Linux驱动修炼之道-platform

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努力成为linux kernel hacker的人李万鹏原创作品，为梦而战。转载请标明出处

http://blog.csdn.net/woshixingaaa/archive/2011/05/21/6436172.aspx

首先看一下我的系统中都有什么设备挂在了platform虚拟总线上：

platform的初始化：首先系统启动的时候会调用platform_bus_init来初始化这个虚拟总线，让后向虚拟总线注册即将挂载这条总线上的设备。platform_bus_type部分是内核为我们实现好的，我们只关系platform_device与platform_driver就行了。

struct bus_type platform_bus_type = { .name = "platform", .dev_attrs = platform_dev_attrs, .match = platform_match, .uevent = platform_uevent, .pm = PLATFORM_PM_OPS_PTR, }; EXPORT_SYMBOL_GPL(platform_bus_type); int __init platform_bus_init(void) { int error; early_platform_cleanup(); error = device_register(&platform_bus); if (error) return error; error = bus_register(&platform_bus_type); if (error) device_unregister(&platform_bus); return error; }

记住总线也是一种设备，所以首先注册总线设备，然后注册总线。

static struct platform_device *smdk2410_devices[] __initdata = { &s3c_device_usb, &s3c_device_lcd, &s3c_device_wdt, &s3c_device_i2c0, &s3c_device_iis, };

把设备挂到platform总线上：

static void __init smdk2410_init(void) { s3c_i2c0_set_platdata(NULL); platform_add_devices(smdk2410_devices, ARRAY_SIZE(smdk2410_devices)); smdk_machine_init(); }

首先来看一个重要的数据结构：

struct resource { resource_size_t start; /*资源的起始物理地址*/ resource_size_t end; /*资源的结束物理地址*/ const char *name; /*资源的名称*/ unsigned long flags; /*资源的类型*/ struct resource *parent, *sibling, *child; /*资源的链表指针*/ }; struct platform_device { const char * name; /*设备名*/ int id; /*设备编号，配合设备名使用*/ struct device dev; u32 num_resources; struct resource * resource; /*设备资源*/ struct platform_device_id *id_entry; }; 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 (*suspend_late)(struct platform_device *, pm_message_t state); int (*resume_early)(struct platform_device *); int (*resume)(struct platform_device *); struct device_driver driver; struct platform_device_id *id_table; };

设备的分配：

struct platform_device *platform_device_alloc(const char *name, int id); //name:设备名，id:设备id，一般为-1

设备的注册：

int platform_device_add(struct platform_device *pdev)；

获取资源:

struct resource *platform_get_resource(struct platform_device *dev, unsigned int type, unsigned int num);

/*dev:资源所属的设备，type:获取的资源类型，num:获取的资源数*/
这里详述platform_device与platform_driver是怎样匹配上的，这里跟踪函数的执行过程，首先是platform_driver_register：

int platform_driver_register(struct platform_driver *drv) { 。。。。。。。。。。 return driver_register(&drv->driver); } int driver_register(struct device_driver *drv) { 。。。。。。。。。。。 ret = bus_add_driver(drv); 。。。。。。。。。。。 } int bus_add_driver(struct device_driver *drv) { 。。。。。。。。。。。。 if (drv->bus->p->drivers_autoprobe) { error = driver_attach(drv); if (error) goto out_unregister; } 。。。。。。。。。。。。 } int driver_attach(struct device_driver *drv) { return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach); }

这里来看__driver_attach这个函数，其中分别调用了driver_match_device，driver_probe_device函数。如果匹配成果调用probe函数，否则返回。

static int __driver_attach(struct device *dev, void *data) { struct device_driver *drv = data; /* * Lock device and try to bind to it. We drop the error * here and always return 0, because we need to keep trying * to bind to devices and some drivers will return an error * simply if it didn't support the device. * * driver_probe_device() will spit a warning if there * is an error. */ if (!driver_match_device(drv, dev)) return 0; if (dev->parent) /* Needed for USB */ down(&dev->parent->sem); down(&dev->sem); if (!dev->driver) driver_probe_device(drv, dev); up(&dev->sem); if (dev->parent) up(&dev->parent->sem); return 0; }

