$ make CROSS_COMPILE=arm-none-linux-gnueabi- ARCH=arm menuconfig

• Select Device Drivers from the main menu.

    Power management options  --- >
[*] Networking support  --- >
    Device Drivers  --- >
    File systems  --- >
...
...

• Select GPIO Support from the menu.

    PPS support  --- >
    PTP clock support  --- >
-*- GPIO Support  --- >
< > Dallas's 1-wire support  --- >
...
...

Sysfs entries configuration

[ ] Debug GPIO calls
[*] /sys/class/gpio/... (sysfs interface)
    *** Memory mapped GPIO drivers: ***
< > Basic memory-mapped GPIO controllers support
...
...

• After doing driver selection, exit and save the kernel configuration when prompted.

IRQ handling

• Map GPIO number to corresponding IRQ number, GPIO 0 need not use IRQ 0

irq_num = gpio_to_irq(30)

• Request IRQ, make sure that irq_num should be non-error value

request_irq(irq_num, handler, 0, "gpio_test", NULL);

• Set IRQ type Raising/Falling/Level triggered

set_irq_type(irq_num, IRQ_TYPE_EDGE_RISING);

• During the clean-up path free the IRQ and gpio

free_irq(irq_num, NULL);
gpio_free(30);

Driver Usage

Kernel Level

• Allocate memory to GPIO line, can be achieved by doing gpio_request()

err = gpio_request(30, "sample_name");

• Depending on the requirement set GPIO as input or output pin then set gpio value as high or low.

gpio_direction_input(30);

gpio_direction_output(30, 1);

gpio_export(30, true);

gpio_get_value(30);

User Space - Sysfs control

• Enable GPIO sysfs support in kernel configuration and build the kernel

Device Drivers  --- > GPIO Support  --- > /sys/class/gpio/... (sysfs interface)

• Sysfs entries

Export the particular GPIO pin for user control. GPIO30 is taken as example.

$ echo 30 > /sys/class/gpio/export

Change the GPIO pin direction to in/out

$ echo "out" > /sys/class/gpio/gpio30/direction

$ echo "in" > /sys/class/gpio/gpio30/direction

Change the value

$ echo 1 > /sys/class/gpio/gpio30/value

$ echo 0 > /sys/class/gpio/gpio30/value

Unexport the GPIO pin

$ echo 30 > /sys/class/gpio/unexport

$ mount -t debugfs debugfs /sys/kernel/debug

$ cat /sys/kernel/debug/gpio

最後這個是重點!  因為有些driver 沒按照devicetree 架構寫 而是在驅動內自行設定GPIO 所以有時須要看一下哪些IO已經被要走了! 避免devicetree 寫半天 但還是有問題的狀況

# cat /sys/kernel/debug/gpio
GPIOs 0-31, platform/pinctrl, gpio0:
 gpio-1   (                    |vcc_sd              ) out lo
 gpio-4   (                    |bt_default_wake_host) out hi
 gpio-5   (                    |GPIO Key Power      ) in  hi
 gpio-8   (                    |cx20921 rstn        ) out hi
 gpio-9   (                    |bt_default_reset    ) out hi
 gpio-10  (                    |reset               ) out hi
 gpio-11  (                    |SPK_EN              ) out hi

GPIOs 32-63, platform/pinctrl, gpio1:
 gpio-33  (                    |vbus-5v             ) out lo
 gpio-34  (                    |int-n               ) in  hi
 gpio-45  (                    |enable              ) out lo
 gpio-46  (                    |vsel                ) out lo
 gpio-49  (                    |vsel                ) out lo

GPIOs 64-95, platform/pinctrl, gpio2:
 gpio-83  (                    |bt_default_rts      ) out lo
 gpio-90  (                    |bt_default_wake     ) out hi
 gpio-92  (                    |WLAN_PEN            ) out lo

GPIOs 96-127, platform/pinctrl, gpio3:
 gpio-111 (                    |mdio-reset          ) out hi

GPIOs 128-159, platform/pinctrl, gpio4:
 gpio-149 (                    |AUDIO_GPIO          ) out hi
 gpio-150 (                    |wdt87xx_Reset_Pin   ) out hi
 gpio-153 (                    |vcc5v0_host         ) out hi
 gpio-157 (                    |enable              ) out lo
 gpio-158 (                    |enable              ) out hi