总线设备驱动模型---platform篇

linux从2.6起就加入了一套新的驱动管理和注册的机制platform平台总线，是一条虚拟的总线，设备用platform_device表示，驱动用platform_driver进行注册。于传统的bus/device/driver机制相比，platform由内核进行统一管理，在驱动中使用资源，提高了代码的安全性和可移植性。下面来看看内核时怎么注册platform总线的过程 点击(此处)折叠或打开
int __init platform_bus_init(void)

{

int error;

early_platform_cleanup();

error = device_register(&platform_bus);//注册了platform的设备

if (error)

return error;

error = bus_register(&platform_bus_type);//注册了platform总线

if (error)

device_unregister(&platform_bus);

return error;

}
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struct device platform_bus = {

.init_name = "platform",

};
点击(此处)折叠或打开
struct bus_type platform_bus_type = {

.name = "platform",

.dev_attrs = platform_dev_attrs,

.match = platform_match,

.uevent = platform_uevent,

.pm = &platform_dev_pm_ops,

};
其过程和总线的注册过程差不多，驱动和设备匹配后，调用platform的match函数。由传统的机制，也不难总结出platform的开发流程为1、定义一个platform_device，并注册2、定义一个platform_driver，并注册定义platform_device过程 点击(此处)折叠或打开
struct platform_device *platform_device_alloc(const char *name, int id)

{

struct platform_object *pa;

pa = kzalloc(sizeof(struct platform_object) + strlen(name), GFP_KERNEL);

if (pa) {

strcpy(pa->name, name);

pa->pdev.name = pa->name;

pa->pdev.id = id;

device_initialize(&pa->pdev.dev);

pa->pdev.dev.release = platform_device_release;

arch_setup_pdev_archdata(&pa->pdev);

}

return pa ? &pa->pdev : NULL;

}
下面首先来看看platform_device的注册过程 点击(此处)折叠或打开
struct platform_device {

const char * name; //设备名

int id; //设备ID

struct device dev;

u32 num_resources; //设备使用的资源的数目

struct resource * resource; //设备使用的资源

const struct platform_device_id *id_entry;

/* MFD cell pointer */

struct mfd_cell *mfd_cell;

/* arch specific additions */

struct pdev_archdata archdata;

};
点击(此处)折叠或打开
struct resource {

resource_size_t start;

resource_size_t end;

const char *name;

unsigned long flags;

struct resource *parent, *sibling, *child;

};
在struct resource结构中我们通常只关心start、end和flags这3个字段，分别表示资源的开始值、结束值和类型，flags可以用内存资源，IO资源，中断资源等。 点击(此处)折叠或打开
int platform_device_register(struct platform_device *pdev)

{

device_initialize(&pdev->dev);//dev初始化

arch_setup_pdev_archdata(pdev);

return platform_device_add(pdev);//加入到dev链表

}
点击(此处)折叠或打开
int platform_device_add(struct platform_device *pdev)

{

int i, ret = 0;

if (!pdev)

return -EINVAL;

if (!pdev->dev.parent)

pdev->dev.parent = &platform_bus;//父设备设置为platform_bus

pdev->dev.bus = &platform_bus_type;//设备挂载在platforrm总线上

if (pdev->id != -1)

dev_set_name(&pdev->dev, "%s.%d", pdev->name, pdev->id);

else

dev_set_name(&pdev->dev, "%s", pdev->name);

for (i = 0; i < pdev->num_resources; i++) { //完成资源的初始化

struct resource *p, *r = &pdev->resource[i];

if (r->name == NULL)

r->name = dev_name(&pdev->dev);

p = r->parent;

if (!p) {

if (resource_type(r) == IORESOURCE_MEM)

p = &iomem_resource;

else if (resource_type(r) == IORESOURCE_IO)

p = &ioport_resource;

}

if (p && insert_resource(p, r)) {

printk(KERN_ERR

"%s: failed to claim resource %d\n",

dev_name(&pdev->dev), i);

ret = -EBUSY;

goto failed;

