platform_driver,plateform_device,device,driver,net_device

 

 

内核中的platform driver机制需要将设备本身的资源注册进内核，由内核统一管理，在驱动程序中使用这些资源时通过platform device提供的标准接口进行申请并使用。这样可以提高驱动和资源管理的独立性。本文的目的就是希望弄清楚platform device和driver之间的关系。 1.1 相关数据结构 1.1.1 device 这个结构体定义为： struct device { struct klist klist_children; struct klist_node knode_parent; /* node in sibling list */ struct klist_node knode_driver; struct klist_node knode_bus; struct device *parent; struct kobject kobj; char bus_id[BUS_ID_SIZE]; /* position on parent bus */ struct device_type *type; unsigned is_registered:1; unsigned uevent_suppress:1; struct device_attribute uevent_attr; struct device_attribute *devt_attr; struct semaphore sem; /* semaphore to synchronize calls to * its driver. */ struct bus_type * bus; /* type of bus device is on */ struct device_driver *driver; /* which driver has allocated this device */ void *driver_data; /* data private to the driver */ void *platform_data; /* Platform specific data, device core doesn't touch it */ struct dev_pm_info power; #ifdef CONFIG_NUMA int numa_node; /* NUMA node this device is close to */ #endif u64 *dma_mask; /* dma mask (if dma'able device) */ u64 coherent_dma_mask;/* Like dma_mask, but for alloc_coherent mappings as not all hardware supports 64 bit addresses for consistent allocations such descriptors. */ struct list_head dma_pools; /* dma pools (if dma'ble) */ struct dma_coherent_mem *dma_mem; /* internal for coherent mem override */ /* arch specific additions */ struct dev_archdata archdata; spinlock_t devres_lock; struct list_head devres_head; /* class_device migration path */ struct list_head node; struct class *class; dev_t devt; /* dev_t, creates the sysfs "dev" */ struct attribute_group **groups; /* optional groups */ void (*release)(struct device * dev); }; 这个结构体有点复杂，不过我们暂时用不了这么多。 1.1.2 resource 这个结构体定义为： /* * Resources are tree-like, allowing * nesting etc.. */ struct resource { resource_size_t start; resource_size_t end; const char *name; unsigned long flags; struct resource *parent, *sibling, *child; }; 在这个结构体中，start和end的意义将根据flags中指定的资源类型进行解释。内核对资源进行了分类，一共有四种类型： #define IORESOURCE_IO 0x00000100 /* Resource type */ #define IORESOURCE_MEM 0x00000200 #define IORESOURCE_IRQ 0x00000400 #define IORESOURCE_DMA 0x00000800 对于DM9000来说，其定义的资源如下： static struct resource dm9000_bfin_resources[] = { { .start = 0x2C000000, .end = 0x2C000000 + 0x7F, .flags = IORESOURCE_MEM, }, { .start = IRQ_PF10, .end = IRQ_PF10, .flags = IORESOURCE_IRQ | IORESOURCE_IRQ_LOWLEVEL, }, }; 也就是说，它定义了两种类型的资源。从这里也可以看出resource结构体里面的name成员没有太大的用处。 1.1.3 platform_device 这个结构体定义为： struct platform_device { const char * name; u32 id; struct device dev; u32 num_resources; struct resource * resource; }; 它对device加了一层包装，添加了resource的内容。看看DM9000的定义： static struct platform_device dm9000_bfin_device = { .name = "dm9000", .id = -1, .num_resources = ARRAY_SIZE(dm9000_bfin_resources), .resource = dm9000_bfin_resources, }; 注意这里的name。 1.1.4 device_driver 这个结构体定义为： struct device_driver { const char * name; struct bus_type * bus; struct kobject kobj; struct klist klist_devices; struct klist_node knode_bus; struct module * owner; const char * mod_name; /* used for built-in modules */ struct module_kobject * mkobj; int (*probe) (struct device * dev); int (*remove) (struct device * dev); void (*shutdown) (struct device * dev); int (*suspend) (struct device * dev, pm_message_t state); int (*resume) (struct device * dev); }; 1.1.5 platform_driver 这个结构体定义为： 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; }; 它在device_driver的基础上封装了几个操作函数。 