power: reset: nvmem-reboot-mode: use NVMEM as reboot mode write interface

Add a new reboot mode write interface that is using an NVMEM cell
to store the reboot mode magic.

Signed-off-by: Nandor Han <[e-mail]>
Signed-off-by: Sebastian Reichel <[e-mail]>

drivers/power/reset/Kconfig

···
 	  PMICs includes the SC2720, SC2721, SC2723, SC2730
 	  and SC2731 chips.
 
+config NVMEM_REBOOT_MODE
+	tristate "Generic NVMEM reboot mode driver"
+	select REBOOT_MODE
+	help
+	  Say y here will enable reboot mode driver. This will
+	  get reboot mode arguments and store it in a NVMEM cell,
+	  then the bootloader can read it and take different
+	  action according to the mode.
+
 endif
 

drivers/power/reset/Makefile

···
 obj-$(CONFIG_REBOOT_MODE) += reboot-mode.o
 obj-$(CONFIG_SYSCON_REBOOT_MODE) += syscon-reboot-mode.o
 obj-$(CONFIG_POWER_RESET_SC27XX) += sc27xx-poweroff.o
+obj-$(CONFIG_NVMEM_REBOOT_MODE) += nvmem-reboot-mode.o

drivers/power/reset/nvmem-reboot-mode.c

···
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) Vaisala Oyj. All rights reserved.
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/of.h>
+#include <linux/nvmem-consumer.h>
+#include <linux/platform_device.h>
+#include <linux/reboot-mode.h>
+
+struct nvmem_reboot_mode {
+	struct reboot_mode_driver reboot;
+	struct nvmem_cell *cell;
+};
+
+static int nvmem_reboot_mode_write(struct reboot_mode_driver *reboot,
+				    unsigned int magic)
+{
+	int ret;
+	struct nvmem_reboot_mode *nvmem_rbm;
+
+	nvmem_rbm = container_of(reboot, struct nvmem_reboot_mode, reboot);
+
+	ret = nvmem_cell_write(nvmem_rbm->cell, &magic, sizeof(magic));
+	if (ret < 0)
+		dev_err(reboot->dev, "update reboot mode bits failed\n");
+
+	return ret;
+}
+
+static int nvmem_reboot_mode_probe(struct platform_device *pdev)
+{
+	int ret;
+	struct nvmem_reboot_mode *nvmem_rbm;
+
+	nvmem_rbm = devm_kzalloc(&pdev->dev, sizeof(*nvmem_rbm), GFP_KERNEL);
+	if (!nvmem_rbm)
+		return -ENOMEM;
+
+	nvmem_rbm->reboot.dev = &pdev->dev;
+	nvmem_rbm->reboot.write = nvmem_reboot_mode_write;
+
+	nvmem_rbm->cell = devm_nvmem_cell_get(&pdev->dev, "reboot-mode");
+	if (IS_ERR(nvmem_rbm->cell)) {
+		dev_err(&pdev->dev, "failed to get the nvmem cell reboot-mode\n");
+		return PTR_ERR(nvmem_rbm->cell);
+	}
+
+	ret = devm_reboot_mode_register(&pdev->dev, &nvmem_rbm->reboot);
+	if (ret)
+		dev_err(&pdev->dev, "can't register reboot mode\n");
+
+	return ret;
+}
+
+static const struct of_device_id nvmem_reboot_mode_of_match[] = {
+	{ .compatible = "nvmem-reboot-mode" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, nvmem_reboot_mode_of_match);
+
+static struct platform_driver nvmem_reboot_mode_driver = {
+	.probe = nvmem_reboot_mode_probe,
+	.driver = {
+		.name = "nvmem-reboot-mode",
+		.of_match_table = nvmem_reboot_mode_of_match,
+	},
+};
+module_platform_driver(nvmem_reboot_mode_driver);
+
+MODULE_AUTHOR("Nandor Han <[e-mail]>");
+MODULE_DESCRIPTION("NVMEM reboot mode driver");
+MODULE_LICENSE("GPL");