}

}

pr_debug("Registering platform device '%s'. Parent at %s\n",

dev_name(&pdev->dev), dev_name(pdev->dev.parent));

ret = device_add(&pdev->dev);

if (ret == 0)

return ret;

failed:

while (--i >= 0) {

struct resource *r = &pdev->resource[i];

unsigned long type = resource_type(r);

if (type == IORESOURCE_MEM || type == IORESOURCE_IO)

release_resource(r);

}

return ret;

}
其上最后也是调用device_add的，其主要是将device加入到bus总线中，并由device_attach完成设备与驱动之间的匹配，这个过程在设备一篇中已经有详细的分析过程中，再看看驱动的注册过程。 点击(此处)折叠或打开
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;

};
可见，它包含了设备操作的功能函数，同时包含了device_driver结构。内核提供的platform_driver结构的注册为 点击(此处)折叠或打开
int platform_driver_register(struct platform_driver *drv)

{

drv->driver.bus = &platform_bus_type;//注册到总线上，drv与dev匹配通过platform_bus_type注册的platform_match完成

if (drv->probe)

drv->driver.probe = platform_drv_probe;

if (drv->remove)

drv->driver.remove = platform_drv_remove;

if (drv->shutdown)

drv->driver.shutdown = platform_drv_shutdown;

return driver_register(&drv->driver);

}
其注册函数中比较重要的还是调用了driver_register，添加到platform总线链表，完成设备与驱动之间的匹配过程，其主要的过程在总线设备驱动模型的驱动篇已经有过分析。 点击(此处)折叠或打开
int driver_register(struct device_driver *drv)

{

int ret;

struct device_driver *other;

BUG_ON(!drv->bus->p);

if ((drv->bus->probe && drv->probe) ||

(drv->bus->remove && drv->remove) ||

(drv->bus->shutdown && drv->shutdown))

printk(KERN_WARNING "Driver '%s' needs updating - please use "

"bus_type methods\n", drv->name);

other = driver_find(drv->name, drv->bus);

if (other) {

put_driver(other);

printk(KERN_ERR "Error: Driver '%s' is already registered, "

"aborting...\n", drv->name);

return -EBUSY;

}

ret = bus_add_driver(drv);

if (ret)

return ret;

ret = driver_add_groups(drv, drv->groups);

if (ret)

bus_remove_driver(drv);

return ret;

}
下面看看看驱动和设备的匹配过程，由以前可以看出，主要是调用bus的match函数来完成匹配。 点击(此处)折叠或打开
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);

/* Attempt an OF style match first */

if (of_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);

}
由上面可以看出，只需要比较dev的名字和drv的名字，如果是相同的话就匹配成功。在platform的设备驱动的编写有两种方法：1、在bsp版文件中实现定义，在文件中将platform_device被化为一个数组，最后通过platform_add_devices函数注册。对于2440来说位于arch\arm\mach-s3c2440\mach-smdk2440.c中定义 点击(此处)折叠或打开
static struct platform_device *smdk2440_devices[] __initdata = {

&s3c_device_usb,

&s3c_device_lcd,

&s3c_device_wdt,

&s3c_device_i2c,

&s3c_device_iis,

};
如果我们要实现一个设备的添加，那么只需要加入一个struct platform_device的数组，然后只需要编写对应的platform_driver驱动程序就可以了。从这种方法可以看出，存在一个很明显的缺点，如果要改写驱动，就要重新的编译内核。2、第二种方法只需要单独编写一个内核模块加载到内核中。例子：device文件：platform_dev.c 点击(此处)折叠或打开
struct platform_device *my_led_dev;

static int __init platform_dev_init(void)

{

int ret;

//分配一个 platform_device结构体

my_led_dev = platform_device_alloc("platform_led", -1);

ret = platform_device_add(my_led_dev);//将自定义的设备添加到内核设备架构中

if(ret)

platform_device_put(my_led_dev);//销毁platform设备结构

return ret;

}

static void __exit platform_dev_exit(void)

