip on a channel already on page 0: select page 1,
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# confirm the data moved, select page 0 again, confirm it came back. Use it only
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# after --restore has shown the encoding works.
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#
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set -euo pipefail
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# shellcheck source=tools/common.sh
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source "$(dirname "$(readlink -f "$0")")/common.sh"
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COMMAND_TOGGLE=$((1 << 29))
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GO_BIT=$((1 << 19))
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PNTR_SEL_BIT=$((1 << 18))
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TSOD_ACTIVE_BIT=$((1 << 20))
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WRITE_OPERATION=$((1 << 15))
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STAT_BUSY=1
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STAT_ERROR=2
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SPD_ADDR=0x50
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PAGE0_ADDR=0x36
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PAGE1_ADDR=0x37
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SPD_PAGE0_BYTE0=0x23
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CHANNEL=0
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MODE=restore
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CONFIRMED=false
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while (($#)); do
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case $1 in
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--i-understand) CONFIRMED=true; shift ;;
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--channel) CHANNEL=$2; shift 2 ;;
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--restore) MODE=restore; shift ;;
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--flip) MODE=flip; shift ;;
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-h|--help)
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sed -n '3,24p' "$0"
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echo "usage: $0 --i-understand --channel 0|1 [--restore|--flip]"
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exit 0
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;;
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*) die "unknown argument: $1" ;;
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esac
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done
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$CONFIRMED || {
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echo "This writes to the SPD page-select address. Re-run with --i-understand." >&2
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exit 2
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}
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require_root
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require_cmd lspci setpci awk
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case $CHANNEL in
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0) REG_DATA=$REG_CH0_DATA; REG_STAT=$REG_CH0_STAT; REG_CTRL=$REG_CH0_CTRL ;;
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1) REG_DATA=$REG_CH1_DATA; REG_STAT=$REG_CH1_STAT; REG_CTRL=$REG_CH1_CTRL ;;
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*) die "channel must be 0 or 1" ;;
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esac
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driver_is_loaded && die "unload i2c-imc-skylake first"
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BDF=$(find_pcu)
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original_data=$(read_reg "$BDF" "$REG_DATA")
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original_ctrl=$(read_reg "$BDF" "$REG_CTRL")
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status0=$(read_reg "$BDF" "$REG_STAT")
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((original_data & GO_BIT)) && die "GO already set, refusing"
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((original_data & TSOD_ACTIVE_BIT)) && die "TSOD_ACTIVE set, refusing"
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((status0 & STAT_BUSY)) && die "engine BUSY, refusing"
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restore()
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{
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setpci -s "$BDF" "$REG_DATA.L=$(printf '%08x' "$((original_data & ~GO_BIT))")" || true
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setpci -s "$BDF" "$REG_CTRL.L=$(printf '%08x' "$original_ctrl")" || true
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}
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trap restore EXIT
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# wait_idle -> echoes the final status
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wait_idle()
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{
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local i data
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for ((i = 0; i < 60; i++)); do
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data=$(read_reg "$BDF" "$REG_DATA")
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((data & GO_BIT)) || break
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sleep 0.005
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done
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read_reg "$BDF" "$REG_STAT"
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}
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# spd_byte0 -> echoes the byte at SPD offset 0x00 as 0x%02x
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spd_byte0()
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{
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local ctrl
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setpci -s "$BDF" \
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"$REG_DATA.L=$(printf '%08x' "$((COMMAND_TOGGLE | GO_BIT | (SPD_ADDR << 8)))")"
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wait_idle >/dev/null
|
||||
ctrl=$(read_reg "$BDF" "$REG_CTRL")
|
||||
printf '0x%02x\n' "$((ctrl & 0xff))"
|
||||
}
|
||||
|
||||
# send_byte <addr> -> echoes the status; returns 1 if the device NACKed
|
||||
send_byte()
|
||||
{
|
||||
local addr=$1 command status
|
||||
|
||||
command=$((COMMAND_TOGGLE | GO_BIT | PNTR_SEL_BIT | WRITE_OPERATION | (addr << 8)))
