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.Dd June 27, 2019
.Dt GPIO 4
.Os
.Sh NAME
.Nm gpiobus
.Nd GPIO bus system
.Sh SYNOPSIS
To compile these devices into your kernel and use the device hints, place the
following lines in your kernel configuration file:
.Bd -ragged -offset indent
.Cd "device gpio"
.Cd "device gpioc"
.Cd "device gpioiic"
.Cd "device gpioled"
.Ed
.Pp
Additional device entries for the
.Li ARM
architecture include:
.Bd -ragged -offset indent
.Cd "device a10_gpio"
.Cd "device bcm_gpio"
.Cd "device imx51_gpio"
.Cd "device lpcgpio"
.Cd "device mv_gpio"
.Cd "device ti_gpio"
.Cd "device gpio_avila"
.Cd "device gpio_cambria"
.Cd "device zy7_gpio"
.Cd "device pxagpio"
.Ed
.Pp
Additional device entries for the
.Li MIPS
architecture include:
.Bd -ragged -offset indent
.Cd "device ar71xxx_gpio"
.Cd "device octeon_gpio"
.Cd "device rt305_gpio"
.Ed
.Pp
Additional device entries for the
.Li POWERPC
architecture include:
.Bd -ragged -offset indent
.Cd "device wiigpio"
.Cd "device macgpio"
.Ed
.Sh DESCRIPTION
The
.Nm
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.
.Pp
The acronym
.Li GPIO
means
.Dq General-Purpose Input/Output.
.Pp
The BUS physically consists of multiple pins that can be configured
for input/output, IRQ delivery, SDA/SCL
.Em iicbus
use, etc.
.Pp
On some embedded architectures (like MIPS), discovery of the bus and
configuration of the pins is done via
.Xr device.hints 5
in the platform's kernel
.Xr config 5
file.
.Pp
On some others (like ARM), where
.Xr 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.
.Pp
On a
.Xr device.hints 5
based system these hints can be used to configure drivers for devices
attached to
.Nm
pins:
.Bl -tag -width ".Va hint.driver.unit.pin_list"
.It Va hint.driver.unit.at
The
.Nm gpiobus
where the device is attached.
For example,
.Qq gpiobus0 .
.Ar driver
and
.Ar unit
are the driver name and the unit number for the device driver.
.It Va hint.driver.unit.pins
This is a bitmask of the pins on the
.Nm 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.
.It Va hint.driver.unit.pin_list
This is a list of pin numbers of pins on the
.Nm 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
.Ar 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.
.El
.Pp
The following
.Xr device.hints 5
are only provided by the
.Cd ar71xx_gpio
driver:
.Bl -tag -width ".Va hint.gpio.function_clear"
.It Va 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.
.It Va 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.
.It Va hint.gpio.function_set
.It Va 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.
.El
.Pp
Simply put, each pin of the GPIO interface is connected to an input/output
of some device in a system.
.Sh SEE ALSO
.Xr gpioiic 4 ,
.Xr gpioled 4 ,
.Xr iicbus 4 ,
.Xr device.hints 5 ,
.Xr gpioctl 8
.Sh HISTORY
The
.Nm
manual page first appeared in
.Fx 10.0 .
.Sh AUTHORS
This
manual page was written by
.An Sean Bruno Aq Mt sbruno@FreeBSD.org .
