Linux驱动修炼之道-platform
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：
hacker@hacker:~/linux-2.6.30.4$ cd /sys/bus/platform/hacker@hacker:/sys/bus/platform$ tree.|-- devices| |-- Fixed MDIO bus.0 -> ../../../devices/platform/Fixed MDIO bus.0| |-- eisa.0 -> ../../../devices/platform/eisa.0| |-- i8042 -> ../../../devices/platform/i8042| |-- pcspkr -> ../../../devices/platform/pcspkr| |-- rtc_cmos -> ../../../devices/platform/rtc_cmos| `-- serial8250 -> ../../../devices/platform/serial8250|-- drivers| |-- dsa| | |-- bind| | |-- uevent| | `-- unbind| |-- i8042| | |-- bind| | |-- i8042 -> ../../../../devices/platform/i8042| | |-- uevent| | `-- unbind| |-- mdio-gpio| | |-- bind| | |-- uevent| | `-- unbind| |-- parport_pc| | |-- bind| | |-- module -> ../../../../module/parport_pc| | |-- uevent| | `-- unbind| |-- rtc_cmos| | |-- bind| | |-- rtc_cmos -> ../../../../devices/platform/rtc_cmos| | |-- uevent| | `-- unbind| |-- serial8250| | |-- bind| | |-- serial8250 -> ../../../../devices/platform/serial8250| | |-- uevent| | `-- unbind| `-- twl4030_reg| |-- bind| |-- uevent| `-- unbind|-- drivers_autoprobe|-- drivers_probe`-- uevent19 directories, 24 files
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*/intid; /*设备编号，配合设备名使用*/ struct devicedev;u32num_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.koroot@hacker:/home/hacker/platform# insmod device.koroot@hacker:/home/hacker/platform# dmesg[ 4499.724439] Driver found device!root@hacker:/home/hacker/platform# rmmod driver.koroot@hacker:/home/hacker/platform# dmesg[ 4499.724439] Driver found device![ 4513.368712] Driver found device unpluged!root@hacker:/home/hacker/platform# rmmod device.koroot@hacker:/home/hacker/platform# insmod device.koroot@hacker:/home/hacker/platform# insmod driver.koroot@hacker:/home/hacker/platform# dmesg[ 4540.509227] Driver found device!root@hacker:/home/hacker/platform# rmmod device.koroot@hacker:/home/hacker/platform# dmesg[ 4540.509227] Driver found device![ 4545.786076] Driver found device unpluged!root@hacker:/home/hacker/platform# rmmod driver.koroot@hacker:/home/hacker/platform# dmesg[ 4540.509227] Driver found device![ 4545.786076] Driver found device unpluged!
页:
[1]