Re: [PATCH v12 2/6] mfd: add NXP MC33978/MC34978 core driver

[Lee Jones <lee@kernel.org>]

On Fri, 15 May 2026, Oleksij Rempel wrote:

> Add core Multi-Function Device (MFD) driver for the NXP MC33978 and
> MC34978 Multiple Switch Detection Interfaces (MSDI).
> 
> The MC33978/MC34978 devices provide 22 switch detection inputs, analog
> multiplexing (AMUX), and comprehensive hardware fault detection.
> 
> This core driver handles:
> - SPI communications via a custom regmap bus to support the device's
>   pipelined two-frame MISO response requirement.
> - Power sequencing for the VDDQ (logic) and VBATP (battery) regulators.
> - Interrupt demultiplexing, utilizing an irq_domain to provide 22 virtual
>   IRQs for switch state changes and 1 virtual IRQ for hardware faults.
> - Inline status harvesting from the SPI MSB to detect and trigger events
>   without requiring dedicated status register polling.
> 
> Child devices (pinctrl, hwmon, mux) are instantiated by the core driver
> from match data.
> 
> Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
> ---
> changes v12:
> - Split monolithic MFD driver into two modules per maintainer feedback:
>   * drivers/mfd/mc33978.c: Thin wrapper for SPI binding, power sequencing,
>     and child device registration
>   * drivers/platform/misc/mc33978-core.c: Complex core functionality
>     including custom regmap bus, IRQ domain, and event handling
> - Add mc33978_core_init() API exported by core module for MFD initialization
> - Introduce CONFIG_MC33978_CORE in drivers/platform/misc/Kconfig
> - Update CONFIG_MFD_MC33978 to select CONFIG_MC33978_CORE
> - Add MODULE_SOFTDEP("pre: mc33978-core") to ensure correct module load order
> - Rename struct mc33978_mfd_priv to context-specific names:
>   * mc33978_ddata in MFD driver
>   * mc33978_core_data in core module
> - Rename local variables from 'mc' to 'ddata'/'cdata' for clarity
> - Replace MC33978_DRV_NAME macro with string literal "mc33978"
> - Convert kerneldoc (/** */) on static functions to regular comments (/* */)
> - Adopt 100-character line limit throughout
> - Fix misleading cacheline alignment comment ("must be at end" -> "prevent
>   DMA corruption from adjacent fields")
> - Document IRQ locking strategy explicitly (irq_lock mutex for regmap/SPI,
>   irq_state_lock raw spinlock for atomic state access)
> - Reformat header file comments from inline style to preceding style for
>   improved readability
> - Enhance interrupt behavior documentation with detailed datasheet references
>   explaining INT_flg clear timing and FAULT_STAT latching behavior
> - add .suppress_bind_attrs = true
> changes v11:
> - Introduce synthetic wakeup bit to prevent hardware bit overloading and
>   avoid phantom transient faults.
> - Add smp_mb__before_atomic() to ensure memory visibility before
>   updating harvested_flags.
> - Update event processing to mask synthetic bits before evaluating
>   hardware fault conditions.
> - Introduce fault_lock spinlock to protect fault state members.
> - Replace manual memory barriers and READ_ONCE/WRITE_ONCE with
>   spinlock-protected access.
> - Introduce irq_state_lock raw spinlock to protect IRQ state fields.
> - Replace irq_lock mutex with raw spinlock in IRQ callbacks and event
>   handling paths.
> - Include MC33978_REG_ENTER_LPM in volatile and precious ranges.
> - Mark MC33978_REG_ENTER_LPM as readable to avoid regcache sync writes.
> changes v10:
> - Refactor IRQ setup into a common helper to unify the .map and .alloc
>   code paths.
> - Enable hierarchical IRQ support to allow integration with the
>   pinctrl/GPIO child domain.
> - Simplify event handling by removing redundant boolean return values
>   from internal handlers.
> - Fix IRQ cleanup by disposing of all active mappings before removing
>   the IRQ domain.
> - Standardize IRQ constants using MC33978_NUM_IRQS for consistent domain
>   sizing and bounds checks.
> changes v9:
> - Fix null irq_domain dereference from debugfs race by initializing IRQ domain
>   early before regmap initialization.
> - Refactor mc33978_handle_fault_condition() to improve readability by keeping
>   variable declarations at the top and adding inline comments.
> - Fix spurious transient fault events caused by redundant STAT_FAULT flags
