of_get_named_gpio()函数解析

why to do

今天做试验，发现节点中的信息读不到，就想看一下，这函数是否递归搜索。
这个函数

	/* 提取GPIO */
	for (i = 0; i < KEY_NUM; i++) {
		imx6uirq.irqkeydesc[i].gpio = of_get_named_gpio(imx6uirq.nd ,"key-gpio", i);
		if (imx6uirq.irqkeydesc[i].gpio < 0) {
			printk("can't get key%d\r\n", i);
		}
	}

正确写法

interrupt_keys: interrupt_keys{
	#address-cells = <1>;
	#size-cells = <1>;
	compatible = "atkalpha-key";
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_gpio_keys>;
	key-gpio = <&gpio1 18 GPIO_ACTIVE_LOW>; /* KEY0 */
	interrupt-parent = <&gpio1>;
	interrupts = <18 IRQ_TYPE_EDGE_BOTH>; /* FALLING RISING */
	status = "okay";
	
};

写成这样就读不到gpio了

interrupt_keys: interrupt_keys@0{
	#address-cells = <1>;
	#size-cells = <1>;
	compatible = "atkalpha-key";
	pinctrl-names = "default";
	key0@0{
		pinctrl-0 = <&pinctrl_gpio_keys>;
		compatible = "atkalpha-key";
		pinctrl-names = "default";
		key-gpio = <&gpio1 18 GPIO_ACTIVE_LOW>; /* KEY0 */
		interrupt-parent = <&gpio1>;
		interrupts = <18 IRQ_TYPE_EDGE_BOTH>; /* FALLING RISING */
		status = "okay";
	};
	
};

代码解析

该函数返回一个gpio编号。

/**
 * of_get_named_gpio() - Get a GPIO number to use with GPIO API
 * @np:		device node to get GPIO from
 * @propname:	Name of property containing gpio specifier(s)
 * @index:	index of the GPIO
 *
 * Returns GPIO number to use with Linux generic GPIO API, or one of the errno
 * value on the error condition.
 */
static inline int of_get_named_gpio(struct device_node *np,
                                   const char *propname, int index)
{
	return of_get_named_gpio_flags(np, propname, index, NULL);
}

继续调用of_get_named_gpiod_flags，返回一个struct gpio_desc

//drivers/gpio/gpiolib-of.c

int of_get_named_gpio_flags(struct device_node *np, const char *list_name,
			    int index, enum of_gpio_flags *flags)
{
	struct gpio_desc *desc;

	desc = of_get_named_gpiod_flags(np, list_name, index, flags);

	if (IS_ERR(desc))
		return PTR_ERR(desc);
	else
		return desc_to_gpio(desc);
}

继续调用of_get_named_gpiod_flags

/**
 * of_get_named_gpiod_flags() - Get a GPIO descriptor and flags for GPIO API
 * @np:		device node to get GPIO from
 * @propname:	property name containing gpio specifier(s)
 * @index:	index of the GPIO
 * @flags:	a flags pointer to fill in
 *
 * Returns GPIO descriptor to use with Linux GPIO API, or one of the errno
 * value on the error condition. If @flags is not NULL the function also fills
 * in flags for the GPIO.
 */
struct gpio_desc *of_get_named_gpiod_flags(struct device_node *np,
		     const char *propname, int index, enum of_gpio_flags *flags)
{
	/* Return -EPROBE_DEFER to support probe() functions to be called
	 * later when the GPIO actually becomes available
	 */
	struct gg_data gg_data = {
		.flags = flags,
		.out_gpio = ERR_PTR(-EPROBE_DEFER)
	};
	int ret;

	/* .of_xlate might decide to not fill in the flags, so clear it. */
	if (flags)
		*flags = 0;

//以上都是设置返回值的default


	ret = of_parse_phandle_with_args(np, propname, "#gpio-cells", index,
					 &gg_data.gpiospec);
	if (ret) {
		pr_debug("%s: can't parse '%s' property of node '%s[%d]'\n",
			__func__, propname, np->full_name, index);
		return ERR_PTR(ret);
	}

	gpiochip_find(&gg_data, of_gpiochip_find_and_xlate);

	of_node_put(gg_data.gpiospec.np);
	pr_debug("%s: parsed '%s' property of node '%s[%d]' - status (%d)\n",
		 __func__, propname, np->full_name, index,
		 PTR_ERR_OR_ZERO(gg_data.out_gpio));
	return gg_data.out_gpio;
}

of_parse_phandle_with_args：本例中，propname = “key-gpio”，idx= 0。引用的文章讲解的很清晰了，这里不再展开。

/**
 * of_parse_phandle_with_args() - Find a node pointed by phandle in a list
 * @np:		pointer to a device tree node containing a list
 * @list_name:	property name that contains a list
 * @cells_name:	property name that specifies phandles' arguments count
 * @index:	index of a phandle to parse out
 * @out_args:	optional pointer to output arguments structure (will be filled)
 *
 * This function is useful to parse lists of phandles and their arguments.
 * Returns 0 on success and fills out_args, on error returns appropriate
 * errno value.
 *
 * Caller is responsible to call of_node_put() on the returned out_args->np
 * pointer.
 *
 * Example:
 *
 * phandle1: node1 {
 *	#list-cells = <2>;
 * }
 *
 * phandle2: node2 {
 *	#list-cells = <1>;
 * }
 *
 * node3 {
 *	list = <&phandle1 1 2 &phandle2 3>;
 * }
 *
 * To get a device_node of the `node2' node you may call this:
 * of_parse_phandle_with_args(node3, "list", "#list-cells", 1, &args);
 */
int of_parse_phandle_with_args(const struct device_node *np, const char *list_name,
				const char *cells_name, int index,
				struct of_phandle_args *out_args)
{
	if (index < 0)
		return -EINVAL;
	return __of_parse_phandle_with_args(np, list_name, cells_name, 0,
					    index, out_args);
}

根据注释例子：list节点下的信息形成一个表，第一个元素中，#list-cells表示其后面跟着多少个元素是一个整体。

of_parse_phandle_with_args函数中，gpio1的cells长度为2，即后面跟的两个一起是一个整体

gpio1: gpio@0209c000 {
	compatible = "fsl,imx6ul-gpio", "fsl,imx35-gpio";
	reg = <0x0209c000 0x4000>;
	interrupts = <GIC_SPI 66 IRQ_TYPE_LEVEL_HIGH>,
		     <GIC_SPI 67 IRQ_TYPE_LEVEL_HIGH>;
	gpio-controller;
	#gpio-cells = <2>;
	interrupt-controller;
	#interrupt-cells = <2>;
};