GPIO(4) FreeBSD Kernel Interfaces Manual GPIO(4)
NAME
gpiobus - GPIO bus system
SYNOPSIS
To compile these devices into your kernel and use the device hints, place
the following lines in your kernel configuration file:
device gpio
device gpioiic
device gpioled
Additional device entries for the ARM architecture include:
device a10_gpio
device bcm_gpio
device imx51_gpio
device lpcgpio
device mv_gpio
device ti_gpio
device gpio_avila
device gpio_cambria
device zy7_gpio
device pxagpio
Additional device entries for the MIPS architecture include:
device ar71xxx_gpio
device octeon_gpio
device rt305_gpio
Additional device entries for the POWERPC architecture include:
device wiigpio
device macgpio
Additional device entries for the RISC-V architecture include:
device sifive_gpio
DESCRIPTION
The gpiobus system provides a simple interface to the GPIO pins that are
usually available on embedded architectures and can provide bit banging
style devices to the system.
The acronym GPIO means "General-Purpose Input/Output."
The BUS physically consists of multiple pins that can be configured for
input/output, IRQ delivery, SDA/SCL iicbus use, etc.
On some embedded architectures (like MIPS), discovery of the bus and
configuration of the pins is done via device.hints(5) in the platform's
kernel config(5) file.
On some others (like ARM), where FDT(4) is used to describe the device
tree, the bus discovery is done via the DTS passed to the kernel, being
either statically compiled in, or by a variety of ways where the boot
loader (or Open Firmware enabled system) passes the DTS blob to the
kernel at boot.
On a device.hints(5) based system these hints can be used to configure
drivers for devices attached to gpiobus pins:
hint.driver.unit.at The gpiobus where the device is attached. For
example, "gpiobus0". driver and unit are the
driver name and the unit number for the device
driver.
hint.driver.unit.pins This is a bitmask of the pins on the gpiobus
that are connected to the device. The pins
will be allocated to the specified driver
instance. Only pins with numbers from 0 to 31
can be specified using this hint.
hint.driver.unit.pin_list This is a list of pin numbers of pins on the
gpiobus that are connected to the device. The
pins will be allocated to the specified driver
instance. This is a more user friendly
alternative to the pins hint. Additionally,
this hint allows specifying pin numbers
greater than 31. The numbers can be decimal
or hexadecimal with 0x prefix. Any non-digit
character can be used as a separator. For
example, it can be a comma, a slash or a
space. The separator can be followed by any
number of space characters.
The following device.hints(5) are only provided by the ar71xx_gpio
driver:
hint.gpio.%d.pinmask This is a bitmask of pins on the GPIO board
that we would like to expose for use to the
host operating system. To expose pin 0, 4 and
7, use the bitmask of 10010001 converted to the
hexadecimal value 0x0091.
hint.gpio.%d.pinon This is a bitmask of pins on the GPIO board
that will be set to ON at host start. To set
pin 2, 5 and 13 to be set ON at boot, use the
bitmask of 10000000010010 converted to the
hexadecimal value 0x2012.
hint.gpio.function_set
hint.gpio.function_clear These are bitmasks of pins that will remap a
pin to handle a specific function (USB, UART
TX/RX, etc) in the Atheros function registers.
This is mainly used to set/clear functions that
we need when they are set up or not set up by
uBoot.
Simply put, each pin of the GPIO interface is connected to an
input/output of some device in a system.
SEE ALSO
gpioiic(4), gpioled(4), iicbus(4), device.hints(5), gpioctl(8)
HISTORY
The gpiobus manual page first appeared in FreeBSD 10.0.
AUTHORS
This manual page was written by Sean Bruno <sbruno@FreeBSD.org>.
FreeBSD 15.1-STABLE-HBSD August 28, 2025 GPIO(4)