reboot-mode: Add NVMEM reboot mode

This adds an NVMEM reboot mode driver, similar to Linux's
implementation. This allows using the same device tree binding for Linux
and U-Boot in most cases.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

MAINTAINERS

@@ -1198,6 +1198,7 @@ M:	Sean Anderson <seanga2@gmail.com>
 S:	Maintained
 F:	doc/api/nvmem.rst
 F:	drivers/misc/nvmem.c
+F:	drivers/reboot-mode/reboot-mode-nvmem.c
 F:	include/nvmem.h
 
 NXP C45 TJA11XX PHY DRIVER

drivers/reboot-mode/Kconfig

@@ -30,4 +30,11 @@ config DM_REBOOT_MODE_RTC
 		a device in a specific mode by using a register(s) that can be controlled
 		outside U-Boot (e.g. Kernel).
 
+config REBOOT_MODE_NVMEM
+	bool "Use NVMEM reboot mode"
+	depends on DM_REBOOT_MODE && NVMEM
+	help
+	  Use any kind of non-volatile memory (EEPROM, RTC, etc) to control the
+	  reboot mode.
+
 endmenu

drivers/reboot-mode/Makefile

@@ -7,3 +7,4 @@
 obj-$(CONFIG_DM_REBOOT_MODE) += reboot-mode-uclass.o
 obj-$(CONFIG_DM_REBOOT_MODE_GPIO) += reboot-mode-gpio.o
 obj-$(CONFIG_DM_REBOOT_MODE_RTC) += reboot-mode-rtc.o
+obj-$(CONFIG_REBOOT_MODE_NVMEM) += reboot-mode-nvmem.o

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

+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2022 Sean Anderson <sean.anderson@seco.com>
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <nvmem.h>
+#include <reboot-mode/reboot-mode.h>
+
+/**
+ * struct nvmem_reboot_mode_priv - Private data for the nvmem reboot mode device
+ * @cell: The nvmem cell to store the mode in
+ */
+struct nvmem_reboot_mode_priv {
+	struct nvmem_cell cell;
+};
+
+static int reboot_mode_get(struct udevice *dev, u32 *mode)
+{
+	struct nvmem_reboot_mode_priv *priv = dev_get_priv(dev);
+
+	return nvmem_cell_read(&priv->cell, mode, sizeof(*mode));
+}
+
+static int reboot_mode_set(struct udevice *dev, u32 mode)
+{
+	struct nvmem_reboot_mode_priv *priv = dev_get_priv(dev);
+
+	return nvmem_cell_write(&priv->cell, &mode, sizeof(mode));
+}
+
+static const struct reboot_mode_ops nvmem_reboot_mode_ops = {
+	.get = reboot_mode_get,
+	.set = reboot_mode_set,
+};
+
+static int reboot_mode_probe(struct udevice *dev)
+{
+	struct nvmem_reboot_mode_priv *priv = dev_get_priv(dev);
+
+	return nvmem_cell_get_by_name(dev, "reboot-mode", &priv->cell);
+}
+
+static const struct udevice_id nvmem_reboot_mode_ids[] = {
+	{ .compatible = "nvmem-reboot-mode" },
+	{ }
+};
+
+U_BOOT_DRIVER(nvmem_reboot_mode) = {
+	.name = "nvmem-reboot-mode",
+	.id = UCLASS_REBOOT_MODE,
+	.of_match = nvmem_reboot_mode_ids,
+	.probe = reboot_mode_probe,
+	.priv_auto = sizeof(struct nvmem_reboot_mode_priv),
+	.ops = &nvmem_reboot_mode_ops,
+};