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author | Mauro Carvalho Chehab <mchehab+samsung@kernel.org> | 2019-06-27 21:39:22 +0300 |
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committer | Mauro Carvalho Chehab <mchehab+samsung@kernel.org> | 2019-07-15 17:03:02 +0300 |
commit | baa293e9544bea71361950d071579f0e4d5713ed (patch) | |
tree | 29e0400c806016783a3fd7a380be40a201956653 /Documentation/nvmem | |
parent | 4f4cfa6c560c93ba180c30675cf845e1597de44c (diff) | |
download | linux-baa293e9544bea71361950d071579f0e4d5713ed.tar.xz |
docs: driver-api: add a series of orphaned documents
There are lots of documents under Documentation/*.txt and a few other
orphan documents elsehwere that belong to the driver-API book.
Move them to their right place.
Reviewed-by: Cornelia Huck <cohuck@redhat.com> # vfio-related parts
Acked-by: Logan Gunthorpe <logang@deltatee.com> # switchtec
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Diffstat (limited to 'Documentation/nvmem')
-rw-r--r-- | Documentation/nvmem/nvmem.rst | 189 |
1 files changed, 0 insertions, 189 deletions
diff --git a/Documentation/nvmem/nvmem.rst b/Documentation/nvmem/nvmem.rst deleted file mode 100644 index 3866b6e066d5..000000000000 --- a/Documentation/nvmem/nvmem.rst +++ /dev/null @@ -1,189 +0,0 @@ -:orphan: - -=============== -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(). - -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); - -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 -===================================== - -When a consumer no longer needs the NVMEM, it has to release the reference -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 |