0、说明

        GPIO完成对CPU支持GPIO的访问，如拉高，拉低等。本文分析linux下gpio子系统。

1、环境

1.1 硬件环境

• Xilinx ZYNQ开发板

1.2 软件环境

• VM ubuntu 18.04
• windows 10

2、GPIO子系统数据结构

2.1 代码路径

drivers/gpio/gpiolib.c
drivers/gpio/gpio-zynq.c

2.2 关键结构体

gpio_device

        一个GPIO控制器对应一个gpio_device。

struct gpio_device {                                                         
    int         id;                                                          
    struct device       dev;                                                 
    struct cdev     chrdev;                                                  
    struct device       *mockdev;                                            
    struct module       *owner;                                              
    struct gpio_chip    *chip;                                               
    struct gpio_desc    *descs; //数组，支持的所有gpio描述信息                                              
    int         base;  //编号基数                                                      
    u16         ngpio; //支持多少个GPIO                                                      
    const char      *label;                                                  
    void            *data;                                                   
    struct list_head        list;                                            
    struct blocking_notifier_head notifier;                                  
                                                                             
#ifdef CONFIG_PINCTRL                                                        
    /*                                                                       
     * If CONFIG_PINCTRL is enabled, then gpio controllers can optionally    
     * describe the actual pin range which they serve in an SoC. This        
     * information would be used by pinctrl subsystem to configure           
     * corresponding pins for gpio usage.                                    
     */                                                                      
    struct list_head pin_ranges;                                             
#endif                                                                       
};

gpio_desc 

        一个gpio对应一个gpio_desc，在使用gpiod_get时返回该GPIO对应的gpio_desc，gpio_desc中存有gpio_device信息，可以找到所属控制器。

struct gpio_desc {                                                                                                   
    struct gpio_device  *gdev;                                                                                       
    unsigned long       flags;                                                                                       
/* flag symbols are bit numbers */                                                                                   
#define FLAG_REQUESTED  0                                                                                            
#define FLAG_IS_OUT 1                                                                                                
#define FLAG_EXPORT 2   /* protected by sysfs_lock */                                                                
#define FLAG_SYSFS  3   /* exported via /sys/class/gpio/control */                                                   
#define FLAG_ACTIVE_LOW 6   /* value has active low */                                                               
#define FLAG_OPEN_DRAIN 7   /* Gpio is open drain type */                                                            
#define FLAG_OPEN_SOURCE 8  /* Gpio is open source type */                                                           
#define FLAG_USED_AS_IRQ 9  /* GPIO is connected to an IRQ */                                                        
#define FLAG_IRQ_IS_ENABLED 10  /* GPIO is connected to an enabled IRQ */                                            
#define FLAG_IS_HOGGED  11  /* GPIO is hogged */                                                                     
#define FLAG_TRANSITORY 12  /* GPIO may lose value in sleep or reset */                                              
#define FLAG_PULL_UP    13  /* GPIO has pull up enabled */                                                           
#define FLAG_PULL_DOWN  14  /* GPIO has pull down enabled */                                                         
#define FLAG_BIAS_DISABLE    15 /* GPIO has pull disabled */                                                         
#define FLAG_EDGE_RISING     16 /* GPIO CDEV detects rising edge events */                                           
#define FLAG_EDGE_FALLING    17 /* GPIO CDEV detects falling edge events */                                          
                                                                                                                     
    /* Connection label */                                                                                           
    const char      *label;                                                                                          
    /* Name of the GPIO */                                                                                           
    const char      *name;                                                                                           
#ifdef CONFIG_OF_DYNAMIC                                                                                             
    struct device_node  *hog;                                                                                        
#endif                                                                                                               
#ifdef CONFIG_GPIO_CDEV                                                                                              
    /* debounce period in microseconds */                                                                            
    unsigned int        debounce_period_us;                                                                          
#endif                                                                                                               
}; 

gpio_chip 

        GPIO控制器驱动中创建gpio_chip，通过gpiochip_add_data向系统注册gpio_device来描述一个GPIO控制器。

struct gpio_chip {
	const char		*label;
	struct gpio_device	*gpiodev;
	struct device		*parent;
	struct module		*owner;

	int			(*request)(struct gpio_chip *gc,
						unsigned int offset);
	void			(*free)(struct gpio_chip *gc,
						unsigned int offset);
	int			(*get_direction)(struct gpio_chip *gc,
						unsigned int offset);
	int			(*direction_input)(struct gpio_chip *gc,
						unsigned int offset);
	int			(*direction_output)(struct gpio_chip *gc,
						unsigned int offset, int value);
	int			(*get)(struct gpio_chip *gc,
						unsigned int offset);
	int			(*get_multiple)(struct gpio_chip *gc,
						unsigned long *mask,
						unsigned long *bits);
	void			(*set)(struct gpio_chip *gc,
						unsigned int offset, int value);
	void			(*set_multiple)(struct gpio_chip *gc,
						unsigned long *mask,
						unsigned long *bits);
	int			(*set_config)(struct gpio_chip *gc,
					      unsigned int offset,
					      unsigned long config);
	int			(*to_irq)(struct gpio_chip *gc,
						unsigned int offset);

	void			(*dbg_show)(struct seq_file *s,
						struct gpio_chip *gc);

	int			(*init_valid_mask)(struct gpio_chip *gc,
						   unsigned long *valid_mask,
						   unsigned int ngpios);

	int			(*add_pin_ranges)(struct gpio_chip *gc);

	int			base;
	u16			ngpio;
	const char		*const *names;
	bool			can_sleep;

