GPIO

Introduction to the functions and usage of GPIO.

Module Introduction

GPIO is the controller that manages the gpio module.

Function Introduction

The Linux gpio subsystem driver framework mainly consists of three parts:

• GPIO controller driver: Interacts with the GPIO controller, initializes and operates the controller
• gpio lib driver: Provides standard APIs for other modules, such as setting GPIO direction, reading and writing GPIO level state
• GPIO character device driver: Reports GPIO as character devices to user space, user space can access GPIO through standard file interfaces

Source Code Structure Introduction

The controller driver code is under the drivers/gpio directory:

|-- gpio-k1x.c  

Key Features

Feature	Description
Supports direction setting	Supports setting GPIO as input or output
Supports output high/low level setting	Supports setting GPIO level in output mode
Supports gpio interrupt function	Supports rising and falling edge triggered gpio interrupts

Configuration Introduction

Mainly includes driver CONFIG enable configuration and dts configuration

CONFIG Configuration

CONFIG_GPIOLIB provides support for the gpio controller. By default, this option is Y.

Device Drivers
        GPIO Support (GPIOLIB [=y])

CONFIG_GPIO_K1X provides support for the k1 gpio controller. By default, this option is Y.

Device Drivers  
        GPIO Support (GPIOLIB [=y])
                Virtual GPIO drivers  
                        SPACEMIT-K1X GPIO support (GPIO_K1X [=y])

Usage Introduction

The solution's gpio usage is divided into 3 steps.

1. Description of the gpio used in the solution
2. Setting the corresponding pin
3. Usage of gpio

Notes:

1. Pin numbers are defined in the kernel directory: include\dt-bindings\pinctrl\k1-x-pinctrl.h.
2. The same pin configuration means that a group of pins are set to gpio function with the same configuration, i.e., mux mode, pull-up/pull-down, edge detection, and drive strength are the same.

Solution gpio Description

Used to describe all the gpio used in the solution.

Defined using the linux gpio framework gpio-ranges property. If a segment of gpio corresponds to consecutive pin numbers, it is defined as a group.

Example solution dts file gpio controller definition

&gpio{
        gpio-ranges = <
                &pinctrl 49  GPIO_49  2
                &pinctrl 58  GPIO_58  1
                &pinctrl 63  GPIO_63  5
                &pinctrl 70  PRI_TDI  4
                &pinctrl 74  GPIO_74  1
                &pinctrl 80  GPIO_80  4
                &pinctrl 90  GPIO_90  3
                &pinctrl 96  DVL0     2
                &pinctrl 110 GPIO_110 1
                &pinctrl 114 GPIO_114 3
                &pinctrl 123 GPIO_123 5
        >;
};

gpio pin configuration

Set the pins corresponding to the gpio used in the solution to gpio function and configure (edge detection/pull-up/pull-down/drive strength).

Set using the pinctrl-single,gpio-range property. If there is a segment of consecutive pin numbers with the same configuration, configure as a group.

For pin configuration parameters, refer to pin configuration parameters.

Example:

&pinctrl {
        pinctrl-single,gpio-range = <
                &range GPIO_49  2 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_3V_DS4)
                &range GPIO_58  1 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_63  2 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_65  1 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range GPIO_66  2 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_3V_DS4)
                &range PRI_TDI  2 (MUX_MODE1 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range PRI_TCK  1 (MUX_MODE1 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range PRI_TDO  1 (MUX_MODE1 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range GPIO_74  1 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range GPIO_80  1 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_3V_DS4)
                &range GPIO_81  3 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range GPIO_90  1 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_91  2 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range DVL0     2 (MUX_MODE1 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_110 1 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_114 1 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_115 1 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_116 1 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range GPIO_123 1 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
                &range GPIO_124 1 (MUX_MODE0 | EDGE_NONE | PULL_UP   | PAD_1V8_DS2)
                &range GPIO_125 3 (MUX_MODE0 | EDGE_NONE | PULL_DOWN | PAD_1V8_DS2)
        >;
};

gpio Usage

If the solution eth0 uses gpio 110 as the phy reset signal, then eth0 uses gpio 110 as follows.

&eth0 {
    emac,reset-gpio = <&gpio 110 0>;
};

API Introduction

API Introduction

Request a specified gpio

int gpio_request(unsigned gpio, const char *label);

Free a requested gpio

void gpio_free(unsigned gpio);

Set the specified GPIO as input mode

int gpio_direction_input(unsigned gpio)

Set the specified GPIO as output mode and initial value

int gpio_direction_output(unsigned gpio, int value)

Set the output value of the specified GPIO

void gpio_set_value(unsigned gpio, int value)

Get the signal value of the specified GPIO

int gpio_get_value(unsigned gpio)

Get the interrupt number corresponding to the specified gpio

int gpio_to_irq(unsigned gpio)

Debug Introduction

sysfs

Read and operate GPIO ports

/sys/class/gpio
|-- export
|-- gpiochip0 -> ../../devices/gpiochip0/gpio/gpiochip0
|-- gpiochip512 -> ../../devices/platform/soc/d401d800.i2c/i2c-8/8-0041/spacemit-pinctrl@spm8821/gpio/gpiochip512
`-- unexport

• export
  Used to notify the system to export the GPIO pin number to be controlled
• unexport
  Used to notify the system to unexport
• gpiochipX
  Detailed information of gpio X
• gpioX/direction
  Direction of gpio X
• gpioX/value
  Port value of gpio X

debugfs

Displays the gpio controllers in the system and the gpio information they manage.

/sys/kernel/debug/gpio
# cat gpio
gpiochip0: GPIOs 0-127, k1x-gpio:
 gpio-63  (                    |reset               ) out lo
 gpio-67  (                    |pwr                 ) out hi
 gpio-80  (                    |cd                  ) in  hi ACTIVE LOW
 gpio-96  (                    |sys-led             ) out lo
 gpio-97  (                    |vbus                ) out hi
 gpio-110 (                    |mdio-reset          ) out hi
 gpio-111 (                    |reset               ) out lo
 gpio-113 (                    |pwdn                ) out lo
 gpio-115 (                    |mdio-reset          ) out hi
 gpio-116 (                    |regon               ) out hi
 gpio-123 (                    |hub                 ) out hi
 gpio-124 (                    |hub                 ) out hi
 gpio-127 (                    |?                   ) out lo

gpiochip1: GPIOs 512-517, parent: platform/spacemit-pinctrl@spm8821, spacemit-pinctrl@spm8821, can sleep:

Test Introduction

Check whether the gpio setting is correct by viewing the register value corresponding to the gpio

devmem reg_addr

FAQ