要能使用/sys/class/gpio就要先開啟相關kernel config如下, 如提示所說, 該ABI已經棄用, 改由character device /dev/gpiochipN取代, 不過這裡還是會簡單交代一下相關資訊, 作為紀錄.
│ CONFIG_GPIO_SYSFS: │ │ │ │ Say Y here to add the legacy sysfs interface for GPIOs. │ │ │ │ This ABI is deprecated. If you want to use GPIO from userspace, │ │ use the character device /dev/gpiochipN with the appropriate │ │ ioctl() operations instead. The character device is always │ │ available. │ │ │ │ Symbol: GPIO_SYSFS [=y] │ │ Type : bool │ │ Prompt: /sys/class/gpio/... (sysfs interface) │ │ Location: │ │ -> Device Drivers │ │ -> GPIO Support (GPIOLIB [=y]) │ │ Defined at drivers/gpio/Kconfig:61 │ │ Depends on: GPIOLIB [=y] && SYSFS [=y] │
在設定玩kernel config之後, 重新編譯kernel, 就可以看見"/sys/class/gpio"目錄, 裡面幾個重要的檔案,
| export | Userspace may ask the kernel to export control of a GPIO to userspace by writing its number to this file. |
| unexport | Reverses the effect of exporting to userspace. |
"echo 19 > /sys/class/gpio/export" 後, 目錄/sys/class/gpio/gpio19/就會被創建出來, 裡面會包含
| direction | reads as either "in" or "out" |
| value | reads as either 0 (low) or 1 (high) |
| edge | reads as either "none", "rising", "falling", or "both" |
| active_low | reads as either 0 (false) or 1 (true) |
此外還可以透過debugfs來檢查當前的GPIO設定
/ # cat /sys/kernel/debug/gpio gpiochip3: GPIOs 499-499, parent: platform/basic-mmio-gpio.3.auto, sys_flash: gpiochip2: GPIOs 500-501, parent: platform/basic-mmio-gpio.2.auto, sys_mci: gpio-500 ( |cd ) in lo gpio-501 ( |wp ) in lo gpiochip1: GPIOs 502-509, parent: platform/basic-mmio-gpio.1.auto, sys_led: gpio-502 ( |? ) out lo gpio-503 ( |? ) out lo gpio-504 ( |? ) out lo gpio-505 ( |? ) out lo gpio-506 ( |? ) out hi gpio-507 ( |? ) out lo gpio-508 ( |? ) out lo gpio-509 ( |? ) out lo gpiochip0: GPIOs 510-511, parent: platform/10000000.sysreg, 10000000.sysreg: / # ls -al /sys/class/gpio/ total 0 drwxr-xr-x 2 0 0 0 Jan 3 00:40 . drwxr-xr-x 36 0 0 0 Jan 3 00:40 .. --w------- 1 0 0 4096 Jan 3 00:40 export lrwxrwxrwx 1 0 0 0 Jan 3 00:40 gpiochip499 -> ../../devices/platform/10000000.sysreg/basic-mmio-gpio.3.auto/gpio/gpiochip499 lrwxrwxrwx 1 0 0 0 Jan 3 00:40 gpiochip500 -> ../../devices/platform/10000000.sysreg/basic-mmio-gpio.2.auto/gpio/gpiochip500 lrwxrwxrwx 1 0 0 0 Jan 3 00:40 gpiochip502 -> ../../devices/platform/10000000.sysreg/basic-mmio-gpio.1.auto/gpio/gpiochip502 lrwxrwxrwx 1 0 0 0 Jan 3 00:40 gpiochip510 -> ../../devices/platform/10000000.sysreg/gpio/gpiochip510 --w------- 1 0 0 4096 Jan 3 00:40 unexport
接下來export 510, 511, 然後在unexport 511, 設定510, 相關操作如下
