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分类: LINUX

2009-11-02 09:33:24

Linux操作系统中,驱动程序的加载分为两种:内核启动时自动加载和用户手动加载;硬件设备也可以采用两种方式添加到系统中:在系统启动前及系统运行时的热插拨。下面,我们以arm体系结构下的at91处理器中的I2C控制器为例,介绍一下硬件设备及相关的驱动程序是如何绑定及松绑的。

1.      平台驱动注册过程

1.1 at91_i2c_init()函数

在文件drivers/i2c/busses/i2c-at91.c中,定义了结构体struct platform_driver并进行了初始化,通过使用module_init()宏进行声明,当模块被加载到内核时会调用 at91_i2c_init()函数。在此函数中,调用了platform_driver_register()函数来完成注册。

static struct platform_driver at91_i2c_driver = {

    .probe     = at91_i2c_probe,

    .remove       = __devexit_p(at91_i2c_remove),

    .suspend   = at91_i2c_suspend,

    .resume       = at91_i2c_resume,

    .driver       = {

       .name = "at91_i2c",

       .owner = THIS_MODULE,

    },

};

static int __init at91_i2c_init(void)

{

    return platform_driver_register(&at91_i2c_driver);

}

1.2 platform_driver_register()函数

在文件drivers/base/platform.c中,实现并导出了platform_driver_register()函数,以便使其他模块中的函数可以调用此函数。它在完成简单的包装后,调用了driver_register()函数,完成了从平台实现到Linux内核实现的过渡。

    在此,我们需要关注一下platform_match()platform_drv_probe()函数。platform_match() 函数确定驱动与设备的关联,而platform_drv_probe()函数会在随后介绍的函数中被调用。

//比较驱动信息中的name与设备信息中的name两者是否一致

static int platform_match(struct device * dev, struct device_driver * drv)

{

struct platform_device *pdev = container_of(dev, struct platform_device, dev);

    return (strncmp(pdev->name, drv->name, BUS_ID_SIZE) == 0);

}

struct bus_type platform_bus_type = {

    .name      = "platform",

    .dev_attrs = platform_dev_attrs,

    .match     = platform_match,

    .uevent       = platform_uevent,

    .suspend   = platform_suspend,

    .suspend_late = platform_suspend_late,

    .resume_early = platform_resume_early,

    .resume       = platform_resume,

};

EXPORT_SYMBOL_GPL(platform_bus_type);

/**

* platform_driver_register

* @drv: platform driver structure

*/

int platform_driver_register(struct platform_driver *drv)

{

    drv->driver.bus = &platform_bus_type;

    //really_probe函数中,回调了platform_drv_probe函数

    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;

    if (drv->suspend)

       drv->driver.suspend = platform_drv_suspend;

    if (drv->resume)

       drv->driver.resume = platform_drv_resume;

    return driver_register(&drv->driver);

}

EXPORT_SYMBOL_GPL(platform_driver_register);

1.3 driver_register()函数

在文件drivers/base/driver.c中,实现了driver_register()函数。在此函数中,初始化结构体struct device_driver中的klist_deviceunloaded字段,通过klist_device字段,可以保存此驱动支持的设备链表,通过完成接口机制,完成线程间的同步。链表和完成接口的详细信息可以参考文献[1]。返回bus_add_driver()函数的运行结果。

/**

* driver_register - register driver with bus

* @drv: driver to register

*

* We pass off most of the work to the bus_add_driver() call,

* since most of the things we have to do deal with the bus

* structures.

*

* The one interesting aspect is that we setup @drv->unloaded

* as a completion that gets complete when the driver reference

* count reaches 0.

*/

int driver_register(struct device_driver * drv)

{

    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);

    }

    klist_init(&drv->klist_devices, NULL, NULL);

    init_completion(&drv->unloaded);

    return bus_add_driver(drv);

}

1.4 bus_add_driver()函数

在文件drivers/base/bus.c中实现了bus_add_driver()函数,它通过语句klist_add_tail(&drv->knode_bus, &bus->klist_drivers); 将驱动信息保存到总线结构中,在设备注册过程中,我们就可以明白此语句的作用了。在此语句之前,调用了driver_attach()函数。

/**

* bus_add_driver - Add a driver to the bus.

* @drv: driver.

