Add support for the Monolithic Power Systems MPQ8646 step-down
converter as a PMBus device.

  1/3 pmbus core: add and export pmbus_get_hwmon_device() so a chip
      driver can call hwmon_notify_event() from an in-driver
      alarm-poll fallback (lm90-style) on boards where the chip's
      SMBALERT# pin is unavailable to the CPU.
  2/3 dt-bindings: the MPQ8646 binding; schema inspired from the
      mpq8785 (same mps,vout-fb-divider-ratio-permille property).
  3/3 the MPQ8646 driver: PMBus telemetry plus MFR_CFG_EXT
      gate-close retry after CLEAR_LAST_FAULT, alarm acknowledge via
      inX_reset_history, MPS-extended STATUS_WORD decode and
      post-mortem clear, the alarm-poll fallback for boards without
      SMBALERT, and on_off_config / vout_margin / mfr_pmbus_lock
      sysfs.

Signed-off-by: Vincent Jardin <vjardin@free.fr>
---
Changes in v3 (all reported by the Sashiko AI review on v2):
- driver: alarm_poll_interval_ms is now a debugfs fops
- driver: pmbus_lock() around the async raw i2c accesses: the poll
  worker and the CLEAR_LAST_FAULT force sequence, the nvmem snapshot read
  keeps mps_lock (read-only, no chip-state change)
- driver: update last_probe_rc/last_probe_data under mps_lock to avoid
  torn diagnostics
- driver: remove the dead PMBUS_PAGE swallow in write_byte
- driver: remove the probe_page_write debugfs hook
- Link to v2: https://lore.kernel.org/r/20260723-mpq8646_v0-v2-0-3c4cb71f23c0@free.fr

Changes in v2:
- driver: register debugfs only after the DT-property validation, to
  avoid an early probe error to avoid dangling debugfs entries
- driver: do not schedule the alarm-poll worker when SMBALERT# (irq)
  is wired, and do not re-arm it from the worker in that case
- driver: dput() the dentry returned by debugfs_lookup()
- driver: hold mps_lock around the nvmem snapshot reads
- driver: fix VID coefficients comment
- dt-bindings: fix typo of the commit message
- Link to v1: https://lore.kernel.org/r/20260723-mpq8646_v0-v1-0-14363c75916f@free.fr

---
Vincent Jardin (3):
      hwmon: pmbus: event notification with alarms
      dt-bindings: hwmon: pmbus: add MPS MPQ8646 binding
      hwmon: pmbus: add MPQ8646 driver

 .../bindings/hwmon/pmbus/mps,mpq8646.yaml          |   50 +
 Documentation/hwmon/mpq8646.rst                    |  314 +++++
 MAINTAINERS                                        |    8 +
 drivers/hwmon/pmbus/Kconfig                        |   11 +
 drivers/hwmon/pmbus/Makefile                       |    1 +
 drivers/hwmon/pmbus/mpq8646.c                      | 1237 ++++++++++++++++++++
 drivers/hwmon/pmbus/pmbus.h                        |    1 +
 drivers/hwmon/pmbus/pmbus_core.c                   |    8 +
 8 files changed, 1630 insertions(+)
---
base-commit: 248951ddc14de84de3910f9b13f51491a8cd91df
change-id: 20260723-mpq8646_v0-3383cb574d7a

Best regards,
-- 
Vincent Jardin <vjardin@free.fr>