NVMEM API

The NVMEM subsystem is a “meta-uclass” in that it abstracts over several different uclasses all with read/write APIs. One approach to implementing this could be to add a new sub-device for each nvmem-style device of UCLASS_NVMEM. This subsystem has taken the approach of using the existing access methods (i2c_eeprom_write, misc_write, etc.) directly. This has the advantage of not requiring an extra device/driver, saving on binary size and runtime memory usage. On the other hand, it is not idiomatic. Similar efforts should generally use a new uclass.

struct nvmem_cell: One datum within non-volatile memory

Definition

struct nvmem_cell {
  struct udevice *nvmem;
  unsigned int offset;
  size_t size;
};

Members

nvmem: The backing storage device
offset: The offset of the cell from the start of nvmem
size: The size of the cell, in bytes

int nvmem_cell_read(struct nvmem_cell *cell, void *buf, size_t size): Read the value of an nvmem cell

Parameters

struct nvmem_cell *cell: The nvmem cell to read
void *buf: The buffer to read into
size_t size: The size of buf

Return

0 on success
-EINVAL if buf is not the same size as cell.
-ENOSYS if CONFIG_NVMEM is disabled
A negative error if there was a problem reading the underlying storage

int nvmem_cell_write(struct nvmem_cell *cell, const void *buf, size_t size): Write a value to an nvmem cell

Parameters

struct nvmem_cell *cell: The nvmem cell to write
const void *buf: The buffer to write from
size_t size: The size of buf

Return

0 on success
-EINVAL if buf is not the same size as cell
-ENOSYS if cell is read-only, or if CONFIG_NVMEM is disabled
A negative error if there was a problem writing the underlying storage

int nvmem_cell_get_by_index(struct udevice *dev, int index, struct nvmem_cell *cell): Get an nvmem cell from a given device and index

Parameters

struct udevice *dev: The device that uses the nvmem cell
int index: The index of the cell in nvmem-cells
struct nvmem_cell *cell: The cell to initialize

Description

Look up the nvmem cell referenced by the phandle at index in nvmem-cells in dev.

Return

0 on success
-EINVAL if the regs property is missing, empty, or undersized
-ENODEV if the nvmem device is missing or unimplemented
-ENOSYS if CONFIG_NVMEM is disabled
A negative error if there was a problem reading nvmem-cells or getting the device

int nvmem_cell_get_by_name(struct udevice *dev, const char *name, struct nvmem_cell *cell): Get an nvmem cell from a given device and name

Parameters

struct udevice *dev: The device that uses the nvmem cell
const char *name: The name of the nvmem cell
struct nvmem_cell *cell: The cell to initialize

Description

Look up the nvmem cell referenced by name in the nvmem-cell-names property of dev.

Return

0 on success
-EINVAL if the regs property is missing, empty, or undersized
-ENODEV if the nvmem device is missing or unimplemented
-ENODATA if name is not in nvmem-cell-names
-ENOSYS if CONFIG_NVMEM is disabled
A negative error if there was a problem reading nvmem-cell-names, nvmem-cells, or getting the device