設備樹

下面截取gpio0的設備樹，復制自：linux_5.10/arch/riscv/boot/dts/cvitek/cv180x_base.dtsi

gpio0: gpio@03020000 {
	compatible = "snps,dw-apb-gpio";
	reg = ;
	#address-cells = ;
	#size-cells = ;

	porta: gpio-controller@0 {
		compatible = "snps,dw-apb-gpio-port";
		bank-name = "porta";
		gpio-controller;
		#gpio-cells = ;
		snps,nr-gpios = ;
		reg = ;
	};
};

以下是復制自：linux_5.10/arch/riscv/boot/dts/cvitek/cv180x_base_riscv.dtsi

gpio0: gpio@03020000 {
		porta: gpio-controller@0 {
			interrupt-controller;
			interrupts = ;
			interrupt-parent = ;
		};
	};

驅動

cv180x的GPIO控制器用到是dw-apb-gpio控制器驅動，驅動代碼位于：linux_5.10/drivers/gpio/gpio-dwapb.c

#define DWAPB_DRIVER_NAME	"gpio-dwapb"

// 省略其他代碼

static struct platform_driver dwapb_gpio_driver = {
	.driver		= {
		.name	= DWAPB_DRIVER_NAME,
		.pm	= &dwapb_gpio_pm_ops,
		.of_match_table = dwapb_of_match,
		.acpi_match_table = dwapb_acpi_match,
	},
	.probe		= dwapb_gpio_probe,
};

module_platform_driver(dwapb_gpio_driver);

關鍵函數是probe函數

// drivers/gpio/gpio-dwapb.c
dwapb_gpio_probe:

	dwapb_gpio_get_pdata(dev)

		device_for_each_child_node(dev, fwnode)  { //遍歷設備樹節點

			fwnode_property_read_u32(fwnode, "snps,nr-gpios", &pp->ngpio)

			fwnode_property_read_u32(fwnode, "reg", &pp->idx)

		}

		dwapb_gpio_add_port

			devm_gpiochip_add_data

				devm_gpiochip_add_data_with_key

					gpiochip_add_data_with_key //注冊到gpiolib的gpio_devices中

gpio子系統

// drivers/gpio/gpiolib.c
struct gpio_desc *gpio_to_desc(unsigned gpio) //從gpio_devices獲取gpio_desc

// include/asm-generic/gpio.h
// drivers/gpio/gpiolib-sysfs.c
gpio_export:
	gpiod_export(gpio_to_desc(gpio), direction_may_change)
		device_create_with_groups
			device_create_groups_vargs
				device_add
					kobject_add //添加到相關的設備模型子系統
					device_create_file //創建/sys下的設備屬性文件
					... //其他相關設置

小結

通過上面的3塊，就實現了/sys/class/gpio/export導出gpio的過程即對gpio的操作。

關于gpio的相關操作函數就在gpiolib.c里面。

審核編輯 黃宇