*

*/

int bus_add_driver(struct device_driver *drv)

{

    struct bus_type * bus = get_bus(drv->bus);

    int error = 0;

    if (!bus)

       return 0;

    pr_debug("bus %s: add driver %s\n", bus->name, drv->name);

    error = kobject_set_name(&drv->kobj, "%s", drv->name);

    if (error)

       goto out_put_bus;

    drv->kobj.kset = &bus->drivers;

    if ((error = kobject_register(&drv->kobj)))

       goto out_put_bus;

    error = driver_attach(drv);

    if (error)

       goto out_unregister;

    klist_add_tail(&drv->knode_bus, &bus->klist_drivers);

    module_add_driver(drv->owner, drv);

    error = driver_add_attrs(bus, drv);

    if (error) {

       /* How the hell do we get out of this pickle? Give up */

       printk(KERN_ERR "%s: driver_add_attrs(%s) failed\n",

           __FUNCTION__, drv->name);

    }

    error = add_bind_files(drv);

    if (error) {

       /* Ditto */

       printk(KERN_ERR "%s: add_bind_files(%s) failed\n",

           __FUNCTION__, drv->name);

    }

    return error;

out_unregister:

    kobject_unregister(&drv->kobj);

out_put_bus:

    put_bus(bus);

    return error;

}

1.5 dd.c文件

在文件drivers/base/dd.c中,实现了设备与驱动交互的核心函数。

1.5.1 driver_attach()函数

函数driver_attach()返回bus_for_each_dev()函数的运行结果。bus_for_each_dev()函数的原型如下:

int bus_for_each_dev(struct bus_type *bus, struct device *start, void *data,

    int (*fn) (struct device *, void *));

该函数迭代了在总线上的每个设备,将相关的device结构传递给fn,同时传递data值。如果startNULL,将从总线上的第一个设备开始迭代;否则将从start后的第一个设备开始迭代。如果fn返回一个非零值,将停止迭代,而这个值也会从该函数返回(摘自<设备驱动程序>>第三版)。

该函数是如何知道总线上的每个设备的呢?在设备注册过程中,我会详细介绍。

/*

* drivers/base/dd.c - The core device/driver interactions.

*

* This file contains the (sometimes tricky) code that controls the

* interactions between devices and drivers, which primarily includes

* driver binding and unbinding.

*/

/**

* driver_attach - try to bind driver to devices.

* @drv: driver.

*

* Walk the list of devices that the bus has on it and try to

* match the driver with each one. If driver_probe_device()

* returns 0 and the @dev->driver is set, we've found a

* compatible pair.

*/

int driver_attach(struct device_driver * drv)

{

    return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);

}

1.5.2 __driver_attach()函数

函数__driver_attach()在调用driver_probe_device()函数前,需要进行线程间的互斥处理。

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 (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;

}

1.5.3 driver_probe_device()函数

driver_probe_device()函数中,调用了match函数platform_match(),如果它返回0,表示驱动与设备不一致,函数返回;否则,调用really_probe()函数。

/**

* driver_probe_device - attempt to bind device & driver together

* @drv: driver to bind a device to

* @dev: device to try to bind to the driver

*

* First, we call the bus's match function, if one present, which should

* compare the device IDs the driver supports with the device IDs of the

* device. Note we don't do this ourselves because we don't know the

* format of the ID structures, nor what is to be considered a match and

* what is not.

*

* This function returns 1 if a match is found, an error if one occurs

* (that is not -ENODEV or -ENXIO), and 0 otherwise.

*

* This function must be called with @dev->sem held. When called for a

* USB interface, @dev->parent->sem must be held as well.

*/

int driver_probe_device(struct device_driver * drv, struct device * dev)

{

    struct stupid_thread_structure *data;

    struct task_struct *probe_task;

    int ret = 0;

    if (!device_is_registered(dev))

       return -ENODEV;

    if (drv->bus->match && !drv->bus->match(dev, drv))

       goto done;

    pr_debug("%s: Matched Device %s with Driver %s\n",

       drv->bus->name, dev->bus_id, drv->name);

    data = kmalloc(sizeof(*data), GFP_KERNEL);

    if (!data)

       return -ENOMEM;

    data->drv = drv;

    data->dev = dev;

    if (drv->multithread_probe) {

       probe_task = kthread_run(really_probe, data,

                  "probe-%s", dev->bus_id);

       if (IS_ERR(probe_task))

           ret = really_probe(data);

    } else

       ret = really_probe(data);

done:

    return ret;

}

struct stupid_thread_structure {

    struct device_driver *drv;

    struct device *dev;

};

