doc: services: Add NVMEM subsystem

Introduce a page for the Non-Volatile Memory subsystem with a reference to
the doxygen API.

Signed-off-by: Pieter De Gendt <[email protected]>

Author: pdgendt

doc/services/index.rst

@@ -24,6 +24,7 @@ OS Services
    resource_management/index.rst
    mem_mgmt/index.rst
    net_buf/index.rst
+   nvmem/index.rst
    modem/index.rst
    notify.rst
    pm/index.rst

doc/services/nvmem/devicetree_bindings.txt

@@ -0,0 +1,18 @@
+&eeprom0 {
+	nvmem-layout {
+		compatible = "fixed-layout";
+		#address-cells = <1>;
+		#size-cells = <1>;
+
+		mac_address: mac_address@0 {
+			reg = <0x0 6>;
+			#nvmem-cell-cells = <0>;
+			read-only;
+		};
+
+		calibration_data: calibration_data@6 {
+			reg = <0x6 100>;
+			#nvmem-cell-cells = <0>;
+		};
+	};
+};

doc/services/nvmem/index.rst

@@ -0,0 +1,68 @@
+.. _nvmem:
+
+Non-Volatile Memory (NVMEM)
+###########################
+
+The NVMEM subsystem provides a generic interface for accessing non-volatile
+memory devices. It abstracts the underlying hardware and provides a unified API
+for reading and writing data.
+
+Key Concepts
+************
+
+NVMEM Provider
+==============
+
+An NVMEM provider is a driver that exposes NVMEM cells. For example, an EEPROM
+driver can be an NVMEM provider. The NVMEM provider is responsible for reading
+and writing data to the underlying hardware.
+
+NVMEM Cell
+==========
+
+An NVMEM cell is a region of non-volatile memory. It is defined in the
+devicetree and has properties like offset, size, and read-only status.
+
+NVMEM Consumer
+==============
+
+An NVMEM consumer is a driver or application that uses NVMEM cells to store or
+retrieve data.
+
+Configuration
+*************
+
+* :kconfig:option:`CONFIG_NVMEM`: Enables the NVMEM subsystem.
+* :kconfig:option:`CONFIG_NVMEM_EEPROM`: Enables NVMEM support for EEPROM devices.
+
+Devicetree Bindings
+*******************
+
+The NVMEM subsystem relies on devicetree bindings to define NVMEM cells.
+The following is an example of how to define an NVMEM provider and cells in the
+devicetree:
+
+.. literalinclude:: devicetree_bindings.txt
+   :language: dts
+
+
+A consumer can then reference the NVMEM cells like this:
+
+.. literalinclude:: my_consumer.txt
+   :language: dts
+
+
+Usage Example
+*************
+
+The following is an example of how to use the NVMEM API to read data from an
+NVMEM cell:
+
+.. literalinclude:: usage_example.txt
+   :language: c
+
+
+API Reference
+*************
+
+.. doxygengroup:: nvmem_interface

doc/services/nvmem/my_consumer.txt

@@ -0,0 +1,5 @@
+my_consumer: my-consumer {
+	compatible = "my,consumer";
+	nvmem-cells = <&mac_address>, <&calibration_data>;
+	nvmem-cell-names = "mac-address", "calibration-data";
+};

doc/services/nvmem/usage_example.txt

@@ -0,0 +1,23 @@
+#include <zephyr/nvmem.h>
+
+static const struct nvmem_cell mac_address =
+	NVMEM_CELL_GET_BY_NAME(DT_NODELABEL(my_consumer), mac_address);
+
+int main(void)
+{
+	uint8_t mac[6];
+	int ret;
+
+	if (!nvmem_cell_is_ready(&mac_address)) {
+		printk("NVMEM cell is not ready\n");
+		return -ENODEV;
+	}
+
+	ret = nvmem_cell_read(&mac_address, mac, 0, sizeof(mac));
+	if (ret < 0) {
+		printk("Failed to read MAC address: %d\n", ret);
+		return ret;
+	}
+
+	/* ... */
+}