i2c-imc-skylake: split the submission into a PCI patch and the driver
The driver reached the PCU function's config space by walking the ACPI MCFG
table and mapping the ECAM page itself. That is one leaf driver deciding
config-space policy, and no other driver in mainline does it, so it was the
single most likely reason for a NAK.
Move that decision where it belongs: the upstream series is now two patches,
a PCI/x86 accessor that forces the memory-mapped path with the core's
locking, and this driver on top of it. Reviewers on each side now get
something they can act on, and get_maintainer.pl selects the PCI and x86
people by itself.
Correctness work in the same pass:
- the completion bits are latched, so a command the engine never accepted
was indistinguishable from a completed one and returned the previous
transaction's data as valid. Require a positive sign that the engine
acted on the command;
- compare the command registers after every transfer against what the
driver left in them and fail with -EAGAIN on a mismatch. The original
iMC driver had this check and it is what makes an unarbitrated system
detectable instead of silently wrong;
- use the i2c core's suspended-adapter mechanism rather than a private
flag and -EHOSTDOWN;
- use devm_mutex_init(), drop the unnecessary pci_enable_device(), and
return -ENODEV rather than -EPERM from the default-off gate, which was
printing a driver-core error on every boot;
- mask GO when restoring a saved command word.
Stop attributing the dropped CF8/CFC write to System Management Mode. The
only evidence was a boot log line naming the access method, which says
nothing about who filters the write. tools/probe-cf8-write.sh is there to
settle it with an MSR_SMI_COUNT measurement.
Add Documentation/i2c/busses/i2c-imc-skylake.rst, which every other PC SMBus
driver has and which was explicitly asked for on the 2020 iMC thread, the
tools/ scripts for the hardware measurements the submission still owes, and
compat/pci-mmcfg-compat.h so the driver still builds out-of-tree against a
kernel without the new accessor while the source stays byte-identical to the
submitted patch.
This commit is contained in:
Simone
Executable
+128
@@ -0,0 +1,128 @@
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#!/usr/bin/env bash
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#
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# WRITES TO HARDWARE. Answers two questions the submission still owes:
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#
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# 1. does a CF8/CFC dword write to the iMC SMBus command register take
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# effect on this board?
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# 2. does that write raise an SMI?
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#
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# It modifies only the register/offset field, DATA[7:0], while the GO bit is
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# clear, so no SMBus transaction is issued, and it restores the original value
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# on every exit path. It refuses to run if the engine is busy, if a transaction
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# is armed, if TSOD is active, or if the driver is loaded.
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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 "$0")")/common.sh"
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GO_BIT=$((1 << 19))
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TSOD_ACTIVE_BIT=$((1 << 20))
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STAT_BUSY=1
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CHANNEL=0
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CONFIRMED=false
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while (($#)); 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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-h|--help)
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sed -n '3,14p' "$0"
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echo "usage: $0 --i-understand [--channel 0|1]"
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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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if ! $CONFIRMED; then
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cat >&2 <<-'EOF'
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This script writes to a register of the memory controller's SMBus engine.
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It is written to be a no-op for the bus: the GO bit stays clear, so no
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SMBus transaction is issued, and the original register value is restored
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before the script exits. It is still a write to firmware-owned hardware.
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Re-run with --i-understand to proceed.
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EOF
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exit 2
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fi
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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=$REG_CH0_STAT ;;
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1) REG_DATA=$REG_CH1_DATA; REG_STAT=$REG_CH1_STAT ;;
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*) die "channel must be 0 or 1" ;;
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esac
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if ! command -v rdmsr >/dev/null; then
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echo "warning: rdmsr not found, the SMI question will stay unanswered." >&2
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echo " install msr-tools and 'modprobe msr' for the full result." >&2
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fi
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driver_is_loaded && die "unload i2c-imc-skylake first"
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BDF=$(find_pcu)
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echo "device: $BDF"
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echo "channel: $CHANNEL (DATA at $REG_DATA, STATUS at $REG_STAT)"
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echo
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original=$(read_reg "$BDF" "$REG_DATA")
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status=$(read_reg "$BDF" "$REG_STAT")
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echo "DATA before: $original"
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echo "STATUS before: $status"
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((original & GO_BIT)) && die "GO is set: a transaction is armed, refusing"
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((original & TSOD_ACTIVE_BIT)) &&
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die "TSOD_ACTIVE is set: firmware is using the engine, refusing"
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((status & STAT_BUSY)) && die "engine is BUSY, refusing"
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restore()
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{
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setpci -s "$BDF" "$REG_DATA.L=$(printf '%08x' "$original")" || true
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echo "DATA restored to $(read_reg "$BDF" "$REG_DATA")"
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}
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trap restore EXIT
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# Flip the low byte to something that is certainly different, GO still clear.
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probe=$(( (original & ~0xff) | ( ((original & 0xff) ^ 0x5a) & 0xff ) ))
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probe_hex=$(printf '0x%08x' "$probe")
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smi_before=$(read_smi_count)
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echo
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echo "writing $probe_hex through CF8/CFC (setpci)..."
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setpci -s "$BDF" "$REG_DATA.L=$(printf '%08x' "$probe")"
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readback=$(read_reg "$BDF" "$REG_DATA")
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smi_after=$(read_smi_count)
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echo "DATA after write: $readback"
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echo
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echo "=== result 1: did the write take effect? ==="
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if [[ "$readback" == "$probe_hex" ]]; then
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echo "STUCK - the CF8/CFC write reached the register."
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echo " The premise of the ECAM patch does not hold on this board;"
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echo " do not claim CF8/CFC writes are dropped."
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else
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echo "DROPPED - wrote $probe_hex, read back $readback."
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echo " Confirms that CF8/CFC writes to this function do not"
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echo " take effect on this board."
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fi
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echo
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echo "=== result 2: was an SMI raised? ==="
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if ((smi_before < 0 || smi_after < 0)); then
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echo "UNKNOWN - MSR_SMI_COUNT not readable (need msr-tools + modprobe msr)."
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else
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delta=$((smi_after - smi_before))
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echo "MSR_SMI_COUNT: $smi_before -> $smi_after (delta $delta)"
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if ((delta == 0)); then
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echo "NO SMI - the behaviour must not be attributed to SMM."
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else
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echo "SMI RAISED - System Management Mode is involved; say so, with"
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echo " this number, in the changelog."
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fi
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fi
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