2015-07-27 19:14:14 +08:00
|
|
|
NVMEM SUBSYSTEM
|
|
|
|
Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
|
|
|
|
|
|
|
|
This document explains the NVMEM Framework along with the APIs provided,
|
|
|
|
and how to use it.
|
|
|
|
|
|
|
|
1. Introduction
|
|
|
|
===============
|
|
|
|
*NVMEM* is the abbreviation for Non Volatile Memory layer. It is used to
|
|
|
|
retrieve configuration of SOC or Device specific data from non volatile
|
|
|
|
memories like eeprom, efuses and so on.
|
|
|
|
|
|
|
|
Before this framework existed, NVMEM drivers like eeprom were stored in
|
|
|
|
drivers/misc, where they all had to duplicate pretty much the same code to
|
|
|
|
register a sysfs file, allow in-kernel users to access the content of the
|
|
|
|
devices they were driving, etc.
|
|
|
|
|
|
|
|
This was also a problem as far as other in-kernel users were involved, since
|
|
|
|
the solutions used were pretty much different from one driver to another, there
|
|
|
|
was a rather big abstraction leak.
|
|
|
|
|
|
|
|
This framework aims at solve these problems. It also introduces DT
|
|
|
|
representation for consumer devices to go get the data they require (MAC
|
|
|
|
Addresses, SoC/Revision ID, part numbers, and so on) from the NVMEMs. This
|
|
|
|
framework is based on regmap, so that most of the abstraction available in
|
|
|
|
regmap can be reused, across multiple types of buses.
|
|
|
|
|
|
|
|
NVMEM Providers
|
|
|
|
+++++++++++++++
|
|
|
|
|
|
|
|
NVMEM provider refers to an entity that implements methods to initialize, read
|
|
|
|
and write the non-volatile memory.
|
|
|
|
|
|
|
|
2. Registering/Unregistering the NVMEM provider
|
|
|
|
===============================================
|
|
|
|
|
|
|
|
A NVMEM provider can register with NVMEM core by supplying relevant
|
|
|
|
nvmem configuration to nvmem_register(), on success core would return a valid
|
|
|
|
nvmem_device pointer.
|
|
|
|
|
|
|
|
nvmem_unregister(nvmem) is used to unregister a previously registered provider.
|
|
|
|
|
|
|
|
For example, a simple qfprom case:
|
|
|
|
|
|
|
|
static struct nvmem_config econfig = {
|
|
|
|
.name = "qfprom",
|
|
|
|
.owner = THIS_MODULE,
|
|
|
|
};
|
|
|
|
|
|
|
|
static int qfprom_probe(struct platform_device *pdev)
|
|
|
|
{
|
|
|
|
...
|
|
|
|
econfig.dev = &pdev->dev;
|
|
|
|
nvmem = nvmem_register(&econfig);
|
|
|
|
...
|
|
|
|
}
|
|
|
|
|
|
|
|
It is mandatory that the NVMEM provider has a regmap associated with its
|
|
|
|
struct device. Failure to do would return error code from nvmem_register().
|
|
|
|
|
2018-09-21 21:40:18 +08:00
|
|
|
Users of board files can define and register nvmem cells using the
|
|
|
|
nvmem_cell_table struct:
|
|
|
|
|
|
|
|
static struct nvmem_cell_info foo_nvmem_cells[] = {
|
|
|
|
{
|
|
|
|
.name = "macaddr",
|
|
|
|
.offset = 0x7f00,
|
|
|
|
.bytes = ETH_ALEN,
|
|
|
|
}
|
|
|
|
};
|
|
|
|
|
|
|
|
static struct nvmem_cell_table foo_nvmem_cell_table = {
|
|
|
|
.nvmem_name = "i2c-eeprom",
|
|
|
|
.cells = foo_nvmem_cells,
|
|
|
|
.ncells = ARRAY_SIZE(foo_nvmem_cells),
|
|
|
|
};
|
|
|
|
|
|
|
|
nvmem_add_cell_table(&foo_nvmem_cell_table);
|
|
|
|
|
|
|
|
Additionally it is possible to create nvmem cell lookup entries and register
|
|
|
|
them with the nvmem framework from machine code as shown in the example below:
|
|
|
|
|
|
|
|
static struct nvmem_cell_lookup foo_nvmem_lookup = {
|
|
|
|
.nvmem_name = "i2c-eeprom",
|
|
|
|
.cell_name = "macaddr",
|
|
|
|
.dev_id = "foo_mac.0",
|
|
|
|
.con_id = "mac-address",
|
|
|
|
};
|
|
|
|
|
|
|
|
nvmem_add_cell_lookups(&foo_nvmem_lookup, 1);
|
|
|
|
|
2015-07-27 19:14:14 +08:00
|
|
|
NVMEM Consumers
|
|
|
|
+++++++++++++++
|
|
|
|
|
|
|
|
NVMEM consumers are the entities which make use of the NVMEM provider to
|
|
|
|
read from and to NVMEM.
|
|
|
|
|
|
|
|
3. NVMEM cell based consumer APIs
|
|
|
|
=================================
|
|
|
|
|
|
|
|
NVMEM cells are the data entries/fields in the NVMEM.
