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     gpiobus — GPIO bus system


     To compile these devices into your kernel and use the device hints, place the following
     lines in your kernel configuration file:

           device gpio
           device gpioc
           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


     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:        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


     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.


     gpioiic(4), gpioled(4), iicbus(4), device.hints(5), gpioctl(8)


     The gpiobus manual page first appeared in FreeBSD 10.0.


     This manual page was written by Sean Bruno <>.