1.1.6 bus_type 这个结构体定义为： struct bus_type { const char * name; struct module * owner; struct kset subsys; struct kset drivers; struct kset devices; struct klist klist_devices; struct klist klist_drivers; struct blocking_notifier_head bus_notifier; struct bus_attribute * bus_attrs; struct device_attribute * dev_attrs; struct driver_attribute * drv_attrs; struct bus_attribute drivers_autoprobe_attr; struct bus_attribute drivers_probe_attr; int (*match)(struct device * dev, struct device_driver * drv); int (*uevent)(struct device *dev, char **envp, int num_envp, char *buffer, int buffer_size); int (*probe)(struct device * dev); int (*remove)(struct device * dev); void (*shutdown)(struct device * dev); int (*suspend)(struct device * dev, pm_message_t state); int (*suspend_late)(struct device * dev, pm_message_t state); int (*resume_early)(struct device * dev); int (*resume)(struct device * dev); unsigned int drivers_autoprobe:1; }; 1.2 资源注册 在arch/blackfin/mach-bf561/boards/ezkit.c中有这样的代码： static int __init ezkit_init(void) { int ret; printk(KERN_INFO "%s(): registering device resources/n", __func__); ret = platform_add_devices(ezkit_devices, ARRAY_SIZE(ezkit_devices)); if (ret < 0) return ret; return 0; } arch_initcall(ezkit_init); 这里使用了arch_initcall来对ezkit_init函数进行调用次序的限制，而驱动的加载通常是使用module_init进行限制的，因此ezkit_init函数将先于驱动加载。 在这里ezkit_devices的定义为： static struct platform_device *ezkit_devices[] __initdata = { &dm9000_bfin_device, ………… }; 1.2.1 platform_add_devices 这个函数比较简单： /** * platform_add_devices - add a numbers of platform devices * @devs: array of platform devices to add * @num: number of platform devices in array */ int platform_add_devices(struct platform_device **devs, int num) { int i, ret = 0; for (i = 0; i < num; i++) { ret = platform_device_register(devs[i]); if (ret) { while (--i >= 0) platform_device_unregister(devs[i]); break; } } return ret; } 为这个数组中的每个元素调用platform_device_register，如果出错则注销此前注册的所有platform device。 1.2.2 platform_device_register 这个函数的实现为： /** * 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); } 也比较简单，先调用device_initialize初始化platform_device::dev，这里仅仅是对device结构体的成员赋初值，略过它不做分析。接下来的关键是platform_device_add。 1.2.3 platform_device_add 这个函数定义为： /** * platform_device_add - add a platform device to device hierarchy * @pdev: platform device we're adding * * This is part 2 of platform_device_register(), though may be called * separately _iff_ pdev was allocated by platform_device_alloc(). */ 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; pdev->dev.bus = &platform_bus_type; if (pdev->id != -1) snprintf(pdev->dev.bus_id, BUS_ID_SIZE, "%s.%u", pdev->name, pdev->id); else strlcpy(pdev->dev.bus_id, pdev->name, BUS_ID_SIZE); for (i = 0; i < pdev->num_resources; i++) { struct resource *p, *r = &pdev->resource[i]; if (r->name == NULL) r->name = pdev->dev.bus_id; p = r->parent; if (!p) { if (r->flags & IORESOURCE_MEM) p = &iomem_resource; else if (r->flags & IORESOURCE_IO) p = &ioport_resource; } if (p && insert_resource(p, r)) { printk(KERN_ERR "%s: failed to claim resource %d/n", pdev->dev.bus_id, i); ret = -EBUSY; goto failed; } } pr_debug("Registering platform device '%s'. Parent at %s/n", pdev->dev.bus_id, pdev->dev.parent->bus_id); ret = device_add(&pdev->dev); if (ret == 0) return ret; failed: while (--i >= 0) if (pdev->resource[i].flags & (IORESOURCE_MEM|IORESOURCE_IO)) release_resource(&pdev->resource[i]); return ret; } 在这个函数里做了两件关键的事情，一个是注册device设备，它将device::bus指定为platform_bus_type。另一个是注册resource。