[PATCH v2 0/6] pinctrl: Add generic pinctrl for board-level mux chips

[Frank Li]

Add a generic pinctrl binding for board-level pinmux chips that are
controlled through the multiplexer subsystem.

On some boards, especially development boards, external mux chips are used
to switch SoC signals between different peripherals (e.g. MMC and UART).
The mux select lines are often driven by a GPIO expander over I2C,
as illustrated below:

        ┌──────┐      ┌─────┐
        │ SOC  │      │     │    ┌───────┐
        │      │      │     │───►│ MMC   │
        │      │      │ MUX │    └───────┘
        │      ├─────►│     │    ┌───────┐
        │      │      │     │───►│ UART  │
        │      │      └─────┘    └───────┘
        │      │         ▲
        │      │    ┌────┴──────────────┐
        │ I2C  ├───►│ GPIO Expander     │
        └──────┘    └───────────────────┘

Traditionally, gpio-hog is used to configure the onboard mux at boot.
However, the GPIO expander may probe later than consumer devices such as
MMC. As a result, the MUX might not be configured when the peripheral
driver probes, leading to initialization failures or data transfer errors.

Introduce a generic pinctrl binding that models the board-level MUX as a
pin control provider and builds proper device links between the MUX, its
GPIO controller, and peripheral devices. This ensures correct probe
ordering and reliable mux configuration.

The implementation leverages the standard multiplexer subsystem, which
provides broad support for onboard mux controllers and avoids the need for
per-driver custom MUX handling

Signed-off-by: Frank Li <Frank.Li at nxp.com>
---
Changes in v2:
- Add release_mux callback,
  test insmod/rmmod, mux_state_(de)select() called.
- Link to v1: https://lore.kernel.org/r/20260219-pinctrl-mux-v1-0-678d21637788@nxp.com

---
Frank Li (6):
      mux: add devm_mux_control_get_from_np() to get mux from child node
      dt-bindings: pinctrl: Add generic pinctrl for board-level mux chips
      pinctrl: add optional .release_mux() callback
      pinctrl: add generic board-level pinctrl driver using mux framework
      arm64: dts: imx8mp-evk: add board-level mux for CAN2 and MICFIL
      arm64: dts: imx8mp-evk: add flexcan2 overlay file

 .../bindings/pinctrl/pinctrl-multiplexer.yaml      |  57 +++++
 .../devicetree/bindings/pinctrl/pinctrl.yaml       |   2 +-
 arch/arm64/boot/dts/freescale/Makefile             |   4 +
 .../boot/dts/freescale/imx8mp-evk-flexcan2.dtso    |  15 ++
 arch/arm64/boot/dts/freescale/imx8mp-evk.dts       |  23 +-
 drivers/mux/core.c                                 |  40 ++--
 drivers/pinctrl/Kconfig                            |   9 +
 drivers/pinctrl/Makefile                           |   1 +
 drivers/pinctrl/pinctrl-generic-mux.c              | 241 +++++++++++++++++++++
 drivers/pinctrl/pinmux.c                           |   5 +
 include/linux/mux/consumer.h                       |  16 +-
 include/linux/pinctrl/pinmux.h                     |   5 +
 12 files changed, 395 insertions(+), 23 deletions(-)
---
base-commit: ff76d257e86235eb07ef33db8644a517c48d1c3f
change-id: 20260213-pinctrl-mux-df9c5b661540

Best regards,
--
Frank Li <Frank.Li at nxp.com>