#if IS_ENABLED(CONFIG_GPIO_GENERIC)
	unsigned long (*read_reg)(void __iomem *reg);
	void (*write_reg)(void __iomem *reg, unsigned long data);
	bool be_bits;
	void __iomem *reg_dat;
	void __iomem *reg_set;
	void __iomem *reg_clr;
	void __iomem *reg_dir_out;
	void __iomem *reg_dir_in;
	bool bgpio_dir_unreadable;
	int bgpio_bits;
	spinlock_t bgpio_lock;
	unsigned long bgpio_data;
	unsigned long bgpio_dir;
#endif /* CONFIG_GPIO_GENERIC */

#ifdef CONFIG_GPIOLIB_IRQCHIP
	/*
	 * With CONFIG_GPIOLIB_IRQCHIP we get an irqchip inside the gpiolib
	 * to handle IRQs for most practical cases.
	 */

	/**
	 * @irq:
	 *
	 * Integrates interrupt chip functionality with the GPIO chip. Can be
	 * used to handle IRQs for most practical cases.
	 */
	struct gpio_irq_chip irq;
#endif /* CONFIG_GPIOLIB_IRQCHIP */

	/**
	 * @valid_mask:
	 *
	 * If not %NULL holds bitmask of GPIOs which are valid to be used
	 * from the chip.
	 */
	unsigned long *valid_mask;

#if defined(CONFIG_OF_GPIO)
	/*
	 * If CONFIG_OF is enabled, then all GPIO controllers described in the
	 * device tree automatically may have an OF translation
	 */

	/**
	 * @of_node:
	 *
	 * Pointer to a device tree node representing this GPIO controller.
	 */
	struct device_node *of_node;

	/**
	 * @of_gpio_n_cells:
	 *
	 * Number of cells used to form the GPIO specifier.
	 */
	unsigned int of_gpio_n_cells;

	/**
	 * @of_xlate:
	 *
	 * Callback to translate a device tree GPIO specifier into a chip-
	 * relative GPIO number and flags.
	 */
	int (*of_xlate)(struct gpio_chip *gc,
			const struct of_phandle_args *gpiospec, u32 *flags);
#endif /* CONFIG_OF_GPIO */
};

of_phandle_args

2.3 关键API

gpiod_get

led_gpio = gpiod_get(&pdev->dev, "led", 0);

struct gpio_desc *__must_check gpiod_get(struct device *dev, const char *con_id, enum gpiod_flags flags)
	gpiod_get_index(dev, "led", 0, 0);
		desc = of_find_gpio(dev, "led", 0, &lookupflags);
			of_get_named_gpiod_flags(dev->of_node, led-gpios, 0, &of_flags);
				of_parse_phandle_with_args_map(np, led-gpios, "gpio", 0, &gpiospec);
					__of_parse_phandle_with_args(np, led-gpios, gpio-cells, -1, 0, out_args);
				chip = of_find_gpiochip_by_xlate(&gpiospec);
				desc = of_xlate_and_get_gpiod_flags(chip, &gpiospec, flags);

gpio_request

gpiod_set_value

gpiod_set_value(led_gpio_desc, 0);
gpiod_set_value(struct gpio_desc *desc, int value)
	 gpiod_set_value_nocheck(desc, value);
		if (test_bit(FLAG_ACTIVE_LOW, &desc->flags))
			value = !value;
		gpiod_set_raw_value_commit(desc, value);
			gc = desc->gdev->chip;

3、GPIO子系统

3.1 设备树中的描述

        gpio0: gpio@e000a000 {
            compatible = "xlnx,zynq-gpio-1.0";
            #gpio-cells = <2>;
            clocks = <&clkc 42>;
            gpio-controller;
            interrupt-controller;
            #interrupt-cells = <2>;
            interrupt-parent = <&intc>;
            interrupts = <0 20 4>;
            reg = <0xe000a000 0x1000>;
        };

3.2 GPIO控制器驱动

3.2.1 GPIO控制器驱动主要任务

        如下分析，gpio控制器驱动中主要完成：

• 匹配设备树与驱动中的私有数据
• 获取设备树中的io资源与中断资源
• 初始化配置gpio_chip中的函数
• 设置gpio_chip中的irq资源
• gpiochip_add_data完成gpio注册到内核中

/**
 * zynq_gpio_probe - Initialization method for a zynq_gpio device
 * @pdev:	platform device instance
 *
 * This function allocates memory resources for the gpio device and registers
 * all the banks of the device. It will also set up interrupts for the gpio
 * pins.
 * Note: Interrupts are disabled for all the banks during initialization.
 *
 * Return: 0 on success, negative error otherwise.
 */
static int zynq_gpio_probe(struct platform_device *pdev)
{
	int ret, bank_num;
	struct zynq_gpio *gpio;
	struct gpio_chip *chip;
	struct gpio_irq_chip *girq;
	const struct of_device_id *match;

