[PATCH v4 0/2] Use NVMEM as reboot-mode write interface

[Han Nandor]

Description
-----------
Extend the reboot mode driver to use a NVMEM cell as writing interface.

Testing
-------
The testing is done by configuring DT from a custom board.
The NVMEM cell is configured in an RTC non-volatile memory.
Kernel: 4.14.60 (the patchset was rebased on kernel master)

DT configurations:
`
...
reboot-mode-nvmem@0 {
    compatible = "simple-mfd";
    reboot-mode {
        compatible = "nvmem-reboot-mode";
        nvmem-cells = <&reboot_mode>;
        nvmem-cell-names = "reboot-mode";

        mode-test       = <0x21969147>;
    };
};
...
reboot_mode: nvmem_reboot_mode@0 {
        reg = <0x00 0x4>;
};
...
`

1. Reboot the system using the command `reboot test`

2. Verify that kernel logs show that reboot was done in mode `test`:
PASS
`[  413.957172] reboot: Restarting system with command 'test' `

3. Stop in U-Boot and verify that mode `test` magic value is present
in RTCs non-volatile memory: PASS

Kernel: 5.1.0-rc3

1. Configure `arch/arm/configs/imx_v6_v7_defconfig` to contain 
`CONFIG_NVMEM_REBOOT_MODE=y`
2. Verify that Kernel compiles successful: PASS
`
make ARCH=arm CROSS_COMPILE=arm-linux-gnu- imx_v6_v7_defconfig zImage
...
CC      drivers/power/reset/nvmem-reboot-mode.o
...
Kernel: arch/arm/boot/zImage is ready
`
Changes since v1:
-----------------
 - split the documentation on a separate patch
 - add a missing header

Changes since v2:
----------------
 - change the module license to GPL since GPL v2 is deprecated

Changes since v3:
----------------
 - documentation updated according to the comments

Nandor Han (2):
  power: reset: nvmem-reboot-mode: use NVMEM as reboot mode write
    interface
  dt-bindings: power: reset: add document for NVMEM based reboot-mode

 .../power/reset/nvmem-reboot-mode.txt         | 26 +++++++
 drivers/power/reset/Kconfig                   |  9 +++
 drivers/power/reset/Makefile                  |  1 +
 drivers/power/reset/nvmem-reboot-mode.c       | 76 +++++++++++++++++++
 4 files changed, 112 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/power/reset/nvmem-reboot-mode.txt
 create mode 100644 drivers/power/reset/nvmem-reboot-mode.c

-- 
2.17.2