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.\" This documentation was written by
.\" Konstantin Belousov <kib@FreeBSD.org> under sponsorship
.\" from the FreeBSD Foundation.
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.Dd September 5, 2019
.Dt NVDIMM 4
.Os
.Sh NAME
.Nm nvdimm
.Nd ACPI NVDIMM driver
.Sh SYNOPSIS
To load the driver as a module at boot, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
nvdimm_load="YES"
.Ed
.Sh DESCRIPTION
.Bf -symbolic
Note:
The
.Nm
driver is under development and has some important limitations
described below.
.Ef
.Pp
The
.Nm
driver provides access to Non-Volatile DIMM (NVDIMM) persistent memory
devices, which are ACPI-enumerated under the root NVDIMM device
with a
.Va _HID
of
.Dv ACPI0012
and in the
.Dv NFIT
table.
.Pp
For each System Physical Address (SPA) Range described by NFIT, a
device node
.Pa /dev/nvdimm_spaNNN
is created, where
.Dv NNN
is the SPA position in the table.
The node can be used to
.Xr read 2 ,
.Xr write 2 ,
or
.Xr mmap 2
the device.
.Pp
Also, for each SPA, the geom provider
.Pa spaNNN
is created, which can be used to create a conventional filesystem (e.g.,
by
.Xr newfs 8 )
and
.Xr mount 8
it as any storage volume.
Content accessible by
.Pa /dev/nvdimm_spaNNN
and
.Pa /dev/spaNNN
is coherent.
.Pp
The
.Nm
driver has support for reading NVDIMM namespaces (if supported by your
hardware and already configured by some other mechanism, e.g., a BIOS
configuration screen).
The driver will provide a
.Pa /dev/nvdimm_spaNNNnsMMM
device node and
.Pa spaNNNnsMMM
geom provider for each namespace in a SPA, which behave analogously to their
full-SPA cousins described above.
.Sh SEE ALSO
.Xr acpi 4 ,
.Xr GEOM 4 ,
.Xr geom 8 ,
.Xr mount 8 ,
.Xr newfs 8 ,
.Xr disk 9
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 12.0 .
.Sh AUTHORS
.An -nosplit
The
.Nm
driver was originally written by
.An Konstantin Belousov Aq Mt kib@FreeBSD.org ,
and then updated by
.An D. Scott Phillips Aq Mt scottph@FreeBSD.org .
.Sh BUGS
The
.Nm
driver does not utilize the Block Window interface, so if a write to an
NVDIMM is interrupted due to a system crash or power outage,
the corresponding page might be left in a partially updated state.
.Pp
There is no support for Device-Specific Methods (DSM), used to report and
control device health and wearing.
.Pp
The driver depends on the
.Xr pmap_largemap 9
pmap interface, which is currently only implemented on amd64.
The interface can be only reasonable implemented on 64bit architectures.