[PATCH v3 0/3] counter: add GPIO-based quadrature encoder driver

[Wadim Mueller]

This series adds a new counter subsystem driver that implements
quadrature encoder position tracking using plain GPIO pins with
edge-triggered interrupts.

The driver is intended for low to medium speed rotary encoders where
hardware counter peripherals (eQEP, FTM, etc.) are unavailable or
already in use. It targets the same use-cases as interrupt-cnt.c but
provides full quadrature decoding instead of simple pulse counting.

Features:
  - X1, X2, X4 quadrature decoding and pulse-direction mode
  - Optional index signal for zero-reset
  - Configurable ceiling (position clamping)
  - Standard counter subsystem sysfs + chrdev interface
  - Enable/disable via sysfs with IRQ gating

Tested on TI AM64x (Cortex-A53) with a motor-driven rotary encoder
at up to 2 kHz quadrature edge rate.

Changes in v3:
  - Pick up Acked-by: Conor Dooley on the DT binding patch.
  - No code changes.

Changes in v2:
  - DT binding: rephrase description to describe hardware, not
    driver/sysfs behaviour (Conor Dooley)
  - DT binding: drop redundant example without index GPIO (Conor Dooley)

Wadim Mueller (3):
  dt-bindings: counter: add gpio-quadrature-encoder binding
  counter: add GPIO-based quadrature encoder driver
  MAINTAINERS: add entry for GPIO quadrature encoder counter driver

 .../counter/gpio-quadrature-encoder.yaml      |  60 ++
 MAINTAINERS                                   |   7 +
 drivers/counter/Kconfig                       |  15 +
 drivers/counter/Makefile                      |   1 +
 drivers/counter/gpio-quadrature-encoder.c     | 710 ++++++++++++++++++
 5 files changed, 793 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/counter/gpio-quadrature-encoder.yaml
 create mode 100644 drivers/counter/gpio-quadrature-encoder.c

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2.52.0