看下面的这几行代码： if (!p) { if (r->flags & IORESOURCE_MEM) p = &iomem_resource; else if (r->flags & IORESOURCE_IO) p = &ioport_resource; } 对照DM9000的资源定义： static struct resource dm9000_bfin_resources[] = { { .start = 0x2C000000, .end = 0x2C000000 + 0x7F, .flags = IORESOURCE_MEM, }, { .start = IRQ_PF10, .end = IRQ_PF10, .flags = IORESOURCE_IRQ | IORESOURCE_IRQ_LOWLEVEL, }, }; 它的中断资源并没有进行注册。 1.2.4 device_add 这一函数定义为： /** * device_add - add device to device hierarchy. * @dev: device. * * This is part 2 of device_register(), though may be called * separately _iff_ device_initialize() has been called separately. * * This adds it to the kobject hierarchy via kobject_add(), adds it * to the global and sibling lists for the device, then * adds it to the other relevant subsystems of the driver model. */ int device_add(struct device *dev) { …………………….. if ((error = device_add_attrs(dev))) goto AttrsError; if ((error = device_pm_add(dev))) goto PMError; if ((error = bus_add_device(dev))) goto BusError; ………………….. } 这里有一个关键调用bus_add_device，它将把dev添加到platform_bus_type这一全局变量中的列表。 1.2.5 bus_add_device 这个函数定义为： /** * bus_add_device - add device to bus * @dev: device being added * * - Add the device to its bus's list of devices. * - Create link to device's bus. */ int bus_add_device(struct device * dev) { struct bus_type * bus = get_bus(dev->bus); int error = 0; if (bus) { pr_debug("bus %s: add device %s/n", bus->name, dev->bus_id); error = device_add_attrs(bus, dev); if (error) goto out_put; error = sysfs_create_link(&bus->devices.kobj, &dev->kobj, dev->bus_id); if (error) goto out_id; error = sysfs_create_link(&dev->kobj, &dev->bus->subsys.kobj, "subsystem"); if (error) goto out_subsys; error = make_deprecated_bus_links(dev); if (error) goto out_deprecated; } return 0; out_deprecated: sysfs_remove_link(&dev->kobj, "subsystem"); out_subsys: sysfs_remove_link(&bus->devices.kobj, dev->bus_id); out_id: device_remove_attrs(bus, dev); out_put: put_bus(dev->bus); return error; } 注意当执行到此函数时dev->bus指向platform_bus_type这一全局变量，因而这一函数将把dev添加到platform_bus_type的链表中。 1.3 驱动注册 下面是DM9000网卡的驱动加载代码： static int __init dm9000_init(void) { printk(KERN_INFO "%s Ethernet Driver/n", CARDNAME); return platform_driver_register(&dm9000_driver); /* search board and register */ } module_init(dm9000_init); 很简单的代码，直接调用platform_driver_register注册驱动，这里dm9000_driver的定义为： static struct platform_driver dm9000_driver = { .driver = { .name = "dm9000", .owner = THIS_MODULE, }, .probe = dm9000_probe, .remove = dm9000_drv_remove, .suspend = dm9000_drv_suspend, .resume = dm9000_drv_resume, }; 1.3.1 platform_driver_register 这个函数定义为： /** * platform_driver_register * @drv: platform driver structure */ int platform_driver_register(struct platform_driver *drv) { drv->driver.bus = &platform_bus_type; 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); } 注意由于DM9000的platform_driver中指定了probe，remove，suspend，resume这四个函数，因此device_driver结构体中的这几个函数指针将进行初始化设置。最后再调用driver_register注册driver成员，有点奇怪，怎么就抛弃了platform_driver呢？ 1.3.2 driver_register 这个函数定义为： /** * 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. */ 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); return bus_add_driver(drv); } 当函数执行到这里的时候，drv->bus指向的是platform_bus_type这一全局变量。 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, }; 1.3.3 bus_add_driver 这个函数定义为： /** * 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 -EINVAL; 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; if (drv->bus->drivers_autoprobe) { 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; } 当函数执行到此的时候，drv->bus将指向platform_bus_type这一全局变量，而这一全局变量的drivers_autoprobe成员在bus_register这一全局初始化函数中设置为1。