|
|
|
|
The NVMEM framework provides 3 APIs to read/write NVMEM cells.
|
|
|
|
|
|
|
|
struct nvmem_cell *nvmem_cell_get(struct device *dev, const char *name);
|
|
|
|
struct nvmem_cell *devm_nvmem_cell_get(struct device *dev, const char *name);
|
|
|
|
|
|
|
|
void nvmem_cell_put(struct nvmem_cell *cell);
|
|
|
|
void devm_nvmem_cell_put(struct device *dev, struct nvmem_cell *cell);
|
|
|
|
|
|
|
|
void *nvmem_cell_read(struct nvmem_cell *cell, ssize_t *len);
|
|
|
|
int nvmem_cell_write(struct nvmem_cell *cell, void *buf, ssize_t len);
|
|
|
|
|
|
|
|
*nvmem_cell_get() apis will get a reference to nvmem cell for a given id,
|
|
|
|
and nvmem_cell_read/write() can then read or write to the cell.
|
|
|
|
Once the usage of the cell is finished the consumer should call *nvmem_cell_put()
|
|
|
|
to free all the allocation memory for the cell.
|
|
|
|
|
|
|
|
4. Direct NVMEM device based consumer APIs
|
|
|
|
==========================================
|
|
|
|
|
|
|
|
In some instances it is necessary to directly read/write the NVMEM.
|
|
|
|
To facilitate such consumers NVMEM framework provides below apis.
|
|
|
|
|
|
|
|
struct nvmem_device *nvmem_device_get(struct device *dev, const char *name);
|
|
|
|
struct nvmem_device *devm_nvmem_device_get(struct device *dev,
|
|
|
|
const char *name);
|
|
|
|
void nvmem_device_put(struct nvmem_device *nvmem);
|
|
|
|
int nvmem_device_read(struct nvmem_device *nvmem, unsigned int offset,
|
|
|
|
size_t bytes, void *buf);
|
|
|
|
int nvmem_device_write(struct nvmem_device *nvmem, unsigned int offset,
|
|
|
|
size_t bytes, void *buf);
|
|
|
|
int nvmem_device_cell_read(struct nvmem_device *nvmem,
|
|
|
|
struct nvmem_cell_info *info, void *buf);
|
|
|
|
int nvmem_device_cell_write(struct nvmem_device *nvmem,
|
|
|
|
struct nvmem_cell_info *info, void *buf);
|
|
|
|
|
|
|
|
Before the consumers can read/write NVMEM directly, it should get hold
|
|
|
|
of nvmem_controller from one of the *nvmem_device_get() api.
|
|
|
|
|
|
|
|
The difference between these apis and cell based apis is that these apis always
|
|
|
|
take nvmem_device as parameter.
|
|
|
|
|
|
|
|
5. Releasing a reference to the NVMEM
|
|
|
|
=====================================
|
|
|
|
|
2017-08-17 06:45:57 +08:00
|
|
|
When a consumer no longer needs the NVMEM, it has to release the reference
|
2015-07-27 19:14:14 +08:00
|
|
|
to the NVMEM it has obtained using the APIs mentioned in the above section.
|
|
|
|
The NVMEM framework provides 2 APIs to release a reference to the NVMEM.
|
|
|
|
|
|
|
|
void nvmem_cell_put(struct nvmem_cell *cell);
|
|
|
|
void devm_nvmem_cell_put(struct device *dev, struct nvmem_cell *cell);
|
|
|
|
void nvmem_device_put(struct nvmem_device *nvmem);
|
|
|
|
void devm_nvmem_device_put(struct device *dev, struct nvmem_device *nvmem);
|
|
|
|
|
|
|
|
Both these APIs are used to release a reference to the NVMEM and
|
|
|
|
devm_nvmem_cell_put and devm_nvmem_device_put destroys the devres associated
|
|
|
|
with this NVMEM.
|
|
|
|
|
|
|
|
Userspace
|
|
|
|
+++++++++
|
|
|
|
|
|
|
|
6. Userspace binary interface
|
|
|
|
==============================
|
|
|
|
|
|
|
|
Userspace can read/write the raw NVMEM file located at
|
|
|
|
/sys/bus/nvmem/devices/*/nvmem
|
|
|
|
|
|
|
|
ex:
|
|
|
|
|
|
|
|
hexdump /sys/bus/nvmem/devices/qfprom0/nvmem
|
|
|
|
|
|
|
|
0000000 0000 0000 0000 0000 0000 0000 0000 0000
|
|
|
|
*
|
|
|
|
00000a0 db10 2240 0000 e000 0c00 0c00 0000 0c00
|
|
|
|
0000000 0000 0000 0000 0000 0000 0000 0000 0000
|
|
|
|
...
|
|
|
|
*
|
|
|
|
0001000
|
|
|
|
|
|
|
|
7. DeviceTree Binding
|
|
|
|
=====================
|
|
|
|
|
|
|
|
See Documentation/devicetree/bindings/nvmem/nvmem.txt
|