|
||||
# Data byte in the same place a BYTE_DATA write puts it. The page-select
|
||||
# devices ignore it; it is set to zero so nothing meaningful is sent.
|
||||
setpci -s "$BDF" "$REG_CTRL.L=00000000"
|
||||
printf ' Send Byte to %s: command 0x%08x\n' "$addr" "$command"
|
||||
setpci -s "$BDF" "$REG_DATA.L=$(printf '%08x' "$command")"
|
||||
status=$(wait_idle)
|
||||
printf ' status 0x%s\n' "${status#0x}"
|
||||
# A NACK here is expected and harmless: some modules latch the page but
|
||||
# do not acknowledge, which is why ee1004 rechecks instead of giving up.
|
||||
! ((status & STAT_ERROR))
|
||||
}
|
||||
|
||||
echo "device $BDF channel $CHANNEL, mode $MODE"
|
||||
echo "DATA before: $original_data CTRL before: $original_ctrl STATUS: $status0"
|
||||
echo
|
||||
|
||||
before=$(spd_byte0)
|
||||
printf 'SPD 0x50 byte 0x00 before: %s\n' "$before"
|
||||
|
||||
case $MODE in
|
||||
restore)
|
||||
if [[ "$before" == "$SPD_PAGE0_BYTE0" ]]; then
|
||||
die "channel $CHANNEL is already on page 0, nothing to restore (use --flip)"
|
||||
fi
|
||||
echo "channel is not on page 0. Selecting page 0."
|
||||
send_byte "$PAGE0_ADDR" || echo " (device did not ack; checking anyway)"
|
||||
after=$(spd_byte0)
|
||||
printf 'SPD 0x50 byte 0x00 after: %s\n\n' "$after"
|
||||
|
||||
if [[ "$after" == "$SPD_PAGE0_BYTE0" ]]; then
|
||||
cat <<-EOF
|
||||
=== SEND BYTE WORKS ===
|
||||
The page-select address accepted an address-only write: byte 0x00 went
|
||||
from $before to $after, the JEDEC page-0 value. Bit 18 encodes SMBus
|
||||
Send Byte as well as Receive Byte, so I2C_FUNC_SMBUS_BYTE can be
|
||||
implemented honestly and ee1004 can bind.
|
||||
|
||||
Channel $CHANNEL is also back on page 0, which is where it should have
|
||||
been.
|
||||
EOF
|
||||
else
|
||||
cat <<-EOF
|
||||
=== NO PAGE CHANGE ===
|
||||
Byte 0x00 is still $after. Either the write did not reach the bus in
|
||||
Send Byte form, or this channel is not on page 1 for the reason
|
||||
assumed. The channel is exactly as it was found; nothing was made
|
||||
worse. Do not implement Send Byte on this encoding.
|
||||
EOF
|
||||
fi
|
||||
;;
|
||||
flip)
|
||||
[[ "$before" == "$SPD_PAGE0_BYTE0" ]] ||
|
||||
die "channel $CHANNEL is not on page 0 to begin with (byte 0x00 = $before)"
|
||||
|
||||
echo "selecting page 1"
|
||||
send_byte "$PAGE1_ADDR" || echo " (no ack; checking anyway)"
|
||||
flipped=$(spd_byte0)
|
||||
printf 'byte 0x00 on page 1: %s\n\n' "$flipped"
|
||||
|
||||
echo "selecting page 0 again"
|
||||
send_byte "$PAGE0_ADDR" || echo " (no ack; checking anyway)"
|
||||
back=$(spd_byte0)
|
||||
printf 'byte 0x00 restored: %s\n\n' "$back"
|
||||
|
||||
echo "=== result ==="
|
||||
if [[ "$flipped" != "$before" && "$back" == "$before" ]]; then
|
||||
echo "Round trip clean: the page moved and came back. Send Byte confirmed."
|
||||
elif [[ "$back" != "$before" ]]; then
|
||||
echo "WARNING: the channel did not return to page 0 (byte 0x00 = $back)."
|
||||
echo "Re-run with --restore to put it back."
|
||||
else
|
||||
echo "The page never moved. Send Byte is not encoded this way."
|
||||
fi
|
||||
;;
|
||||
esac
|
||||
Reference in New Issue
Block a user