    //分配zynq_gpio，同时分配了gpio_chip
	gpio = devm_kzalloc(&pdev->dev, sizeof(*gpio), GFP_KERNEL);
	if (!gpio)
		return -ENOMEM;

    //通过设备树中的配置匹配zynq_gpio_of_match并获取对应的私有数据
	match = of_match_node(zynq_gpio_of_match, pdev->dev.of_node);
	if (!match) {
		dev_err(&pdev->dev, "of_match_node() failedn");
		return -EINVAL;
	}
	gpio->p_data = match->data;
	platform_set_drvdata(pdev, gpio);

    //从设备树获取IORESOURCE_MEM资源，即reg属性中的GPIO寄存器基址
	gpio->base_addr = devm_platform_ioremap_resource(pdev, 0);
	if (IS_ERR(gpio->base_addr))
		return PTR_ERR(gpio->base_addr);

    //从设备树获取GPIO IRQ资源，记录硬件中断号
	gpio->irq = platform_get_irq(pdev, 0);
	if (gpio->irq < 0)
		return gpio->irq;

    //设置gpio_chip的操作函数等，在get/set/request等时调用到chip中函数
	/* configure the gpio chip */
	chip = &gpio->chip;
	chip->label = gpio->p_data->label; //label = "zynq_gpio"
	chip->owner = THIS_MODULE;
	chip->parent = &pdev->dev;
	chip->get = zynq_gpio_get_value;
	chip->set = zynq_gpio_set_value;
	chip->request = zynq_gpio_request;
	chip->free = zynq_gpio_free;
	chip->direction_input = zynq_gpio_dir_in;
	chip->direction_output = zynq_gpio_dir_out;
	chip->get_direction = zynq_gpio_get_direction;
    //设置gpio_chip的编号基址
	chip->base = of_alias_get_id(pdev->dev.of_node, "gpio");
    //支持的个数  118个
	chip->ngpio = gpio->p_data->ngpio;

	/* Retrieve GPIO clock */
	gpio->clk = devm_clk_get(&pdev->dev, NULL);
	if (IS_ERR(gpio->clk))
		return dev_err_probe(&pdev->dev, PTR_ERR(gpio->clk), "input clock not found.n");

	ret = clk_prepare_enable(gpio->clk);
	if (ret) {
		dev_err(&pdev->dev, "Unable to enable clock.n");
		return ret;
	}

	spin_lock_init(&gpio->dirlock);

	pm_runtime_set_active(&pdev->dev);
	pm_runtime_enable(&pdev->dev);
	ret = pm_runtime_resume_and_get(&pdev->dev);
	if (ret < 0)
		goto err_pm_dis;

	/* disable interrupts for all banks */
	for (bank_num = 0; bank_num < gpio->p_data->max_bank; bank_num++) {
		writel_relaxed(ZYNQ_GPIO_IXR_DISABLE_ALL, gpio->base_addr +
			       ZYNQ_GPIO_INTDIS_OFFSET(bank_num));
		if (gpio->p_data->quirks & GPIO_QUIRK_VERSAL)
			bank_num = bank_num + VERSAL_UNUSED_BANKS;
	}

    //设置中断资源，在中断子系统中，需要gpio子系统提供中断handle函数
	/* Set up the GPIO irqchip */
	girq = &chip->irq;
	girq->chip = &zynq_gpio_edge_irqchip; //提供irq_chip相关中断预处理函数
	girq->parent_handler = zynq_gpio_irqhandler;//父级handle
	girq->num_parents = 1;
	girq->parents = devm_kcalloc(&pdev->dev, 1,
				     sizeof(*girq->parents),
				     GFP_KERNEL);
	if (!girq->parents) {
		ret = -ENOMEM;
		goto err_pm_put;
	}
	girq->parents[0] = gpio->irq;
	girq->default_type = IRQ_TYPE_NONE;
	girq->handler = handle_level_irq;

    //注册gpio_chip，将在core层产生gpio_device
   	ret = gpiochip_add_data(chip, gpio);
	if (ret) {
		dev_err(&pdev->dev, "Failed to add gpio chipn");
		goto err_pm_put;
	}

	irq_set_status_flags(gpio->irq, IRQ_DISABLE_UNLAZY);
	device_init_wakeup(&pdev->dev, 1);
	pm_runtime_put(&pdev->dev);

	return 0;

err_pm_put:
	pm_runtime_put(&pdev->dev);
err_pm_dis:
	pm_runtime_disable(&pdev->dev);
	clk_disable_unprepare(gpio->clk);

	return ret;
}

3.2.2 gpiochip_add_data函数分析

总结

结构体关系

        一个GPIO控制器，对应一个gpio_chip结构体在驱动中实现其内部函数的配置，最终通过gpiochip_add_data注册进内核，内核同时生成gpio_device结构体。所有gpio_device被放置在gpio_devices全局链表中。

最后

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