DEVICE.HINTS(5)           FreeBSD File Formats Manual          DEVICE.HINTS(5)

NAME
     device.hints - device resource hints

DESCRIPTION
     The device.hints file is read in by the boot 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 "device hints", but can include any kernel
     tunable values.

     The file contains one variable per line.  Lines starting with the `#'
     character are comments and are ignored by the boot loader.

     After the file is read by the boot loader, you may examine the variables
     with the show command, and may add a new variable, modify an existing
     one, or delete a variable with the set and unset commands of the boot
     loader (see loader(8)).

     After the system has started, you can dump these variables with the
     kenv(1) command.

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.

     A device hint line looks like:

           hint.driver.unit.keyword="value"

     where driver is the name of a device driver, unit is the unit number, and
     keyword is the keyword of the hint.  The keyword may be:

           at            specifies a bus to which the device is attached.
           port          specifies the start address of I/O ports to be used
                         by the device.
           portsize      specifies the number of ports used by the device.
           irq           is the interrupt line number to be used.
           drq           is the DMA channel number.
           maddr         specifies the physical memory address used by the
                         device.
           msize         specifies the physical memory size used by the
                         device.
           flags         sets various flag bits for the device.
           disabled      can be set to "1" to disable the device.

     A device driver may require one or more hint lines with these keywords,
     and may accept other keywords not listed here, through
     resource_int_value(9).  Consult individual device drivers' manual pages
     for available keywords and their possible values.

FILES
     /boot/device.hints                              Device resource hints
                                                     file.
     /sys/ARCH/conf/GENERIC.hints                    Sample resource hints for
                                                     the GENERIC kernel.
     /sys/ARCH/conf/NOTES                            Notes on the kernel
                                                     configuration file and
                                                     device resource hints.

EXAMPLES
     The following example sets up resources for the uart(4) driver on the ISA
     bus:

           hint.uart.0.at="isa"
           hint.uart.0.port="0x3F8"
           hint.uart.0.flags="0x10"
           hint.uart.0.irq="4"

     The following example disables the ACPI driver:

           hint.acpi.0.disabled="1"

     Setting a tunable variable:

           vm.pmap.pg_ps_enabled=1

SEE ALSO
     kenv(1), loader.conf(5), loader(8), resource_int_value(9)

HISTORY
     The device.hints file first appeared in FreeBSD 5.0.

FreeBSD 13.1-RELEASE-p6        November 19, 2019       FreeBSD 13.1-RELEASE-p6