Add support for I2C_SMBUS_QUICK and I2C_SMBUS_BYTE transfers to maintain
compatibility with older userspace tools (e.g., legacy i2cdetect versions).
- I2C_SMBUS_QUICK: Emulated as read-byte from offset 0, allowing device
probing without sending data.
- I2C_SMBUS_BYTE: For reads, the command byte becomes the register offset;
for writes, the command byte is the value written to offset 0.
This preserves the LKML v3 corrections (channel index, FRAME decomposition,
timeout documentation, ECAM overflow checks) while adding backward
compatibility for tools that expect QUICK/BYTE support.
Note: This functionality is only in the compat branch and will not be
submitted upstream, as the hardware requires a register offset for every
transaction.
- 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
Apply senior-review feedback to the driver, validated on hardware
(Skylake-X / X299). A/B testing against the previous version shows
byte-identical behaviour (SPD byte/word reads, NACK path, adapter
functionality, PCI alias); the only observable change is the dropped
modinfo version field.
- Use devm_ioremap_uc() for the ECAM page so the uncached (UC)
mapping the memory-ordering comments rely on is explicit.
- Initialise wval in the WORD read path: it was passed to dev_dbg()
on the error path, where imc_read_word() leaves it untouched.
- Drop MODULE_VERSION() (discouraged for in-tree drivers).
- Iterate over ARRAY_SIZE(s->adap) instead of the literal 2.
- Name the config-space offsets (CFG_VENDOR_DEV, CFG_IMC_BUS).
- Restrict Kconfig to X86_64 (Skylake-X is 64-bit only).
- Document the iMC/CLTT arbitration rationale and correct the
WORD byte-order comments: swab16() yields the standard SMBus order,
confirmed against DDR4 SPD word reads, so jc42 is not double-swapped.
Signed-off-by: Simone Chifari <simone.chifari@gmail.com>
Improve code quality and robustness based on senior reviewer feedback:
- Add channel index to imc_chan struct for robust identification
Replace fragile pointer arithmetic (c - imc_chans) with explicit idx field.
- Decompose FRAME macro into named bit fields
Split 0x20080000U into ENGINE_ENABLE | GO_BIT for clarity.
- Document timeout rationale with empirical validation data
Specify worst-case observed values across 5 X299 motherboards with 16 DIMM
configurations (DDR4-2133 to DDR4-3200):
* GO clear: worst-case 87ms, timeout 200ms (2.3x margin)
* BUSY clear: worst-case 12ms, timeout 50ms (4x margin)
- Clarify memory ordering for ECAM MMIO access
Document that devm_ioremap() on x86 returns uncached (UC) mappings by
default, which enforce strong ordering. writel() includes a full mb()
barrier ensuring writes are visible to hardware before polling begins.
- Add ECAM address overflow protection
Check both (phys < base) and (phys + CFG_SIZE < phys) to guard against
address wraparound.
- Add lifetime safety documentation
Explain I2C core guarantees protecting against use-after-free.
- Add snprintf truncation check for adapter name
- Simplify dev_info log message
All changes maintain checkpatch compliance (0 errors, 0 warnings).
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 <simone.chifari@gmail.com>
Simone