jz2440_LED_设备树之点亮LED灯

简介：设备驱动程序中，总线驱动模型和设备树的差别在于平台设备的构建不同，在传统平台设备驱动程序写在C文件中，使用设备树时，平台设备之前不存在，在dts文件中构造节点，节点里面含有资源，设备树详细的内容我会在以后的博客中详细介绍。

CPU : jz2440
u-boot: u-boot-1.1.6
kernel: linux-4.19-rc3
root ：fs_mini_mdev_new

/* platform_device结构体定义 */
struct platform_device {
	const char	*name;
	int		id;
	bool		id_auto;
	struct device	dev;
	u32		num_resources;
	struct resource	*resource;

	const struct platform_device_id	*id_entry;
	char *driver_override; /* Driver name to force a match */

	/* MFD cell pointer */
	struct mfd_cell *mfd_cell;

	/* arch specific additions */
	struct pdev_archdata	archdata;
};

/* platform_device示例 */
struct platform_driver led_drv = {
	.probe		= led_probe,
	.remove		= led_remove,
	.driver		= {
		.name	= "myled",
	}
};

/* platform_driver结构体定义 */
struct platform_driver {
	int (*probe)(struct platform_device *);
	int (*remove)(struct platform_device *);
	void (*shutdown)(struct platform_device *);
	int (*suspend)(struct platform_device *, pm_message_t state);
	int (*resume)(struct platform_device *);
	struct device_driver driver;
	const struct platform_device_id *id_table;
	bool prevent_deferred_probe;
};

/* platform_driver结构体示例 */
struct platform_driver led_drv = {
	.probe		= led_probe,
	.remove		= led_remove,
	.driver		= {
		.name	= "myled",
	}
};

由于本文档的目的是简单介绍传统的总线驱动模型和设备树的区别，总线驱动模型的详细就不再介绍，详细介绍可以参考linux设备驱动模型之总线、设备、驱动三者的关系

下面简单分析设备树的匹配

static int platform_match(struct device *dev, struct device_driver *drv)
{
	struct platform_device *pdev = to_platform_device(dev);
	struct platform_driver *pdrv = to_platform_driver(drv);

	/* When driver_override is set, only bind to the matching driver */
	if (pdev->driver_override)
		return !strcmp(pdev->driver_override, drv->name);

	/* Attempt an OF style match first */
	if (of_driver_match_device(dev, drv))  //用于判断从设备树得到的platform_device与platform_driver是否匹配
		return 1;

	/* Then try ACPI style match */
	if (acpi_driver_match_device(dev, drv))
		return 1;

	/* Then try to match against the id table */
	if (pdrv->id_table)
		return platform_match_id(pdrv->id_table, pdev) != NULL;

	/* fall-back to driver name match */
	return (strcmp(pdev->name, drv->name) == 0);
}

static inline int of_driver_match_device(struct device *dev,
					 const struct device_driver *drv)
{
	return of_match_device(drv->of_match_table, dev) != NULL;
}

static inline int of_driver_match_device(struct device *dev,
					 const struct device_driver *drv)
{
	return of_match_device(drv->of_match_table, dev) != NULL;
}

根据上面的函数可以看出，从设备树得到的platform_device中的节点和platform_driver中的of_device_id是否匹配，匹配成功之后，就会调用platform_driver中的probe函数。

设备树文件

/dts-v1/;

/ {
	model = "SMDK24440";
	compatible = "samsung,smdk2440";

	#address-cells = <1>;
	#size-cells = <1>;
		
	memory@30000000 {
		device_type = "memory";
		reg =  <0x30000000 0x4000000>;
	};
/*
	cpus {
		cpu {
			compatible = "arm,arm926ej-s";
		};
	};
*/	
	chosen {
		bootargs = "noinitrd root=/dev/mtdblock4 rw init=/linuxrc console=ttySAC0,115200";
	};

	
	led {
		compatible = "jz2440_led";  
		pin = ;
	};
};

平台驱动文件

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 


static int led_pin;
static volatile unsigned int *gpio_con;
static volatile unsigned int *gpio_dat;

/* 123. 分配/设置/注册file_operations 
 * 4. 入口
 * 5. 出口
 */

static int major;
static struct class *led_class;

static unsigned int gpio_base[] = {
	0x56000000, /* GPACON */
	0x56000010, /* GPBCON */
	0x56000020, /* GPCCON */
	0x56000030, /* GPDCON */
	0x56000040, /* GPECON */
	0x56000050, /* GPFCON */
	0x56000060, /* GPGCON */
	0x56000070, /* GPHCON */
	0,          /* GPICON */
	0x560000D0, /* GPJCON */
};

static int led_open (struct inode *node, struct file *filp)
{
	/* 把LED引脚配置为输出引脚 */
	/* GPF5 - 0x56000050 */
	int bank = led_pin >> 16;
	int base = gpio_base[bank];

	int pin = led_pin & 0xffff;
	gpio_con = ioremap(base, 8);
	if (gpio_con) {
		printk("ioremap(0x%x) = 0x%x\n", base, gpio_con);
	}
	else {
		return -EINVAL;
	}
	
	gpio_dat = gpio_con + 1;
	
	*gpio_con &= ~(3<<(pin * 2));
	*gpio_con |= (1<<(pin * 2));  

	return 0;
}

static ssize_t led_write (struct file *filp, const char __user *buf, size_t size, loff_t *off)
{
	/* 根据APP传入的值来设置LED引脚 */
	unsigned char val;
	int pin = led_pin & 0xffff;
	
	copy_from_user(&val, buf, 1);

	if (val)
	{
		/* 点灯 */
		*gpio_dat &= ~(1<start;
	}
	else {
		/* 获得pin属性 */
		of_property_read_s32(pdev->dev.of_node, "pin", &led_pin);
	}

	if (!led_pin) 
	{
		printk("can not get pin for led\n");
		return -EINVAL;
	}
	
	major = register_chrdev(0, "myled", &myled_oprs);

	led_class = class_create(THIS_MODULE, "myled");
	device_create(led_class, NULL, MKDEV(major, 0), NULL, "led"); /* /dev/led */
	
	return 0;
}

static int led_remove(struct platform_device *pdev)
{
	unregister_chrdev(major, "myled");
	device_destroy(led_class,  MKDEV(major, 0));
	class_destroy(led_class);
	
	return 0;
}


static const struct of_device_id of_match_leds[] = {
	{ .compatible = "jz2440_led", .data = NULL },
	{ /* Sentinel */ }
};


struct platform_driver led_drv = {
	.probe		= led_probe,
	.remove		= led_remove,
	.driver		= {
		.name	= "myled",
		.of_match_table	= of_match_leds, //能支持哪些来自于dts的platform_device
	}
};

static int myled_init(void)
{
	platform_driver_register(&led_drv);
	return 0;
}

static void myled_exit(void)
{
	platform_driver_unregister(&led_drv);
}

module_init(myled_init);
module_exit(myled_exit);

MODULE_LICENSE("GPL");