dpll: add NCO pin type and zl3073x support

Add a new DPLL_PIN_TYPE_INT_NCO pin type for virtual pins representing
the NCO mode of a DPLL and implement support for it in the zl3073x driver.

Patch 1 adds a STATE_CONNECTED_OVERRIDE pin capability for pins that
can override input selection in any DPLL mode, with a WARN_ON check
in dpll_pin_register() that STATE_CAN_CHANGE is also set.

Patch 2 adds the new INT_NCO pin type to the DPLL netlink spec and
UAPI header.

Patch 3 replaces the single 2s poll timeout with per-operation timeouts
based on Microchip proprietary source code and own measurement.

Patch 4 adds a per-DPLL serialization mutex taken by all DPLL callbacks
and the periodic worker, establishing a single lock that protects all
per-channel state. The chan_state_update() call is moved under this lock.

Patch 5 adds a virtual NCO input pin to the zl3073x driver that allows
userspace to switch a DPLL channel into NCO mode. The pin reports
connected/active state when the channel is in NCO mode and handles
the hardware-specific details of mode transitions including automatic
df_offset capture and 1PPS phase preservation.

Link: https://lore.kernel.org/netdev/20260531194423.383366-1-iv...

Changes:
v6:
  - New patch 1: STATE_CONNECTED_OVERRIDE pin capability with
    WARN_ON validation in dpll_pin_register() and documentation
    in dpll.rst Pin selection section.
  - Use READ_ONCE/WRITE_ONCE for per-device freq_monitor and
    phase_avg_factor accessed from periodic worker without lock.
    Remove unnecessary zldpll->lock from phase_offset_avg_factor
    get/set callbacks (patch 4).
  - Configure dpll_df_read register (ref_ofst=0, cmd=ACC_I) before
    NCO mode switch with 25ms delays for internal register update
    (reported by Chris du Quesnay, Microchip) (patch 5).
  - Mark df_offset as unknown at probe when firmware left channel
    in NCO mode (patch 5).
  - See individual patches for detailed changelogs.
v5:
  - Rebased on net-next after the freq_monitor per-device fix
    landed via net.
  - Move phase_offset_avg_factor_set notification loop outside lock
    to avoid lockdep false positive on multi-channel devices (patch 4).
  - See individual patches for detailed changelogs.
v4:
  - New patch 3: per-operation poll timeouts
  - New patch 4: per-DPLL serialization lock
  - See individual patches for detailed changelogs.
v3:
  - fixed SoB position
v2:
  - See individual patches for detailed changelogs.

Ivan Vecera (5):
  dpll: add STATE_CONNECTED_OVERRIDE pin capability
  dpll: add DPLL_PIN_TYPE_INT_NCO pin type
  dpll: zl3073x: use per-operation poll timeouts
  dpll: zl3073x: add per-DPLL serialization lock
  dpll: zl3073x: add NCO virtual input pin

 Documentation/driver-api/dpll.rst     |   7 +
 Documentation/netlink/specs/dpll.yaml |  19 +
 drivers/dpll/dpll_core.c              |   6 +-
 drivers/dpll/dpll_nl.c                |   2 +-
 drivers/dpll/zl3073x/chan.c           | 128 ++++++-
 drivers/dpll/zl3073x/chan.h           |  48 +++
 drivers/dpll/zl3073x/core.c           |  48 +--
 drivers/dpll/zl3073x/core.h           |  12 +-
 drivers/dpll/zl3073x/dpll.c           | 489 ++++++++++++++++++++++----
 drivers/dpll/zl3073x/dpll.h           |   4 +
 drivers/dpll/zl3073x/regs.h           |  11 +
 include/uapi/linux/dpll.h             |   8 +
 12 files changed, 677 insertions(+), 105 deletions(-)


base-commit: cef9d6804030793cf8b8796fd6936197d065dd3e
-- 
2.53.0