v2 said firmware filters CF8/CFC config writes to this function and that
the registers are reachable only through ECAM. That was never tested; the
only evidence was the boot line "PCI: Using configuration type 1", which
names the accessor and says nothing about a write failing.
Measured on the board, driver unloaded:
# setpci -s 16:1e.5 9c.L=20085002 # read SPD 0x50 register 0x02
# setpci -s 16:1e.5 9c.L
20005002 # GO consumed by the engine
# setpci -s 16:1e.5 a8.L
0000500c # READ_DONE, no error
# setpci -s 16:1e.5 b4.L
0000000c # SPD byte 2, DDR4 type code
The command executes and returns correct data through the ordinary
accessors, and MSR_SMI_COUNT does not move across it. So the driver now
uses pci_read_config_dword() and pci_write_config_dword(), the submission
is a single patch again, and nothing in it touches the PCI core. The
cover letter retracts the claim explicitly rather than dropping it
quietly, because v2 was posted with it.
Correctness work in the same pass:
- the completion bits are latched, so a command word that never reaches
the register is indistinguishable from a completed transfer and the
caller gets the previous transaction's data. Read the command word
back and require it to be the one just written; the engine only ever
clears GO, which the measurement above shows directly;
- 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.
An earlier version of the latched-DONE check required the GO bit to be
seen set or the status word to change. That was wrong: repeated transfers
with the same outcome leave STATUS bit for bit identical, and GO is
consumed faster than a config read-back can observe it. It produced false
positives on 3 of 15 smoke-test items before being replaced.
Add Documentation/i2c/busses/i2c-imc-skylake.rst, which every other PC
SMBus driver has and which was asked for on the 2020 iMC thread, and the
tools/ scripts for the hardware measurements: probe-cf8-write.sh and
probe-cf8-transaction.sh produced the result above, dump-pcu-config.sh is
the search for a TSOD polling control, watch-engine.sh is the firmware
activity measurement.
Smoke test on the X299 system with the current module: 15 checks, 0
failures, dmesg clean.
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.
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