.\" Copyright (c) 2001
.\" Kazutaka YOKOTA <yokota@zodiac.mech.utsunomiya-u.ac.jp>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
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.\"    the first lines of this file unmodified.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
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.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" $FreeBSD$
.\"
.Dd July 23, 2015
.Dt DEVICE.HINTS 5
.Os
.Sh NAME
.Nm device.hints
.Nd device resource hints
.Sh DESCRIPTION
The
.Nm
file is read in by the boot
.Xr loader 8
when the system is about to start, and its contents are
passed to the kernel.
It contains various variables to control the boot behavior of
the kernel.
These variables are typically
.Dq device hints ,
but can include any kernel tunable values.
.Pp
The file contains one variable per line.
Lines starting with the
.Ql #
character are comments and are ignored by the boot loader.
.Pp
After the file is read by the boot loader, you may examine
the variables with the
.Ic show
command, and may add a new variable, modify an existing one,
or delete a variable with the
.Ic set
and
.Ic unset
commands of the boot loader
(see
.Xr loader 8 ) .
.Pp
After the system has started, you can dump these variables
with the
.Xr kenv 1
command.
.Sh DEVICE HINTS
Device hint variables are used by device drivers to set up
the device.
They are most often used by ISA device drivers to specify
where the driver will probe for the relevant devices, and what
resources it will attempt to use.
.Pp
A device hint line looks like:
.Pp
.Sm off
.D1 Li hint. Ar driver . Ar unit . Ar keyword Li = Qq Ar value
.Sm on
.Pp
where
.Ar driver
is the name of a device driver,
.Ar unit
is the unit number, and
.Ar keyword
is the keyword of the hint.
The keyword may be:
.Pp
.Bl -tag -width ".Li disabled" -compact -offset indent
.It Li at
specifies a bus to which the device is attached.
.It Li port
specifies the start address of I/O ports to be used by the device.
.It Li portsize
specifies the number of ports used by the device.
.It Li irq
is the interrupt line number to be used.
.It Li drq
is the DMA channel number.
.It Li maddr
specifies the physical memory address used by the device.
.It Li msize
specifies the physical memory size used by the device.
.It Li flags
sets various flag bits for the device.
.It Li disabled
can be set to
.Qq 1
to disable the device.
.El
.Pp
A device driver may require one or more hint lines with these keywords,
and may accept other keywords not listed here, through
.Xr resource_int_value 9 .
Consult individual device drivers' manual pages for available
keywords and their possible values.
.\" .Sh CONTROL VARIABLES
.\" Lines not starting with
.\" .Dq hint.
.\" specify other control variables for the kernel.
.\" They look:
.\" .Pp
.\" .Dl <name>="<value>"
.\" XXX
.\" WE SHOULD LIST AVAILABLE VARIABLE NAMES AND THEIR POSSIBLE VALUES HERE!
.\" .Pp
.Sh FILES
.Bl -tag -width ".Pa /sys/ Ns Ar ARCH Ns Pa /conf/GENERIC.hints" -compact
.It Pa /boot/device.hints
Device resource hints file.
.It Pa /sys/ Ns Ar ARCH Ns Pa /conf/GENERIC.hints
Sample resource hints for the
.Pa GENERIC
kernel.
.It Pa /sys/ Ns Ar ARCH Ns Pa /conf/NOTES
Notes on the kernel configuration file and device resource hints.
.El
.Sh EXAMPLES
The following example sets up resources for the
.Xr sio 4
driver on the ISA bus:
.Bd -literal -offset indent
hint.sio.0.at="isa"
hint.sio.0.port="0x3F8"
hint.sio.0.flags="0x10"
hint.sio.0.irq="4"
.Ed
.Pp
The following example disables the ACPI driver:
.Bd -literal -offset indent
hint.acpi.0.disabled="1"
.Ed
.Pp
Setting a tunable variable:
.Bd -literal -offset indent
vm.pmap.pg_ps_enabled=1
.Ed
.Sh SEE ALSO
.Xr kenv 1 ,
.Xr loader.conf 5 ,
.Xr loader 8 ,
.Xr resource_int_value 9
.Sh HISTORY
The
.Nm
file first appeared in
.Fx 5.0 .