Linux平臺(tái)總線驅(qū)動(dòng)設(shè)備模型
platform總線是一種虛擬的總線，相應(yīng)的設(shè)備則為platform_device，而驅(qū)動(dòng)則為platform_driver。Linux 2.6的設(shè)備驅(qū)動(dòng)模型中，把I2C、RTC、LCD等都?xì)w納為platform_device。
總線將設(shè)備和驅(qū)動(dòng)綁定，在系統(tǒng)每注冊一個(gè)設(shè)備的時(shí)候，會(huì)尋找與之匹配的驅(qū)動(dòng);相反的，在系統(tǒng)每注冊一個(gè)驅(qū)動(dòng)的時(shí)候，會(huì)尋找與之匹配的設(shè)備，而匹配由總線完成。
Linux2.6系統(tǒng)中定義了一個(gè)bus_type的實(shí)例platform_bus_type
- struct bus_type platform_bus_type = {
- .name = "platform",
- .dev_attrs = platform_dev_attrs,
- .match = platform_match, //設(shè)備和驅(qū)動(dòng)使用match函數(shù)來判斷是否匹配
- .uevent = platform_uevent,
- .pm = PLATFORM_PM_OPS_PTR,
- };
- /* platform_match函數(shù)用于匹配總線中的驅(qū)動(dòng)和設(shè)備 */
- 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函數(shù)首先判斷是否由id_table，如果有則使用id_table來進(jìn)行匹配，否則，判斷platform_device和platform_driver成員里的name，如果二者的name字段相同則匹配，如果匹配則調(diào)用platform_driver的probe函數(shù)。
platform_device結(jié)構(gòu)體的定義
- struct platform_device {
- const char * name; /* 名字 */
- int id;
- struct device dev;
- u32 num_resources; /* 資源總數(shù) */
- struct resource * resource; /* 資源 */
- struct platform_device_id *id_entry;
- };
其中有個(gè)重要的成員是resource，是設(shè)備的資源信息，如IO地址，中斷號(hào)等。
- struct resource {
- resource_size_t start; //資源的起始值
- resource_size_t end; //資源的結(jié)束值
- const char *name;
- unsigned long flags; //資源的類型，如IORESOURCE_IO,IORESOURCE_MEM,IORESOURCE_IRQ,IORESOURCE_DMA
- struct resource *parent, *sibling, *child;
- };
有的設(shè)備可能有多個(gè)資源，通常使用platform_get_resource函數(shù)來獲取資源
- /**
- * 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;
- }
平臺(tái)設(shè)備的注冊，使用platform_device_register函數(shù)
- int platform_device_register(struct platform_device *pdev)
- {
- device_initialize(&pdev->dev);
- return platform_device_add(pdev);
- }
platform_device_register函數(shù)先通過device_initialize函數(shù)初始化platform_device的device成員，然后調(diào)用platform_device_add向內(nèi)核添加一個(gè)平臺(tái)設(shè)備。
- int platform_device_add(struct platform_device *pdev)
- {
- int i, ret = 0;
- if (!pdev) /* 如果pdev為空則返回EINVAL */
- return -EINVAL;
- /* 如果pdev->dev.parent為空則將pdev->dev.parent設(shè)置為platform_bus */
- if (!pdev->dev.parent)
- pdev->dev.parent = &platform_bus;
- pdev->dev.bus = &platform_bus_type; /* 設(shè)置總線類型 */
- if (pdev->id != -1) /* 如果id = -1則表示自動(dòng)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]; /* 獲取資源 */
- if (r->name == NULL)
- r->name = dev_name(&pdev->dev);
- p = r->parent;
- if (!p) {
- if (resource_type(r) == IORESOURCE_MEM) /* 設(shè)置資源類型 */
- 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));
- /* 向內(nèi)核添加一個(gè)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最終調(diào)用device_add來完成平臺(tái)設(shè)備的注冊。
相反地，如果要注銷平臺(tái)設(shè)備則使用platform_device_unregister函數(shù)
- void platform_device_unregister(struct platform_device *pdev)
- {
- platform_device_del(pdev);
- platform_device_put(pdev);
- }
platform_device_unregister函數(shù)調(diào)用platform_device_del函數(shù)來注銷平臺(tái)設(shè)備
- 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函數(shù)調(diào)用device_del函數(shù)來刪除平臺(tái)設(shè)備，相應(yīng)地，要釋放資源應(yīng)調(diào)用release_resource函數(shù)，前提是資源的類型必須為IORESOURCE_MEM或者IORESOURCE_IO
platform_driver的定義：
- 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的定義：
- 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結(jié)構(gòu)體有device_driver成員，該成員的各自字段如上所示，device_driver也有probe、remove、shutdown等函數(shù)，在平臺(tái)驅(qū)動(dòng)注冊的時(shí)候被初始化。
前面說過，當(dāng)系統(tǒng)中存在有平臺(tái)設(shè)備和平臺(tái)驅(qū)動(dòng)通過總線的match函數(shù)匹配后則會(huì)調(diào)用platform_driver的probe函數(shù)，參數(shù)為platform_device，有時(shí)候也通過id_table來判斷是否匹配。
- struct platform_device_id {
- char name[PLATFORM_NAME_SIZE];
- kernel_ulong_t driver_data
- __attribute__((aligned(sizeof(kernel_ulong_t))));
- };
平臺(tái)驅(qū)動(dòng)的注冊使用platform_driver_register函數(shù)
- 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，該driver的類型為device_driver，設(shè)置driver的bus為platform_bus_type;設(shè)置driver的probe為platform_drv_probe;設(shè)置driver的remove為platform_drv_remove;設(shè)置driver的shutdown為platform_drv_shutdown;設(shè)置driver的suspend為platform_drv_suspend;設(shè)置driver的resume為platform_drv_resume，***調(diào)用driver_register函數(shù)來注冊平臺(tái)驅(qū)動(dòng)。
相反地，要注銷平臺(tái)驅(qū)動(dòng)的話，使用platform_driver_unregister函數(shù)
- void platform_driver_unregister(struct platform_driver *drv)
- {
- driver_unregister(&drv->driver);
- }
