gpio(4) manual page

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.

Manual Pages — GPIO

NAME

CONTENTS

SYNOPSIS

DESCRIPTION

SEE ALSO

HISTORY

AUTHORS

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.

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.