{

platform_device_unregister(my_led_dev);//注销platform_device

}

module_init(platform_dev_init);

module_exit(platform_dev_exit);

MODULE_AUTHOR("Sola");

MODULE_LICENSE("GPL");
drv文件：platform_drv.c
点击(此处)折叠或打开
static int s3c6410_led_open(struct inode *inode, struct file *file)

{

unsigned tmp;

tmp = readl(S3C64XX_GPMCON);

tmp = (tmp & ~(0xFFFF))|(0x1111U);

writel(tmp, S3C64XX_GPMCON);

return 0;

}

static int s3c6410_led_close(struct inode *inode, struct file *file)

{

return 0;

}

static int s3c6410_led_read(struct file *filp, char __user *buff, size_t count, loff_t *offp)

{

printk("#########read######\n");

return count;

}

static int s3c6410_led_write (struct file *filp, const char __user *buf, size_t count,loff_t *f_pos)

{

char wbuf[10];

unsigned tmp;

copy_from_user(wbuf,buf,count);

if(wbuf[0]==1)//1号灯亮

switch(wbuf[1])

{

case 0: //off

tmp = readl(S3C64XX_GPMDAT);

tmp |= (0x1U);

writel(tmp, S3C64XX_GPMDAT);

break;

case 1: //on

tmp = readl(S3C64XX_GPMDAT);

tmp &= ~(0x1U);

writel(tmp, S3C64XX_GPMDAT);

break;

default :

break;

}

if(wbuf[0]==2)//2号灯亮

switch(wbuf[1])

{

case 0: //off

tmp = readl(S3C64XX_GPMDAT);

tmp |= (0x2U);

writel(tmp, S3C64XX_GPMDAT);

break;

case 1: //on

tmp = readl(S3C64XX_GPMDAT);

tmp &= ~(0x2U);

writel(tmp, S3C64XX_GPMDAT);

break;

default :

break;

}

if(wbuf[0]==3)//3号灯亮

switch(wbuf[1])

{

case 0: //off

tmp = readl(S3C64XX_GPMDAT);

tmp |= (0x4U);

writel(tmp, S3C64XX_GPMDAT);

break;

case 1: //on

tmp = readl(S3C64XX_GPMDAT);

tmp &= ~(0x4U);

writel(tmp, S3C64XX_GPMDAT);

break;

default :

break;

}

if(wbuf[0]==4)//4号灯亮

switch(wbuf[1])

{

case 0: //off

tmp = readl(S3C64XX_GPMDAT);

tmp |= (0x8U);

writel(tmp, S3C64XX_GPMDAT);

break;

case 1: //on

tmp = readl(S3C64XX_GPMDAT);

tmp &= ~(0x8U);

writel(tmp, S3C64XX_GPMDAT);

break;

default :

break;

}

return count;

}

static struct file_operations led_fops = {

.owner = THIS_MODULE,

.open = s3c6410_led_open,

.release = s3c6410_led_close,

.read = s3c6410_led_read,

.write = s3c6410_led_write,

};

static int my_plat_probe(struct platform_device *dev)

{

int rc;

printk("Test platform_led dev\n");

//注册设备

rc = register_chrdev(LED_MAJOR,"platform_led",&led_fops);

if (rc <0)

{

printk ("register %s char dev error\n","led");

return -1;

}

printk ("ok!\n");

return 0;

}

static int my_plat_remove(struct platform_device *dev)

{

printk("my platfrom device has removed.\n");

return 0;

}

struct platform_driver my_led_drv = {

.probe = my_plat_probe,

.remove = my_plat_remove,

.driver = {

.owner = THIS_MODULE,

.name = "platform_led",

},

};

static int __init platform_drv_init(void)

{

int ret;

ret = platform_driver_register(&my_led_drv);

return ret;

}

static void __exit platform_drv_exit(void)

{

platform_driver_unregister(&my_led_drv);

}

module_init(platform_drv_init);

module_exit(platform_drv_exit);

MODULE_LICENSE("GPL");

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