因此这里将调用driver_attach函数，注意此时传递进去的参数drv指向的是dm9000_driver的driver成员。 1.3.4 driver_attach 这一函数定义为： /** * 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); } 很简单，转向bus_for_each_dev。 1.3.5 bus_for_each_dev 这一函数定义为： /** * bus_for_each_dev - device iterator. * @bus: bus type. * @start: device to start iterating from. * @data: data for the callback. * @fn: function to be called for each device. * * Iterate over @bus's list of devices, and call @fn for each, * passing it @data. If @start is not NULL, we use that device to * begin iterating from. * * We check the return of @fn each time. If it returns anything * other than 0, we break out and return that value. * * NOTE: The device that returns a non-zero value is not retained * in any way, nor is its refcount incremented. If the caller needs * to retain this data, it should do, and increment the reference * count in the supplied callback. */ int bus_for_each_dev(struct bus_type * bus, struct device * start, void * data, int (*fn)(struct device *, void *)) { struct klist_iter i; struct device * dev; int error = 0; if (!bus) return -EINVAL; klist_iter_init_node(&bus->klist_devices, &i, (start ? &start->knode_bus : NULL)); while ((dev = next_device(&i)) && !error) error = fn(dev, data); klist_iter_exit(&i); return error; } 简单枚举此总线上注册的device，然后为其调用__driver_attach函数，试图将一个device和传递进来的driver相匹配。 1.3.6 __driver_attach 这一函数定义为： 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; } 很简单，转而调用driver_probe_device进行驱动的匹配。 1.3.7 driver_probe_device 这个函数定义为： /** * 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, -ENODEV if the device is * not registered, 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) { 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); ret = really_probe(dev, drv); done: return ret; } 此时的drv->bus指向platform_bus_type这一全局变量，而它的match函数为platform_match，且让我们看看它是如何确定device和driver是否匹配的。 /** * platform_match - bind platform device to platform driver. * @dev: device. * @drv: driver. * * Platform device IDs are assumed to be encoded like this: * "<name><instance>", where <name> is a short description of the * type of device, like "pci" or "floppy", and <instance> is the * enumerated instance of the device, like '0' or '42'. * Driver IDs are simply "<name>". * So, extract the <name> from the platform_device structure, * and compare it against the name of the driver. Return whether * they match or not. */ 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); } 也就是说，它通过比较pdev->name和drv->name是否匹配来决定。 对于DM9000的驱动来说，这里的pdev指向dm9000_bfin_device，看看它的初始值： static struct platform_device dm9000_bfin_device = { .name = "dm9000", .id = -1, .num_resources = ARRAY_SIZE(dm9000_bfin_resources), .resource = dm9000_bfin_resources, }; 再看drv，其指向dm9000_driver这一变量中的driver成员。 static struct platform_driver dm9000_driver = { .driver = { .name = "dm9000", .owner = THIS_MODULE, }, .probe = dm9000_probe, .remove = dm9000_drv_remove, .suspend = dm9000_drv_suspend, .resume = dm9000_drv_resume, }; 在进行了正确的名称匹配之后，将调用really_probe进行硬件检测。 1.3.8 really_probe 这一函数定义为： static int really_probe(struct device *dev, struct device_driver *drv) { 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; } 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: atomic_dec(&probe_count); wake_up(&probe_waitqueue); return ret; } 此时的drv->bus指向platform_bus_type这一全局变量，其probe回调函数没有指定，而drv->probe函数则指向dm9000_probe。因此转向dm9000_probe执行，并将dm9000_bfin_device做为参数传递进去。 1.4 结论 platform device和driver分别向platform_bus_type这一中介注册，并通过名称进行相互间的匹配。很是有点婚姻中介的味道，还有点对暗号的神秘，呵呵！