>   during event loop.
> - Fix spurious interrupt loops by explicitly returning -ENODATA in
>   mc33978_rx_decode() for registers without status bits.
> - Validate hwirq bounds in mc33978_irq_domain_alloc() to prevent corruption
>   of irq_rise/irq_fall bitmasks by malformed device tree inputs.
> - set DOMAIN_BUS_NEXUS
> - Protect work on teardown
> - remove IRQF_SHARED
> changes v8:
> - Fix TOCTOU race condition in SPI event harvesting loop by grabbing
>   harvested_flags before hardware reads.
> - Fix broken hierarchical IRQ allocation by replacing
>   irq_domain_set_hwirq_and_chip() with irq_domain_set_info() and passing
>   the handle_simple_irq flow handler.
> - Fix out-of-bounds stack read and endianness bug in for_each_set_bit() by
>   typing fired_pins as unsigned long instead of casting u32.
> - Prevent DMA cacheline corruption by explicitly aligning rx_frame with
>   ____cacheline_aligned to separate it from tx_frame.
> - Prevent spurious IRQs by verifying irq_find_mapping() returns non-zero
>   before calling handle_nested_irq().
> - Prevent missed transient hardware faults by explicitly evaluating
>   hw_flags in mc33978_handle_fault_condition().
> - Fix missing memory barrier in mc33978_harvest_status() with
>   smp_mb__after_atomic() to ensure harvested_flags visibility.
> - Fix devres use-after-free teardown race by using INIT_WORK and a custom
>   cancel action after the IRQ domain is destroyed, instead of
>   devm_work_autocancel.
> - Prevent spurious pin interrupts on boot by priming cached_pin_state via
>   a regmap_read() during probe before enabling IRQs.
> - Implement .irq_set_wake callback to support system wake from
>   hardware faults and switch state changes.
> changes v7:
> - Fix event handling race condition with smp_mb()
> - Replace INIT_WORK() with devm_work_autocancel()
> changes v6:
> - Remove the hardcoded bypass in irq_set_type to allow child drivers to
>   configure the FAULT line for edge-triggering.
> - Implement software edge-detection for FAULT interrupt.
> - Add MC33978_FAULT_ALARM_MASK to the shared header for child devices
> - Use READ_ONCE() and WRITE_ONCE() for lockless shared state variables
>   (cached_pin_mask, irq_rise, irq_fall, bus_fault_active,
>   cached_fault_active) accessed across the SPI harvesting context and
>   the event worker.
> - Add an if (hwirq < MC33978_NUM_PINS) guard in irq_mask() and
>   irq_unmask() to prevent the FAULT hwirq (22) from altering the
>   physical pin mask registers.
> - Lowercase the error strings in dev_err_probe()
> - Add inline comments explaining the irq_map fallback behavior
> changes v5:
> - no changes
> changes v4:
> - Removed .of_compatible strings from the mfd_cell arrays
> changes v3:
> - Select IRQ_DOMAIN_HIERARCHY in Kconfig
> - Add .alloc and .free callbacks to irq_domain_ops to support hierarchical
>   IRQ domains
> - Set IRQ_DOMAIN_FLAG_HIERARCHY flag on the core MFD irq_domain
> - replace manual lock/unlock with guard()
> changes v2:
> - Rewrite the driver header comment
> - Explicitly reject IRQ_TYPE_LEVEL_HIGH and IRQ_TYPE_LEVEL_LOW in
>   mc33978_irq_set_type() to correctly reflect the hardware's edge-only
>   interrupt capabilities.
> - Pass the hardware fault IRQ to the hwmon child driver via mfd_cell
>   resources, rather than requiring the child to parse the parent's irq_domain.
> - Ensure the Kconfig strictly depends on OF and SPI
> ---
>  drivers/mfd/Kconfig                  |   15 +
>  drivers/mfd/Makefile                 |    2 +
>  drivers/mfd/mc33978.c                |  187 +++++
>  include/linux/mfd/mc33978.h          |  160 ++++

This is one patch.

>  drivers/platform/Kconfig             |    2 +
>  drivers/platform/Makefile            |    1 +
>  drivers/platform/misc/Kconfig        |   10 +
>  drivers/platform/misc/Makefile       |    6 +
>  drivers/platform/misc/mc33978-core.c | 1106 ++++++++++++++++++++++++++

This should be in another.

>  9 files changed, 1489 insertions(+)
>  create mode 100644 drivers/mfd/mc33978.c
>  create mode 100644 drivers/platform/misc/Kconfig
>  create mode 100644 drivers/platform/misc/Makefile
>  create mode 100644 drivers/platform/misc/mc33978-core.c
>  create mode 100644 include/linux/mfd/mc33978.h

-- 
Lee Jones