freebsd-dev/share/man/man9/nvmem.9
Emmanuel Vadot cfe196fbed nvmem: Add nvmem interface and helpers
The nvmem interface helps provider of nvmem data to expose themselves to consumer.
NVMEM is generally present on some embedded board in a form of eeprom or fuses.
The nvmem api are helpers for consumer to read/write the cell data from a provider.

Differential Revision:	https://reviews.freebsd.org/D16419
2018-07-31 19:08:24 +00:00

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.\" Copyright (c) 2018 Emmanuel Vadot <manu@freebsd.org>
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.Dd July 24, 2018
.Dt nvmem 9
.Os
.Sh NAME
.Nm nvmem
.Nm nvmem_get_cell_len ,
.Nm nvmem_read_cell_by_name ,
.Nm nvmem_read_cell_by_idx ,
.Nm nvmem_write_cell_by_name ,
.Nm nvmem_write_cell_by_idx ,
.Sh SYNOPSIS
.Cd "options EXT_RESOURCES"
.Cd "options FDT"
.Cd "device nvmem"
.In sys/extres/nvmem/nvmem.h
.Ft int
.Fn nvmem_get_cell_len "phandle_t node" "const char *name"
.Ft int
.Fn nvmem_read_cell_by_name "phandle_t node" "const char *name" "void *cell" "size_t buflen"
.Ft int
.Fn nvmem_read_cell_by_idx "phandle_t node" "int idx" "void *cell" "size_t buflen"
.Ft int
.Fn nvmem_write_cell_by_name "phandle_t node" "const char *name" "void *cell" "size_t buflen"
.Ft int
.Fn nvmem_write_cell_by_idx "phandle_t node" "int idx" "void *cell" "size_t buflen"
.Sh 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.
.Pp
The
.Nm
API consist of helpers functions for consumer and device methods for
providers.
.Sh FUNCTIONS
.Bl -tag -width indent
.It Fn 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
.It Fn 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 sucess or ENOENT if the cell doesn't exists, ENXIO if no provider device was found,
EINVAL if the size isn't correct.
.It Fn 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 sucess or ENOENT if the cell doesn't exists, ENXIO if no provider device was found,
EINVAL if the size isn't correct.
.It Fn 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 sucess or ENOENT if the cell doesn't exists, ENXIO if no provider device was found,
EINVAL if the size isn't correct.
.It Fn 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 sucess or ENOENT if the cell doesn't exists, ENXIO if no provider device was found,
EINVAL if the size isn't correct.
.El
.Sh DEVICE METHODS
.Bl -tag -width indent
.It Fn nvmem_read "device_t dev" "uint32_t offset" "uint32_t size" "uint8_t *buffer"
Provider device method to read a cell content.
.It Fn nvmem_write "device_t dev" "uint32_t offset" "uint32_t size" "uint8_t *buffer"
Provider device method to write a cell content.
.El
.Sh EXAMPLES
Consider this DTS
.Bd -literal
/* Provider */
eeprom: eeprom@20000 {
board_id: id@0 {
reg = <0x0 0x4>;
};
};
/* Consumer */
device@30000 {
...
nvmem-cells = <&board_id>
nvmem-cell-names = "boardid";
};
.Ed
.Pp
The device driver for eeprom@20000 needs to expose itself as a provider
.Bd -literal
#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
};
.Ed
.Pp
The consumer device driver for device@30000 can now read the nvmem data
.Bd -literal
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));
...
}
.Ed
.Sh HISTORY
The nvmem related function first appear in
.Fx 12.0 .
The nvmem interface and manual page was written by
.An Emmanuel Vadot Aq Mt manu@FreeBSD.org .