1.5.4 really_probe()函数

really_probe()函数中,实现了设备与驱动的绑定。语句如下:dev->driver = drv;

ret = drv->probe(dev); probe()函数的实现如下:

include/linux/platform_device.h

#define to_platform_device(x) container_of((x), struct platform_device, dev)

drivers/base/platform.c

#define to_platform_driver(drv) (container_of((drv), struct platform_driver, driver))

static int platform_drv_probe(struct device *_dev)

{

    struct platform_driver *drv = to_platform_driver(_dev->driver);

    struct platform_device *dev = to_platform_device(_dev);

    return drv->probe(dev);

}

在此函数中,回调了我们在i2c-at91.c文件中实现的探测函数at91_i2c_probe(),至此,平台驱动的注册过程结束。

static atomic_t probe_count = ATOMIC_INIT(0);

static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue);

static int really_probe(void *void_data)

{

    struct stupid_thread_structure *data = void_data;

    struct device_driver *drv = data->drv;

    struct device *dev = data->dev;

    int ret = 0;

    atomic_inc(&probe_count);

    pr_debug("%s: Probing driver %s with device %s\n",

       drv->bus->name, drv->name, dev->bus_id);

    WARN_ON(!list_empty(&dev->devres_head));

    dev->driver = drv;

    if (driver_sysfs_add(dev)) {

       printk(KERN_ERR "%s: driver_sysfs_add(%s) failed\n",

           __FUNCTION__, dev->bus_id);

       goto probe_failed;

    }

    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;

    }

    //设备与驱动绑定后,对系统中已注册的组件进行事件通知。

    driver_bound(dev);

    ret = 1;

    pr_debug("%s: Bound Device %s to Driver %s\n",

       drv->bus->name, dev->bus_id, drv->name);

    goto done;

probe_failed:

    devres_release_all(dev);

    driver_sysfs_remove(dev);

    dev->driver = NULL;

    if (ret != -ENODEV && ret != -ENXIO) {

       /* driver matched but the probe failed */

       printk(KERN_WARNING

              "%s: probe of %s failed with error %d\n",

              drv->name, dev->bus_id, ret);

    }

    /*

    * Ignore errors returned by ->probe so that the next driver can try

    * its luck.

    */

    ret = 0;

done:

    kfree(data);

    atomic_dec(&probe_count);

    wake_up(&probe_waitqueue);

    return ret;

}

1.      平台驱动卸载过程

平台驱动卸载过程是注册的逆过程,详细信息可参考注册过程进行分析。

2.1 at91_i2c_exit()函数

static void __exit at91_i2c_exit(void)

{

    platform_driver_unregister(&at91_i2c_driver);

}

2.2 platform_driver_unregister()函数

/**

* platform_driver_unregister

* @drv: platform driver structure

*/

void platform_driver_unregister(struct platform_driver *drv)

{

    driver_unregister(&drv->driver);

}

EXPORT_SYMBOL_GPL(platform_driver_unregister);

2.3 driver_unregister()函数

/**

* driver_unregister - remove driver from system.

* @drv: driver.

*

* Again, we pass off most of the work to the bus-level call.

*

* Though, once that is done, we wait until @drv->unloaded is completed.

* This will block until the driver refcount reaches 0, and it is

* released. Only modular drivers will call this function, and we

* have to guarantee that it won't complete, letting the driver

* unload until all references are gone.

*/

void driver_unregister(struct device_driver * drv)

{

    bus_remove_driver(drv);

    /*

    * If the driver is a module, we are probably in

    * the module unload path, and we want to wait

    * for everything to unload before we can actually

    * finish the unload.

    */

    if (drv->owner)

       wait_for_completion(&drv->unloaded);

}

2.4 bus_remove_driver()函数

/**

* bus_remove_driver - delete driver from bus's knowledge.

* @drv: driver.

*

* Detach the driver from the devices it controls, and remove

* it from its bus's list of drivers. Finally, we drop the reference

* to the bus we took in bus_add_driver().

*/

void bus_remove_driver(struct device_driver * drv)

{

    if (!drv->bus)

       return;

    remove_bind_files(drv);

    driver_remove_attrs(drv->bus, drv);

    klist_remove(&drv->knode_bus);

    pr_debug("bus %s: remove driver %s\n", drv->bus->name, drv->name);

    driver_detach(drv);

    module_remove_driver(drv);

    kobject_unregister(&drv->kobj);

    put_bus(drv->bus);

}

2.5 driver_detach()函数

/**

* driver_detach - detach driver from all devices it controls.

* @drv: driver.

