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GPIO Development and Testing

Pin identification and GPIO numbering​

Do not copy a global GPIO number from another SoC. Confirm the controller and bank in the final Device Tree first, then use the descriptor-based GPIO API. When an old sysfs workflow requires a global number, derive it from the controller base and bank offset. Prefer libgpiod for new designs.

cat /sys/kernel/debug/gpio
cat /sys/kernel/debug/pinctrl/*/pinmux-pins
cat /sys/kernel/debug/pinctrl/*/pinconf-pins

Using GPIO in a driver​

Prefer the descriptor API:

struct gpio_desc *enable;

enable = devm_gpiod_get(dev, "enable", GPIOD_OUT_LOW);
if (IS_ERR(enable))
        return PTR_ERR(enable);

gpiod_set_value_cansleep(enable, 1);

The Device Tree property enable-gpios maps to the consumer name "enable". Convert a GPIO to an IRQ with gpiod_to_irq() and request it with devm_request_threaded_irq().

Userspace validation​

Use libgpiod on recent root filesystems:

gpioinfo
gpioget gpiochip0 14
gpioset gpiochip0 14=1

For an older BSP that still exposes sysfs:

echo <GPIO_NUM> > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio<GPIO_NUM>/direction
echo 1 > /sys/class/gpio/gpio<GPIO_NUM>/value

Rebuild the kernel, decompile the DTB, and confirm that the intended pinctrl state is present in the final image.

Common build and flash workflow​

cd <ANDROID_TOP>/longan
./build.sh kernel
./build.sh pack

After flashing, confirm the kernel/DTB build timestamp and version so that new changes are not evaluated on an old image.