/ # echo 510 > /sys/class/gpio/export / # echo 511 > /sys/class/gpio/export / # ls -al /sys/class/gpio/ total 0 drwxr-xr-x 2 0 0 0 Jan 3 00:40 . drwxr-xr-x 36 0 0 0 Jan 3 00:40 .. --w------- 1 0 0 4096 Jan 3 00:43 export lrwxrwxrwx 1 0 0 0 Jan 3 00:42 gpio510 -> ../../devices/platform/10000000.sysreg/gpiochip0/gpio/gpio510 lrwxrwxrwx 1 0 0 0 Jan 3 00:43 gpio511 -> ../../devices/platform/10000000.sysreg/gpiochip0/gpio/gpio511 lrwxrwxrwx 1 0 0 0 Jan 3 00:40 gpiochip499 -> ../../devices/platform/10000000.sysreg/basic-mmio-gpio.3.auto/gpio/gpiochip499 lrwxrwxrwx 1 0 0 0 Jan 3 00:40 gpiochip500 -> ../../devices/platform/10000000.sysreg/basic-mmio-gpio.2.auto/gpio/gpiochip500 lrwxrwxrwx 1 0 0 0 Jan 3 00:40 gpiochip502 -> ../../devices/platform/10000000.sysreg/basic-mmio-gpio.1.auto/gpio/gpiochip502 lrwxrwxrwx 1 0 0 0 Jan 3 00:40 gpiochip510 -> ../../devices/platform/10000000.sysreg/gpio/gpiochip510 --w------- 1 0 0 4096 Jan 3 00:40 unexport / # echo 511 > /sys/class/gpio/unexport / # ls -al /sys/class/gpio/ total 0 drwxr-xr-x 2 0 0 0 Jan 3 00:40 . drwxr-xr-x 36 0 0 0 Jan 3 00:40 .. --w------- 1 0 0 4096 Jan 3 00:43 export lrwxrwxrwx 1 0 0 0 Jan 3 00:42 gpio510 -> ../../devices/platform/10000000.sysreg/gpiochip0/gpio/gpio510 lrwxrwxrwx 1 0 0 0 Jan 3 00:40 gpiochip499 -> ../../devices/platform/10000000.sysreg/basic-mmio-gpio.3.auto/gpio/gpiochip499 lrwxrwxrwx 1 0 0 0 Jan 3 00:40 gpiochip500 -> ../../devices/platform/10000000.sysreg/basic-mmio-gpio.2.auto/gpio/gpiochip500 lrwxrwxrwx 1 0 0 0 Jan 3 00:40 gpiochip502 -> ../../devices/platform/10000000.sysreg/basic-mmio-gpio.1.auto/gpio/gpiochip502 lrwxrwxrwx 1 0 0 0 Jan 3 00:40 gpiochip510 -> ../../devices/platform/10000000.sysreg/gpio/gpiochip510 --w------- 1 0 0 4096 Jan 3 00:43 unexport / # grep "" /sys/class/gpio/gpio510/* /sys/class/gpio/gpio510/active_low:0 /sys/class/gpio/gpio510/direction:in /sys/class/gpio/gpio510/value:0 / # echo out > /sys/class/gpio/gpio510/direction / # grep "" /sys/class/gpio/gpio510/* /sys/class/gpio/gpio510/active_low:0 /sys/class/gpio/gpio510/direction:out /sys/class/gpio/gpio510/value:0 / # cat /sys/kernel/debug/gpio gpiochip3: GPIOs 499-499, parent: platform/basic-mmio-gpio.3.auto, sys_flash: gpiochip2: GPIOs 500-501, parent: platform/basic-mmio-gpio.2.auto, sys_mci: gpio-500 ( |cd ) in lo gpio-501 ( |wp ) in lo gpiochip1: GPIOs 502-509, parent: platform/basic-mmio-gpio.1.auto, sys_led: gpio-502 ( |? ) out lo gpio-503 ( |? ) out lo gpio-504 ( |? ) out lo gpio-505 ( |? ) out lo gpio-506 ( |? ) out hi gpio-507 ( |? ) out hi gpio-508 ( |? ) out lo gpio-509 ( |? ) out lo gpiochip0: GPIOs 510-511, parent: platform/10000000.sysreg, 10000000.sysreg: gpio-510 ( |sysfs ) out lo / # grep "" /sys/class/gpio/gpiochip*/* /sys/class/gpio/gpiochip499/base:499 /sys/class/gpio/gpiochip499/label:sys_flash /sys/class/gpio/gpiochip499/ngpio:1 /sys/class/gpio/gpiochip500/base:500 /sys/class/gpio/gpiochip500/label:sys_mci /sys/class/gpio/gpiochip500/ngpio:2 /sys/class/gpio/gpiochip502/base:502 /sys/class/gpio/gpiochip502/label:sys_led /sys/class/gpio/gpiochip502/ngpio:8 /sys/class/gpio/gpiochip510/base:510 /sys/class/gpio/gpiochip510/label:10000000.sysreg /sys/class/gpio/gpiochip510/ngpio:2
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參考資料:
- https://elinux.org/GPIO
- https://elinux.org/images/c/cb/Linux_GPIO-Evolution_and_Current_State_of_the_User_API.pdf
