hwmon: (pmbus/ltc2978) Add support for LT7175, LT7176P, LTM4681, LTM4682

[cdeguzm4]

PR Description

Adds support for the following chips to the existing ltc2978 PMBus driver:

• LT7175 / LT7175-1 (part of LT7170 family, MFR_SPECIAL_ID 0x1C1D masked to 0x1C10)
• LT7176P / LT7176P-1 (same family, same MFR_SPECIAL_ID)
• LTM4681 — quad 31.25A / single 125A µModule step-down regulator (commits inherited from reviewed PR Dev/ltm4681 add LTM4681 and LTM4682 #3085, now owned by this PR)
• LTM4682 — same architecture as LTM4681 (commits inherited from reviewed PR Dev/ltm4681 add LTM4681 and LTM4682 #3085, now owned by this PR)

Changes include:

• DT bindings YAML updates (Documentation/devicetree/bindings/hwmon/lltc,ltc2978.yaml)
• Driver code additions in drivers/hwmon/pmbus/ltc2978.c (chip IDs, ltc2978_get_id() string matches, probe switch cases, i2c_id/of_match tables)
• Driver documentation updates (Documentation/hwmon/ltc2978.rst)
• Kconfig help text update

PR Type

• Bug fix (a change that fixes an issue)
• New feature (a change that adds new functionality)
• Breaking change (a change that affects other repos or cause CIs to fail)

PR Checklist

• I have conducted a self-review of my own code changes
• I have compiled my changes, including the documentation
• I have tested the changes on the relevant hardware
• I have updated the documentation outside this repo accordingly
• I have provided links for the relevant upstream lore

[github-actions]

LLM review

This series adds support for the LTM4681/LTM4682 µModule regulators and the
LT7175/LT7176P buck regulators to the hwmon/pmbus/ltc2978 driver, along with
the corresponding dt-bindings and documentation updates.

Session: 38230823284

1f8f28d672c5 - Add support for LTM4681 and LTM4682

Wrong MFR_SPECIAL_ID for LTM4681: LTM4681_ID is defined as 0x4140,
identical to LTM4680_ID. The LTM4681 datasheet (now available in the
corpus) documents MFR_SPECIAL_ID as 0x415X, which masks to 0x4150 with
LTC2978_ID_MASK (0xfff0), not 0x4140. LTM4680_ID (0x414X) and
LTM4682_ID (0x418X → 0x4180) are correctly defined per their own
datasheets. As written, ltc2978_get_id() can never distinguish LTM4681 from
LTM4680 over the primary MFR_SPECIAL_ID path - it always resolves to
ltm4680.

Missing switch case: separately, ltm4681 is added to enum chips, the
i2c_device_id/of_device_id tables, and the MFR_MODEL ASCII fallback
table, but ltc2978_probe() has no case ltm4681:. Even if the ID value
above is fixed and ltc2978_get_id() correctly returns ltm4681, probe()
falls through to default: return -ENODEV; because pmbus_driver_info is
never populated for it.

Incorrect comment: /* Undocumented on LTM4682 */ was added next to
LTC3880_MFR_TEMPERATURE2_PEAK (0xf4), but both the LTM4681 and LTM4682
datasheets explicitly document MFR_TEMPERATURE_2_PEAK at 0xF4. The
comment also introduces the checkpatch "space before tabs" warning.

Also a Kconfig typo ("TM4686" instead of "LTM4686") and broken
indentation (spaces instead of tabs) in Documentation/hwmon/ltc2978.rst.

536bd674d45a - Add support for LT7175 and LT7176P

The 0x1C1D → 0x1C10 MFR_SPECIAL_ID masking claim in the commit message
is confirmed against both the LT7170/LT7170-1 and LT7176/LT7176-1
datasheets (both report 0x1C1D). However, no datasheet for "LT7175" or
"LT7176P" exists in the available corpus; only "LT7176/LT7176-1" (no "P") is
documented, with IC_DEVICE_ID string "LT7176 or LT7176-1" (no trailing
P). The new code matches "LT7176P"/"LT7176P-1" against
PMBUS_IC_DEVICE_ID - if actual silicon reports "LT7176", this match never
succeeds. Could not confirm or deny this is a real product variant; worth
double-checking against real silicon.

The Kconfig help text for SENSORS_LTC2978_REGULATOR was not updated to
mention LT7175/LT7176P.

CI warnings

checkpatch flagged (non-strict, didn't fail the job):

• Two commit descriptions (27076a97a764, 1f8f28d672c5) exceed 75
  chars/line.
• drivers/hwmon/pmbus/ltc2978.c:52: space before tab in the
  LTC3880_MFR_TEMPERATURE2_PEAK definition (1f8f28d672c5).

Verification data

Datasheets were pulled from the docling-converted corpus: ltm4680.md,
ltm4681.md, ltm4682.md, lt7170-lt7170-1.md, lt7176_lt7176-1.md. A
corpus-wide search confirmed no LT7175/LT7176P datasheet is present.
ltm4681.md's MFR_SPECIAL_ID entry (0x415X) and MFR_TEMPERATURE_2_PEAK
entry (0xF4) were used for the findings above. dt-doc-validate was run
against the updated binding with no errors. The driver was rebuilt with
set_arch gcc_x86 + get_adi_ci_defconfig + auto_set_kconfig (enables
CONFIG_SENSORS_LTC2978), confirming it compiles cleanly both before and
after the suggested fixups.

Suggested patches

• 0001-fixup-hwmon-pmbus-ltc2978-Add-support-for-LTM4681-an.patch
  (1f8f28d672c5) — fixes LTM4681_ID, adds the missing case ltm4681:,
  removes the incorrect "Undocumented on LTM4682" comment (also fixes the
  space-before-tab warning), and fixes the rst indentation.
• 0002-fixup-hwmon-pmbus-ltc2978-Add-support-for-LT7175-and.patch
  (536bd674d45a) — fixes the Kconfig "TM4686" typo and adds LT7175/LT7176P
  to the SENSORS_LTC2978_REGULATOR help text.

Apply with:

cd path/to/repository
export GITHUB_TOKEN=ghp_***
apply-patches --repo=analogdevicesinc/linux 38230823284

Install instructions

The following one-liner installs the script if not present already:

curl -fSsL "https://raw.githubusercontent.com/analogdevicesinc/doctools/refs/heads/main/ci/scripts/apply-patches.sh"      -o ~/.local/bin/apply-patches.sh &&   grep -q "/apply-patches.sh" ~/.bashrc || echo "source ~/.local/bin/apply-patches.sh" >> $_ ; . $_

More information at AI Usage.

[gastmaier]

llm findings seem correct.