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.\" Copyright (c) 2019 Rajesh Kumar <rajesh1.kumar@amd.com>
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.Dd August 29, 2019
.Dt NTB_HW_AMD 4
.Os
.Sh NAME
.Nm ntb_hw_amd
.Nd AMD Non-Transparent Bridge driver
.Sh SYNOPSIS
To compile this driver into your kernel,
place the following lines in your kernel configuration file:
.Bd -ragged -offset indent
.Cd "device ntb"
.Cd "device ntb_hw_amd"
.Ed
.Pp
Or, to load the driver as a module at boot, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
ntb_hw_amd_load="YES"
.Ed
.Pp
The following sysctls are supported in this driver
.Bl -ohang
.It Va dev.ntb_hw.X.info
Reading this sysctl will give the basic details like the number of memory
windows, scratchpads and doorbells exposed by the NTB on the local host to
access the devices beyond the bridge.
It also provides details about the masked doorbells, translation address and
size limit of each exposed memory window and link status information.
.El
.Sh DESCRIPTION
The
.Nm ntb_hw_amd
driver provides support for the Non-Transparent Bridge (NTB) hardware in
AMD EPYC processor family.
The Non-Transparent Bridge does not look as a regular PCI bridge, but as PCI
endpoint device, hiding the devices behind it.
The driver hides details of hardware on the other side, but exposes memory windows,
scratchpads and doorbells to access the other side via hardware independent
KPI to
.Xr ntb 4
subsystem.
.Pp
The hardware provides 2 (both 64-bit) or 3 (one 32-bit and two 64-bit) memory
windows to the other system's memory, up to 16 scratchpad registers and 16
doorbells to communicate with and interrupt the other system respectively.
.Sh CONFIGURATION
The NTB configuration should be set by BIOS.
This includes enabling NTB, choosing topology (only NTB-to-Root Port
mode is supported now), role of the host in the topology.
This needs to be done on both systems.
.Pp
The BAR size for memory windows is configured to 1 MiB by default.
.Sh SEE ALSO
.Xr if_ntb 4 ,
.Xr ntb 4 ,
.Xr ntb_transport 4
.Sh AUTHORS
.An -nosplit
The
.Nm
driver was developed by AMD and originally written by
.An Rajesh Kumar Aq Mt rajesh1.kumar@amd.com .
Reviewed by
.An Alexander Motin Aq Mt mav@FreeBSD.org ,
.An Conrad E. Meyer Aq Mt cem@FreeBSD.org
and
.An Warner Losh Aq Mt imp@FreeBSD.org .