ath79_gpio_read
polarity = ~ath79_gpio_read(ctrl, AR71XX_GPIO_REG_IN);
pending = ath79_gpio_read(ctrl, AR71XX_GPIO_REG_INT_PENDING);
state = ath79_gpio_read(ctrl, AR71XX_GPIO_REG_IN);
old_val = ath79_gpio_read(ctrl, reg);