Posted 2026-07-28:
https://lore.kernel.org/linux-i2c/[email protected]/
The badge tracks the new thread, and the local Claude Code settings
directory joins the gitignore: it holds machine-local permissions and
must never reach the public mirror.
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.
- Rewrite timeout comments with single-board test data (drop
multi-board validation claim not backed by the test campaign)
- Reword CLTT arbitration comment as verified observation, drop TODO
- Drop CONFIG_ACPI fallback stub; Kconfig already depends on ACPI
- Quiet probe: demote informational messages to dev_dbg()
- Kconfig: allow COMPILE_TEST builds
- Cover letter: v3 subject prefix, complete changes-since-v2 list,
updated diffstat, drop stray Signed-off-by, fix GO-bit wording
- Ignore local reviewer Q&A notes
The engine exposes only SMBus BYTE_DATA/WORD_DATA, so i2cdetect (which
needs SMBus QUICK or READ_BYTE) cannot scan the bus. Replace the
misleading "i2cdetect -r/-y" scan instructions with a direct i2cget
byte-data read in the README, the cover letter and the smoke test.
Also gitignore the archived internal working documents
(docs/archive-*.md).
Signed-off-by: Simone Chifari <[email protected]>
Add a driver for the integrated memory controller (iMC) SMBus engine on
Intel Skylake-X / Cascade Lake-X processors (socket LGA 2066, platform
X299, PCU function 8086:2085).
The engine provides two SMBus channels — one per pair of DIMM slots —
over which SPD EEPROMs, DDR4 thermal sensors and third-party LED
controllers are accessible. Exposing it as a pair of standard Linux I2C
adapters lets existing tools (i2c-tools, lm-sensors) use it without
bespoke sysfs hacks.
Key design decisions:
- ECAM MMIO access instead of CF8/CFC port I/O (SMM traps port writes)
- Dynamic MCFG table parsing for mmcfg_base (no hardcoding)
- Support for SMBus BYTE_DATA and WORD_DATA transfers
- devm-managed resources with automatic cleanup
- Global mutex to serialize transactions across both channels sharing
the same ECAM mapping
Signed-off-by: Simone Chifari <[email protected]>
Simone