nvmem: max77759: Add Maxim MAX77759 NVMEM driver

The Maxim MAX77759 is a companion PMIC for USB Type-C applications and
includes Battery Charger, Fuel Gauge, temperature sensors, USB Type-C
Port Controller (TCPC), NVMEM, and a GPIO expander.

This driver exposes the non volatile memory using the platform device
registered by the core MFD driver.

Signed-off-by: André Draszik <andre.draszik@linaro.org>
Acked-by: Srinivas Kandagatla <srini@kernel.org>
Acked-by: Peter Griffin <peter.griffin@linaro.org>
Link: https://lore.kernel.org/r/20250509-max77759-mfd-v10-3-962ac15ee3ef@linaro.org
Signed-off-by: Lee Jones <lee@kernel.org>

MAINTAINERS

@@ -14582,6 +14582,7 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/*/maxim,max77759*.yaml
 F:	drivers/gpio/gpio-max77759.c
 F:	drivers/mfd/max77759.c
+F:	drivers/nvmem/max77759-nvmem.c
 F:	include/linux/mfd/max77759.h
 
 MAXIM MAX77802 PMIC REGULATOR DEVICE DRIVER

drivers/nvmem/Kconfig

@@ -154,6 +154,18 @@ config NVMEM_LPC18XX_OTP
 	  To compile this driver as a module, choose M here: the module
 	  will be called nvmem_lpc18xx_otp.
 
+config NVMEM_MAX77759
+	tristate "Maxim Integrated MAX77759 NVMEM Support"
+	depends on MFD_MAX77759
+	default MFD_MAX77759
+	help
+	  Say Y here to include support for the user-accessible storage found
+	  in Maxim Integrated MAX77759 PMICs. This IC provides space for 30
+	  bytes of storage.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called nvmem-max77759.
+
 config NVMEM_MESON_EFUSE
 	tristate "Amlogic Meson GX eFuse Support"
 	depends on (ARCH_MESON || COMPILE_TEST) && MESON_SM

drivers/nvmem/Makefile

@@ -34,6 +34,8 @@ obj-$(CONFIG_NVMEM_LPC18XX_EEPROM)	+= nvmem_lpc18xx_eeprom.o
 nvmem_lpc18xx_eeprom-y			:= lpc18xx_eeprom.o
 obj-$(CONFIG_NVMEM_LPC18XX_OTP)		+= nvmem_lpc18xx_otp.o
 nvmem_lpc18xx_otp-y			:= lpc18xx_otp.o
+obj-$(CONFIG_NVMEM_MAX77759)		+= nvmem-max77759.o
+nvmem-max77759-y			:= max77759-nvmem.o
 obj-$(CONFIG_NVMEM_MESON_EFUSE)		+= nvmem_meson_efuse.o
 nvmem_meson_efuse-y			:= meson-efuse.o
 obj-$(CONFIG_NVMEM_MESON_MX_EFUSE)	+= nvmem_meson_mx_efuse.o