*/

void driver_detach(struct device_driver * drv)

{

    struct device * dev;

    for (;;) {

       spin_lock(&drv->klist_devices.k_lock);

       if (list_empty(&drv->klist_devices.k_list)) {

           spin_unlock(&drv->klist_devices.k_lock);

           break;

       }

       dev = list_entry(drv->klist_devices.k_list.prev,

              struct device, knode_driver.n_node);

       get_device(dev);

       spin_unlock(&drv->klist_devices.k_lock);

       if (dev->parent) /* Needed for USB */

           down(&dev->parent->sem);

       down(&dev->sem);

       if (dev->driver == drv)

           __device_release_driver(dev);

       up(&dev->sem);

       if (dev->parent)

           up(&dev->parent->sem);

       put_device(dev);

    }

}

2.6 __device_release_driver()函数

/**

* device_release_driver - manually detach device from driver.

* @dev: device.

*

* Manually detach device from driver.

*

* __device_release_driver() must be called with @dev->sem held.

* When called for a USB interface, @dev->parent->sem must be held

* as well.

*/

static void __device_release_driver(struct device * dev)

{

    struct device_driver * drv;

    drv = dev->driver;

    if (drv) {

       get_driver(drv);

       driver_sysfs_remove(dev);

       sysfs_remove_link(&dev->kobj, "driver");

       klist_remove(&dev->knode_driver);

       if (dev->bus)

           blocking_notifier_call_chain(&dev->bus->bus_notifier,

                          BUS_NOTIFY_UNBIND_DRIVER,

                          dev);

       if (dev->bus && dev->bus->remove)

           dev->bus->remove(dev);

       else if (drv->remove)

           drv->remove(dev);

       devres_release_all(dev);

       dev->driver = NULL;

       put_driver(drv);

    }

}

2.7 platform_drv_remove()函数

static int platform_drv_remove(struct device *_dev)

{

    struct platform_driver *drv = to_platform_driver(_dev->driver);

    struct platform_device *dev = to_platform_device(_dev);

    return drv->remove(dev);

}

在此函数中,回调了我们在i2c-at91.c文件中实现的移除函数at91_i2c_remove(),至此,平台驱动的卸载过程结束。

在注册和卸载过程中,Linux采用了一些变量来保存相关的信息,比如引用计数、通知链等,感兴趣的人员,可以详细的阅读此部分内容。

3.      设备注册过程

3.1 at91_add_device_i2c()函数

在文件arch/arm/mach-at91/at91sam9263_devices.c中,对I2C设备进行了定义。

/* --------------------------------------------------------------------

* TWI (i2c)

* -------------------------------------------------------------------- */

#if defined(CONFIG_I2C_AT91) || defined(CONFIG_I2C_AT91_MODULE)

static struct resource twi_resources[] = {

    [0] = {

       .start = AT91SAM9263_BASE_TWI,

       .end   = AT91SAM9263_BASE_TWI + SZ_16K - 1,

       .flags = IORESOURCE_MEM,

    },

    [1] = {

       .start = AT91SAM9263_ID_TWI,

       .end   = AT91SAM9263_ID_TWI,

       .flags = IORESOURCE_IRQ,

    },

};

static struct platform_device at91sam9263_twi_device = {

    //此名字与驱动信息中的名字"at91_i2c"是一致的,在match()函数调用中,会返回1

    .name      = "at91_i2c",

    .id    = -1,

    .resource = twi_resources,

    .num_resources    = ARRAY_SIZE(twi_resources),

};

void __init at91_add_device_i2c(void)

{

    /* pins used for TWI interface */

    at91_set_A_periph(AT91_PIN_PB4, 0);       /* TWD */

    at91_set_multi_drive(AT91_PIN_PB4, 1);

    at91_set_A_periph(AT91_PIN_PB5, 0);       /* TWCK */

    at91_set_multi_drive(AT91_PIN_PB5, 1);

    //对设备进行注册

    platform_device_register(&at91sam9263_twi_device);

}

#else

void __init at91_add_device_i2c(void) {}

#endif

3.2 platform.c文件

在文件drivers/base/platform.c中,实现了下面的函数。

3.2.1 platform_device_register()函数

/**

* platform_device_register - add a platform-level device

* @pdev: platform device we're adding

*

*/

int platform_device_register(struct platform_device * pdev)

{

    device_initialize(&pdev->dev);

    return platform_device_add(pdev);

}

EXPORT_SYMBOL_GPL(platform_device_register);




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