platform总线是一种虚拟的总线,相应的设备则为platform_device,而驱动则为platform_driver。Linux 2.6的设备驱动模型中,把I2C、RTC、LCD等都归纳为platform_device。
总线将设备和驱动绑定,在系统每注册一个设备的时候,会寻找与之匹配的驱动;相反的,在系统每注册一个驱动的时候,会寻找与之匹配的设备,而匹配由总线完成。
Linux2.6系统中定义了一个bus_type的实例platform_bus_type
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- struct bus_type platform_bus_type = {
- .name = "platform",
- .dev_attrs = platform_dev_attrs,
- .match = platform_match, //设备和驱动使用match函数来判断是否匹配
- .uevent = platform_uevent,
- .pm = PLATFORM_PM_OPS_PTR,
- };
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- /* platform_match函数用于匹配总线中的驱动和设备 */
- 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);
- }
platform_match函数首先判断是否由id_table,如果有则使用id_table来进行匹配,否则,判断platform_device和platform_driver成员里的name,如果二者的name字段相同则匹配,如果匹配则调用platform_driver的probe函数。
platform_device结构体的定义
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- struct platform_device {
- const char * name; /* 名字 */
- int id;
- struct device dev;
- u32 num_resources; /* 资源总数 */
- struct resource * resource; /* 资源 */
- struct platform_device_id *id_entry;
- };
其中有个重要的成员是resource,是设备的资源信息,如IO地址,中断号等。
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- struct resource {
- resource_size_t start; //资源的起始值
- resource_size_t end; //资源的结束值
- const char *name;
- unsigned long flags; //资源的类型,如IORESOURCE_IO,IORESOURCE_MEM,IORESOURCE_IRQ,IORESOURCE_DMA
- struct resource *parent, *sibling, *child;
- };
有的设备可能有多个资源,通常使用platform_get_resource函数来获取资源
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- /**
- * platform_get_resource - get a resource for a device
- * @dev: platform device
- * @type: resource type
- * @num: resource index
- */
- struct resource *platform_get_resource(struct platform_device *dev,
- unsigned int type, unsigned int num)
- {
- int i;
- for (i = 0; i < dev->num_resources; i++) {
- struct resource *r = &dev->resource[i];
- if (type == resource_type(r) && num-- == 0)
- return r;
- }
- return NULL;
- }
平台设备的注册,使用platform_device_register函数
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- int platform_device_register(struct platform_device *pdev)
- {
- device_initialize(&pdev->dev);
- return platform_device_add(pdev);
- }
platform_device_register函数先通过device_initialize函数初始化platform_device的device成员,然后调用platform_device_add向内核添加一个平台设备。
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- int platform_device_add(struct platform_device *pdev)
- {
- int i, ret = 0;
- if (!pdev) /* 如果pdev为空则返回EINVAL */
- return -EINVAL;
- /* 如果pdev->dev.parent为空则将pdev->dev.parent设置为platform_bus */
- if (!pdev->dev.parent)
- pdev->dev.parent = &platform_bus;
- pdev->dev.bus = &platform_bus_type; /* 设置总线类型 */
- if (pdev->id != -1) /* 如果id = -1则表示自动分配name */
- dev_set_name(&pdev->dev, "%s.%d", pdev->name, pdev->id);
- else
- dev_set_name(&pdev->dev, pdev->name);
- for (i = 0; i < pdev->num_resources; i++) {
- struct resource *p, *r = &pdev->resource[i]; /* 获取资源 */
- if (r->name == NULL)
- r->name = dev_name(&pdev->dev);
- p = r->parent;
- if (!p) {
- if (resource_type(r) == IORESOURCE_MEM) /* 设置资源类型 */
- 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));
- /* 向内核添加一个device */
- 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;
- }
platform_device_add最终调用device_add来完成平台设备的注册。
相反地,如果要注销平台设备则使用platform_device_unregister函数
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- void platform_device_unregister(struct platform_device *pdev)
- {
- platform_device_del(pdev);
- platform_device_put(pdev);
- }
platform_device_unregister函数调用platform_device_del函数来注销平台设备
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- void platform_device_del(struct platform_device *pdev)
- {
- int i;
- if (pdev) {
- device_del(&pdev->dev);
- for (i = 0; i < pdev->num_resources; i++) {
- struct resource *r = &pdev->resource[i];
- unsigned long type = resource_type(r);
- if (type == IORESOURCE_MEM || type == IORESOURCE_IO)
- release_resource(r);
- }
- }
- }
platform_device_del函数调用device_del函数来删除平台设备,相应地,要释放资源应调用release_resource函数,前提是资源的类型必须为IORESOURCE_MEM或者IORESOURCE_IO
platform_driver的定义:
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- 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;
- };
device_driver的定义:
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- struct device_driver {
- const char *name;
- struct bus_type *bus;
- struct module *owner;
- const char *mod_name; /* used for built-in modules */
- bool suppress_bind_attrs; /* disables bind/unbind via sysfs */
- const struct of_device_id *of_match_table;
- const struct acpi_device_id *acpi_match_table;
- 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);
- const struct attribute_group **groups;
- const struct dev_pm_ops *pm;
- struct driver_private *p;
- };
platform_driver结构体有device_driver成员,该成员的各自字段如上所示,device_driver也有probe、remove、shutdown等函数,在平台驱动注册的时候被初始化。
前面说过,当系统中存在有平台设备和平台驱动通过总线的match函数匹配后则会调用platform_driver的probe函数,参数为platform_device,有时候也通过id_table来判断是否匹配。
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- struct platform_device_id {
- char name[PLATFORM_NAME_SIZE];
- kernel_ulong_t driver_data
- __attribute__((aligned(sizeof(kernel_ulong_t))));
- };
平台驱动的注册使用platform_driver_register函数
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- 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);
- }
先初始化platform_driver里的driver,该driver的类型为device_driver,设置driver的bus为platform_bus_type;设置driver的probe为platform_drv_probe;设置driver的remove为platform_drv_remove;设置driver的shutdown为platform_drv_shutdown;设置driver的suspend为platform_drv_suspend;设置driver的resume为platform_drv_resume,最后调用driver_register函数来注册平台驱动。
相反地,要注销平台驱动的话,使用platform_driver_unregister函数
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- void platform_driver_unregister(struct platform_driver *drv)
- {
- driver_unregister(&drv->driver);
- }
附韦老师总结的bus_drv_dev模型的框架图