---
name: "nvmem"
section: "9"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd"]
url: "https://new.carta.tech/nvmem"
---

# nvmem(9)

## NAME

**nvmem**, **nvmem\_get\_cell\_len**, **nvmem\_read\_cell\_by\_name**, **nvmem\_read\_cell\_by\_idx**, **nvmem\_write\_cell\_by\_name**, **nvmem\_write\_cell\_by\_idx**

## SYNOPSIS

**options FDT** **device nvmem**

**#include \<sys/extres/nvmem/nvmem.h\>**

*int*\

**nvmem\_get\_cell\_len**(*phandle\_t node*, *const char \*name*);

*int*\

**nvmem\_read\_cell\_by\_name**(*phandle\_t node*, *const char \*name*, *void \*cell*, *size\_t buflen*);

*int*\

**nvmem\_read\_cell\_by\_idx**(*phandle\_t node*, *int idx*, *void \*cell*, *size\_t buflen*);

*int*\

**nvmem\_write\_cell\_by\_name**(*phandle\_t node*, *const char \*name*, *void \*cell*, *size\_t buflen*);

*int*\

**nvmem\_write\_cell\_by\_idx**(*phandle\_t node*, *int idx*, *void \*cell*, *size\_t buflen*);

## DESCRIPTION

On some embedded boards, the manufacturer stored some data on a NVMEM (Non-Volatile Memory), this is generally stored in some eeprom or fuses.

The **nvmem** API consist of helpers functions for consumer and device methods for providers.

## FUNCTIONS

- **nvmem\_get\_cell\_len**(*phandle\_t node*, *const char \*name*)

  Get the size of the cell base on the reg property on the node. Return the size or ENOENT if the cell name wasn't found

- **nvmem\_read\_cell\_by\_name**(*phandle\_t node*, *const char \*name*, *void \*cell*, *size\_t buflen*)

  Get the cell content based on the name. Return 0 on success or ENOENT if the cell doesn't exists, ENXIO if no provider device was found, EINVAL if the size isn't correct.

- **nvmem\_read\_cell\_by\_idx**(*phandle\_t node*, *int idx*, *void \*cell*, *size\_t buflen*)

  Get the cell content based on the id. Return 0 on success or ENOENT if the cell doesn't exists, ENXIO if no provider device was found, EINVAL if the size isn't correct.

- **nvmem\_write\_cell\_by\_name**(*phandle\_t node*, *const char \*name*, *void \*cell*, *size\_t buflen*)

  Write the cell content based on the name. Return 0 on success or ENOENT if the cell doesn't exists, ENXIO if no provider device was found, EINVAL if the size isn't correct.

- **nvmem\_write\_cell\_by\_idx**(*phandle\_t node*, *int idx*, *void \*cell*, *size\_t buflen*)

  Write the cell content based on the id. Return 0 on success or ENOENT if the cell doesn't exists, ENXIO if no provider device was found, EINVAL if the size isn't correct.

## DEVICE METHODS

- **nvmem\_read**(*device\_t dev*, *uint32\_t offset*, *uint32\_t size*, *uint8\_t \*buffer*)

  Provider device method to read a cell content.

- **nvmem\_write**(*device\_t dev*, *uint32\_t offset*, *uint32\_t size*, *uint8\_t \*buffer*)

  Provider device method to write a cell content.

## EXAMPLES

Consider this DTS

```
/* Provider */
eeprom: eeprom@20000 {
	board_id: id@0 {
		reg = <0x0 0x4>;
	};
};
/* Consumer */
device@30000 {
	...
	nvmem-cells = <&board_id>
	nvmem-cell-names = "boardid";
};
```

The device driver for eeprom@20000 needs to expose itself as a provider

```
#include "nvmem_if.h"
int
foo_nvmem_read(device_t dev, uint32_t offset, uint32_t size, uint8_t *buffer)
{
	/* Read the data */
}
int
foo_attach(device_t dev)
{
	phandle_t node;
	node = ofw_bus_get_node(dev);
	...
	/* Registering the device so the consumers can find us */
	OF_device_register_xref(OF_xref_from_node(node), dev);
	...
}
static device_method_t foo_methods[] = {
	...
	/* nvmem interface */
	DEVMETHOD(nvmem_read, foo_nvmem_read),
	/* Terminate method list */
	DEVMETHOD_END
};
```

The consumer device driver for device@30000 can now read the nvmem data

```
int
bar_attach(device_t dev)
{
	phandle_t node;
	uint32_t boardid;
	...
	node = ofw_bus_get_node(dev);
	nvmem_read_cell_by_name(node, "boardid", (void *)&boardid, sizeof(boardid));
	...
}
```

## HISTORY

The nvmem related function first appear in FreeBSD 12.0. The nvmem interface and manual page was written by Emmanuel Vadot ⟨*manu@FreeBSD.org*⟩.