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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	tun-
     able 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 ker-
				   nel.
     /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	13.0		       November	19, 2019		  FreeBSD 13.0
NAME | DESCRIPTION | DEVICE HINTS | FILES | EXAMPLES | SEE ALSO | HISTORY

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