[PATCH v8 0/5] Add support for AAEON SRG-IMX8P MCU

This patch series introduces support for the AAEON SRG-IMX8P embedded
controller (MCU). The MCU is connected via I2C and provides GPIO and
watchdog functionality for the SRG-IMX8P board.

The series includes:
- Device tree binding for the MFD driver
- MFD driver that serves as the core driver for the MCU
- GPIO driver implementing the GPIO functionality
- Watchdog driver for system monitoring
- MAINTAINERS entry for the new drivers

The drivers follow the standard Linux kernel subsystem patterns, with
the MFD driver registering the sub-devices (GPIO and watchdog) which
are then handled by their respective subsystem drivers.

Signed-off-by: Thomas Perrot (Schneider Electric) <[email protected]>
---
Changes in v8:
- mfd: add .use_single_read = true to regmap config; the MCU produces exactly
  one response byte per command and a bulk read passing val_size > 1 to the
  bus callback would be incorrect
- watchdog: call watchdog_stop_ping_on_suspend() in probe so the kthread ping
  worker is cancelled before platform devices are suspended, preventing I2C
  transfers on a suspended bus
- watchdog: check watchdog_hw_running() alongside watchdog_active() in the
  suspend/resume callbacks so watchdog is stopped before sleep and restarted
  on wake, preventing a spurious MCU reset if suspend exceeds the 25-second
  hardware timeout
- Link to v7: https://lore.kernel.org/r/[email protected]

Changes in v7:
- mfd: fix select REGMAP Kconfig entry indented with spaces instead of a tab
- mfd: use devm_kcalloc() instead of devm_kzalloc() for the cmd buffer allocation
- mfd: add .use_single_write = true to the regmap config to prevent regcache sync
or debugfs from issuing multi-register writes that would overflow the fixed 3-byte
cmd buffer
- watchdog: remove max_timeout; it is documented as irrelevant when
max_hw_heartbeat_ms is set and is silently ignored by the watchdog core
- watchdog: pass dev->parent to watchdog_init_timeout() so that the timeout-sec
DT property is correctly read from the MCU I2C node; the MFD child platform device
has no of_node of its own
- watchdog: add suspend/resume PM hooks to stop the watchdog before entering sleep
and restart it on resume, preventing spurious resets if suspend lasts longer than
the 25-second hardware heartbeat
- Link to v6: https://lore.kernel.org/r/[email protected]

Changes in v6:
- mfd: rename local variable to ddata in probe
- mfd: fix driver name from "aaeon_mcu" to "aaeon-mcu"
- mfd: set I2C_M_DMA_SAFE on all i2c_msg flags so the host driver
  skips bounce-buffering the heap-allocated DMA-safe buffers
- mfd: drop COMPILE_TEST
- gpio: replace __set/__clear/__assign_bit with atomic set_bit/
  clear_bit/assign_bit to fix potential races on shared bitmaps
- gpio: write output value before switching pin to output mode to
  avoid a potential glitch on direction_output
- gpio: add MODULE_ALIAS("platform:aaeon-mcu-gpio")
- watchdog: add WDIOF_SETTIMEOUT and watchdog_init_timeout() so the
  software timeout is configurable via ioctl, DT timeout-sec or
  the watchdog_timeout boot parameter
- watchdog: add watchdog_stop_on_reboot() to prevent a spurious
  reset from the external MCU during system shutdown
- watchdog: add MODULE_ALIAS("platform:aaeon-mcu-wdt")
- Link to v5: https://lore.kernel.org/r/[email protected]

Changes in v5:
- mfd: use heap-allocated DMA-safe buffers for I2C transfers, replacing
  stack-allocated buffers in the regmap bus callbacks
- mfd: switch from REGCACHE_NONE to REGCACHE_MAPLE; add volatile_reg
  callback marking GPIO input read registers (opcode 0x72) as volatile;
  add max_register
- mfd: use PLATFORM_DEVID_AUTO instead of PLATFORM_DEVID_NONE
- mfd: use MFD_CELL_BASIC() macro for cell definitions
- mfd: use dev_err_probe() for regmap initialization error
- Link to v4: https://lore.kernel.org/r/[email protected]

Changes in v4:
- mfd: switch to a custom regmap bus; remove aaeon_mcu_i2c_xfer() and the aaeon_mcu_dev struct
- mfd: locking delegated to regmap's built-in mutex; drop explicit mutex
- mfd: remove firmware version reading at probe time
- gpio, watchdog: use regmap_read()/regmap_write() via dev_get_regmap()
- include: replace aaeon_mcu_i2c_xfer() declaration with AAEON_MCU_REG() macro
- dt-bindings: remove unused label from example node
- Link to v3: https://lore.kernel.org/r/[email protected]

Changes in v3:
- Renamed SRG-IMX8PL to SRG-IMX8P
- dt-bindings: add gpio-controller properties as required
- mfd: move struct aaeon_mcu_dev from header to .c file (private)
- mfd: use guard(mutex) and devm_mutex_init() for cleanup
- mfd: firmware version log changed to dev_dbg()
- mfd: add select MFD_CORE to Kconfig
- Kconfig: add || COMPILE_TEST to all three drivers
- watchdog: add comments explaining hardware timeout and WDOG_HW_RUNNING
- watchdog: remove unused platform_set_drvdata()
- watchdog: add a function to query the status
- Link to v2: https://lore.kernel.org/r/[email protected]

Changes in v2:
- Fold GPIO and watchdog bindings into MFD binding
- Drop OF_GPIO dependency in GPIO Kconfig
- Use __set_bit/__clear_bit/__assign_bit instead of atomic variants
- Various driver cleanups and improvements
- Link to v1: https://lore.kernel.org/r/[email protected]

---
Thomas Perrot (Schneider Electric) (5):
      dt-bindings: vendor-prefixes: Add AAEON vendor prefix
      dt-bindings: mfd: Add AAEON embedded controller
      mfd: aaeon: Add SRG-IMX8P MCU driver
      gpio: aaeon: Add GPIO driver for SRG-IMX8P MCU
      watchdog: aaeon: Add watchdog driver for SRG-IMX8P MCU

 .../bindings/mfd/aaeon,srg-imx8p-mcu.yaml          |  67 ++++++
 .../devicetree/bindings/vendor-prefixes.yaml       |   2 +
 MAINTAINERS                                        |  10 +
 drivers/gpio/Kconfig                               |   9 +
 drivers/gpio/Makefile                              |   1 +
 drivers/gpio/gpio-aaeon-mcu.c                      | 230 +++++++++++++++++++++
 drivers/mfd/Kconfig                                |  11 +
 drivers/mfd/Makefile                               |   1 +
 drivers/mfd/aaeon-mcu.c                            | 207 +++++++++++++++++++
 drivers/watchdog/Kconfig                           |  10 +
 drivers/watchdog/Makefile                          |   1 +
 drivers/watchdog/aaeon_mcu_wdt.c                   | 168 +++++++++++++++
 include/linux/mfd/aaeon-mcu.h                      |  40 ++++
 13 files changed, 757 insertions(+)
---
base-commit: d358e5254674b70f34c847715ca509e46eb81e6f
change-id: 20251211-dev-b4-aaeon-mcu-driver-e0e89ebf4afb

Best regards,
-- 
Thomas Perrot (Schneider Electric) <[email protected]>