gpiobus — GPIO bus system

       This manual page was written by Sean Bruno <sbruno@FreeBSD.org>.

Debian                                            June 27, 2019                                          GPIO(4)

       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_sethint.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.

       The gpiobus manual page first appeared in FreeBSD 10.0.

       gpiobus — GPIO bus system

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

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

             devicegpiodevicegpiocdevicegpioiicdevicegpioled

       Additional device entries for the ARM architecture include:

             devicea10_gpiodevicebcm_gpiodeviceimx51_gpiodevicelpcgpiodevicemv_gpiodeviceti_gpiodevicegpio_aviladevicegpio_cambriadevicezy7_gpiodevicepxagpio

       Additional device entries for the MIPS architecture include:

             devicear71xxx_gpiodeviceocteon_gpiodevicert305_gpio

       Additional device entries for the POWERPC architecture include:

             devicewiigpiodevicemacgpio