匹配的时候调用的bus的match函数。

struct bus_type platform_bus_type = { .name = "platform", .dev_attrs = platform_dev_attrs, .match = platform_match, .uevent = platform_uevent, .pm = PLATFORM_PM_OPS_PTR, };

找到platform_match:

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); /* match against the id table first */ 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); }

最后一行可以看到通过pdev->name与drv->name进行匹配，也就是说是通过设备与驱动的名字进行匹配。匹配成功后调用驱动的probe函数。

int driver_probe_device(struct device_driver *drv, struct device *dev) { 。。。。。。。。。 ret = really_probe(dev, drv); 。。。。。。。。 } static int really_probe(struct device *dev, struct device_driver *drv) { 。。。。。。。。 if (dev->bus->probe) { ret = dev->bus->probe(dev); if (ret) goto probe_failed; } else if (drv->probe) { ret = drv->probe(dev); if (ret) goto probe_failed; } 。。。。。。。。 }

由relly_probe函数可以看出，如果bus定义了probe函数，则调用bus的probe函数；如果bus，没有定义而driver定义了probe函数，则调用driver的probe函数。由上边的platform_bus_type可以看出bus并没有定义probe函数，所以调用driver的probe函数。

测试程序：

device.c

#include <linux/module.h> #include <linux/init.h> #include <linux/device.h> #include <linux/string.h> #include <linux/module.h> #include <linux/platform_device.h> static struct platform_device *my_device; static int __init platform_dev_init(void) { int ret; //分配结构 my_device = platform_device_alloc("my_dev", -1); //注册设备 ret = platform_device_add(my_device); if(ret) printk("platform_device_add failed!\n"); return ret; } static void __exit platform_dev_exit(void) { platform_device_unregister(my_device);//卸载设备 } module_init(platform_dev_init); module_exit(platform_dev_exit); MODULE_LICENSE("GPL");

driver.c

#include <linux/module.h> #include <linux/kernel.h> #include <linux/init.h> #include <linux/device.h> #include <linux/string.h> #include <linux/module.h> #include <linux/platform_device.h> static int my_probe(struct device *dev) { printk("Driver found device!\n"); return 0; } static int my_remove(struct device *dev) { printk("Driver found device unpluged!\n"); return 0; } //定义platform_driver结构体 static struct platform_driver my_driver = { .probe = my_probe, .remove = my_remove, .driver = { .owner = THIS_MODULE, .name = "my_dev", }, }; static int __init my_driver_init(void) { return platform_driver_register(&my_driver); } static void __exit my_driver_exit(void) { platform_driver_unregister(&my_driver); } module_init(my_driver_init); module_exit(my_driver_exit); MODULE_LICENSE("GPL");

测试效果：

root@hacker:/home/hacker/platform# insmod driver.ko root@hacker:/home/hacker/platform# insmod device.ko root@hacker:/home/hacker/platform# dmesg [ 4499.724439] Driver found device! root@hacker:/home/hacker/platform# rmmod driver.ko root@hacker:/home/hacker/platform# dmesg [ 4499.724439] Driver found device! [ 4513.368712] Driver found device unpluged! root@hacker:/home/hacker/platform# rmmod device.ko root@hacker:/home/hacker/platform# insmod device.ko root@hacker:/home/hacker/platform# insmod driver.ko root@hacker:/home/hacker/platform# dmesg [ 4540.509227] Driver found device! root@hacker:/home/hacker/platform# rmmod device.ko root@hacker:/home/hacker/platform# dmesg [ 4540.509227] Driver found device! [ 4545.786076] Driver found device unpluged! root@hacker:/home/hacker/platform# rmmod driver.ko root@hacker:/home/hacker/platform# dmesg [ 4540.509227] Driver found device! [ 4545.786076] Driver found device unpluged!

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