[PATCH v9 0/6] Add VIM4 MCU/FAN support

The Khadas VIM4 board features a different MCU variant compared to
previous VIM boards.
While it shares the same I2C-based communication model,
it differs in some ways:

  - A distinct register map with its own volatile/writeable register set
  - A fan control with 0–100 levels instead of the 0–3 levels previously
  - A fan power supply gated through a regulator

This series adds support for this new variant by:

  1. Refactoring the khadas-mcu MFD driver to use per-variant data
     structures (regmap config, cells, fan platform data),
     and adding the khadas,vim4-mcu compatible string.

  2. Extending the fan thermal driver to retrieve the fan register
     and maximum level from platform_data,
     and to optionally manage a power regulator for the fan supply.

  3. Adding the corresponding DTS node for the VIM4, wiring the MCU to
     the I2C AO_A bus and exposing it as a thermal cooling device.

Signed-off-by: Ronald Claveau <[email protected]>
---
Changes in v9:
- Rebased on next-20260731 (patches 1/8, 2/8 and 6/8 already applied, dropped from this series).
- PATCH 1: Add levels table and nlevels in khadas_mcu_fan_pdata struct.
- PATCH 2: Use MFD_CELL_* macros instead of open-coding mfd_cell.
- PATCH 3: Provide levels table and nlevels to platform data.
           Check match_data before the switch.
- PATCH 4: Use levels[] and nlevels from platform data. VIM4 levels is (0, 30, 40, 55, 75, 100).
- Link to v8: https://lore.kernel.org/r/[email protected]

Changes in v8:
- PATCH 4: Define constant for fan max level, remove extra space for unnecessary alignment.
           Thanks to Lee's review.
- Link to v7: https://lore.kernel.org/r/[email protected]

Changes in v7:
- PATCH 3-4: Simplify the per-variant handling by using local variables in khadas_mcu_probe()
             instead of introducing a dedicated data structure. Thanks to Lee's review.
- Link to v6: https://lore.kernel.org/r/[email protected]

Changes in v6:
- PATCH 4: Address Lee's review comments:
  - Use an enum to discriminate between MCU types instead of passing
    MFD data through the DT match table
  - Fix error code from -EINVAL to -ENODEV when no MCU type is matched
  - Make khadas_mcu_fan_cells and khadas_mcu_cells const
  - Use dev_err_probe() for regmap initialization error
  - Document fan speed levels for max_level
- Link to v5: https://lore.kernel.org/r/[email protected]

Changes in v5:
- PATCH 5: Replace devm_regulator_get_optional() with devm_regulator_get()
           to simplify error handling and remove NULL checks, also
           ordering as reverse christmas according to Neil's feedback.
- Link to v4: https://lore.kernel.org/r/[email protected]

Changes in v4:
- PATCH 1: limit fan-supply property by compatible according to Conor's feedback.
- Link to v3: https://lore.kernel.org/r/[email protected]

Changes in v3:
- PATCH 1: adding comment on vim4 compatible saying it is not discoverable,
           thanks to Rob's and Neil's feedback.
- Link to v2: https://lore.kernel.org/r/[email protected]

Changes in v2:
- PATCH 5: Add regulator_disable on suspend thanks to Neil's feedback.
- Link to v1: https://lore.kernel.org/r/[email protected]

---
Ronald Claveau (6):
      mfd: khadas-mcu: Add per-variant configuration infrastructure and VIM4 support
      mfd: khadas-mcu: Use MFD_CELL_* macros for cell declarations
      mfd: khadas-mcu: Add support for VIM4 MCU variant
      thermal: khadas-mcu-fan: Add fan config from platform data Add regulator support
      arm64: dts: amlogic: t7: Add i2c controller node
      arm64: dts: amlogic: t7: khadas-vim4: Add i2c MCU fan node

 .../dts/amlogic/amlogic-t7-a311d2-khadas-vim4.dts  |  13 +++
 arch/arm64/boot/dts/amlogic/amlogic-t7.dtsi        |  10 ++
 drivers/mfd/khadas-mcu.c                           | 126 ++++++++++++++++++---
 drivers/thermal/khadas_mcu_fan.c                   |  58 +++++++---
 include/linux/mfd/khadas-mcu.h                     |  24 ++++
 5 files changed, 197 insertions(+), 34 deletions(-)
---
base-commit: 9dba66b6217aacb924d997de3866e7e4c0dcf952
change-id: 20260402-add-mcu-fan-khadas-vim4-ac1cbe553c9b

Best regards,
-- 
Ronald Claveau <[email protected]>