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@nxp.com>
---
Changes in v5:
- add npins to pinctrl_generic_to_map()
- remove pins = kmalloc() in pinctrl_generic_to_map().
- Link to v4: https://lore.kernel.org/r/20260325-pinctrl-mux-v4-0-043c2c82e623@nxp.com
Changes in v4:
- use Conor Dooley suggest to extract funciton pinctrl_generic_pins_to_map()
- Link to v3: https://lore.kernel.org/r/20260311-pinctrl-mux-v3-0-236b1c17bf9b@nxp.com
Changes in v3:
- collect rob's review tag for binding
- extend and use pinctrl_generic_pins_function_dt_node_to_map()
- add judgement about
commit 2243a87d90b42eb38bc281957df3e57c712b5e56
"pinctrl: avoid duplicated calling enable_pinmux_setting for a pin"
which call pinmux_disable_setting() before pinmux_enable_setting() when
switch state. It is actually what wanted. Previous remove .disable() to
avoid hardware glitch when switch state.
New .release_mux() call intent just release software resource, like lock,
don't touch hardware register. No glitch involve. Comments already added
Linus Walleij:
I hope this answer all of your questions. If I missed, let me know
- Link to v2: https://lore.kernel.org/r/20260225-pinctrl-mux-v2-0-1436a25fa454@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 (7):
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: extract pinctrl_generic_to_map() from pinctrl_generic_pins_function_dt_node_to_map()
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/pinconf.h | 18 ++
drivers/pinctrl/pinctrl-generic-mux.c | 197 +++++++++++++++++++++
drivers/pinctrl/pinctrl-generic.c | 94 ++++++----
drivers/pinctrl/pinmux.c | 5 +
include/linux/mux/consumer.h | 16 +-
include/linux/pinctrl/pinmux.h | 5 +
14 files changed, 424 insertions(+), 62 deletions(-)
---
base-commit: ff76d257e86235eb07ef33db8644a517c48d1c3f
change-id: 20260213-pinctrl-mux-df9c5b661540
Best regards,
--
Frank Li <Frank.Li@nxp.com>