drivers/nvmem/max77759-nvmem.c

@@ -0,0 +1,145 @@
+// SPDX-License-Identifier: GPL-2.0-only
+//
+// Copyright 2020 Google Inc
+// Copyright 2025 Linaro Ltd.
+//
+// NVMEM driver for Maxim MAX77759
+
+#include <linux/dev_printk.h>
+#include <linux/device.h>
+#include <linux/device/driver.h>
+#include <linux/err.h>
+#include <linux/mfd/max77759.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/overflow.h>
+#include <linux/platform_device.h>
+#include <linux/string.h>
+
+#define MAX77759_NVMEM_OPCODE_HEADER_LEN 3
+/*
+ * NVMEM commands have a three byte header (which becomes part of the command),
+ * so we need to subtract that.
+ */
+#define MAX77759_NVMEM_SIZE (MAX77759_MAXQ_OPCODE_MAXLENGTH \
+			     - MAX77759_NVMEM_OPCODE_HEADER_LEN)
+
+struct max77759_nvmem {
+	struct device *dev;
+	struct max77759 *max77759;
+};
+
+static int max77759_nvmem_reg_read(void *priv, unsigned int offset,
+				   void *val, size_t bytes)
+{
+	struct max77759_nvmem *nvmem = priv;
+	DEFINE_FLEX(struct max77759_maxq_command, cmd, cmd, length,
+		    MAX77759_NVMEM_OPCODE_HEADER_LEN);
+	DEFINE_FLEX(struct max77759_maxq_response, rsp, rsp, length,
+		    MAX77759_MAXQ_OPCODE_MAXLENGTH);
+	int ret;
+
+	cmd->cmd[0] = MAX77759_MAXQ_OPCODE_USER_SPACE_READ;
+	cmd->cmd[1] = offset;
+	cmd->cmd[2] = bytes;
+	rsp->length = bytes + MAX77759_NVMEM_OPCODE_HEADER_LEN;
+
+	ret = max77759_maxq_command(nvmem->max77759, cmd, rsp);
+	if (ret < 0)
+		return ret;
+
+	if (memcmp(cmd->cmd, rsp->rsp, MAX77759_NVMEM_OPCODE_HEADER_LEN)) {
+		dev_warn(nvmem->dev, "protocol error (read)\n");
+		return -EIO;
+	}
+
+	memcpy(val, &rsp->rsp[MAX77759_NVMEM_OPCODE_HEADER_LEN], bytes);
+
+	return 0;
+}
+
+static int max77759_nvmem_reg_write(void *priv, unsigned int offset,
+				    void *val, size_t bytes)
+{
+	struct max77759_nvmem *nvmem = priv;
+	DEFINE_FLEX(struct max77759_maxq_command, cmd, cmd, length,
+		    MAX77759_MAXQ_OPCODE_MAXLENGTH);
+	DEFINE_FLEX(struct max77759_maxq_response, rsp, rsp, length,
+		    MAX77759_MAXQ_OPCODE_MAXLENGTH);
+	int ret;
+
+	cmd->cmd[0] = MAX77759_MAXQ_OPCODE_USER_SPACE_WRITE;
+	cmd->cmd[1] = offset;
+	cmd->cmd[2] = bytes;
+	memcpy(&cmd->cmd[MAX77759_NVMEM_OPCODE_HEADER_LEN], val, bytes);
+	cmd->length = bytes + MAX77759_NVMEM_OPCODE_HEADER_LEN;
+	rsp->length = cmd->length;
+
+	ret = max77759_maxq_command(nvmem->max77759, cmd, rsp);
+	if (ret < 0)
+		return ret;
+
+	if (memcmp(cmd->cmd, rsp->rsp, cmd->length)) {
+		dev_warn(nvmem->dev, "protocol error (write)\n");
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int max77759_nvmem_probe(struct platform_device *pdev)
+{
+	struct nvmem_config config = {
+		.dev = &pdev->dev,
+		.name = dev_name(&pdev->dev),
+		.id = NVMEM_DEVID_NONE,
+		.type = NVMEM_TYPE_EEPROM,
+		.ignore_wp = true,
+		.size = MAX77759_NVMEM_SIZE,
+		.word_size = sizeof(u8),
+		.stride = sizeof(u8),
+		.reg_read = max77759_nvmem_reg_read,
+		.reg_write = max77759_nvmem_reg_write,
+	};
+	struct max77759_nvmem *nvmem;
+
+	nvmem = devm_kzalloc(&pdev->dev, sizeof(*nvmem), GFP_KERNEL);
+	if (!nvmem)
+		return -ENOMEM;
+
+	nvmem->dev = &pdev->dev;
+	nvmem->max77759 = dev_get_drvdata(pdev->dev.parent);
+
+	config.priv = nvmem;
+
+	return PTR_ERR_OR_ZERO(devm_nvmem_register(config.dev, &config));
+}
+
+static const struct of_device_id max77759_nvmem_of_id[] = {
+	{ .compatible = "maxim,max77759-nvmem", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, max77759_nvmem_of_id);
+
+static const struct platform_device_id max77759_nvmem_platform_id[] = {
+	{ "max77759-nvmem", },
+	{ }
+};
+MODULE_DEVICE_TABLE(platform, max77759_nvmem_platform_id);
+
+static struct platform_driver max77759_nvmem_driver = {
+	.driver = {
+		.name = "max77759-nvmem",
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+		.of_match_table = max77759_nvmem_of_id,
+	},
+	.probe = max77759_nvmem_probe,
+	.id_table = max77759_nvmem_platform_id,
+};
+
+module_platform_driver(max77759_nvmem_driver);
+
+MODULE_AUTHOR("André Draszik <andre.draszik@linaro.org>");
+MODULE_DESCRIPTION("NVMEM driver for Maxim MAX77759");
+MODULE_LICENSE("GPL");