.\" Copyright (c) 2018 Emmanuel Vadot <manu@freebsd.org>
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.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 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 .