平臺總線和IIC，SPI，IIS都是總線類型，一般的，總線下，掛載對應的設備。但實際上，設備要正常運轉，是需要驅動程序來未知提供驅動的。所以linux內核也把驅動掛載在對應的總線下。總線，驅動，設備三者缺一不可.
相應的，內核衍生出來的平臺總線，那麼便衍生出來了平臺設備和憑條驅動。他們均有自己的專屬函數來註冊，註銷。這個是成一套體系結構的.在以後的驅動開發中，很是常見與重要.
一)內核中的總線,設備,驅動
1)總線
struct bus_type {
const char *name;
const char *dev_name;
struct device *dev_root;
struct bus_attribute *bus_attrs;//總線屬性
struct device_attribute *dev_attrs;//設備屬性
struct driver_attribute *drv_attrs;//驅動屬性
int (*match)(struct device *dev, struct device_driver *drv);//匹配總線下的設備和驅動
int (*uevent)(struct device *dev, struct kobj_uevent_env *env);//用於總線環境變量的添加
int (*probe)(struct device *dev);//回調函數
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 dev_pm_ops *pm;//電源管理
struct iommu_ops *iommu_ops;
struct subsys_private *p;//將bus device sysfs聯繫起來
struct lock_class_key lock_key;
};
註冊：bus_register(struct bus_type *bus);
註銷：bus_unregister(struct bus_type *bus);2)設備
struct device {
struct device *parent;
struct device_private *p;
struct kobject kobj;
const char *init_name; /* initial name of the device */
const struct device_type *type;
struct mutex mutex; /* mutex to synchronize calls to
* its driver.
*/
struct bus_type *bus; /* type of bus device is on 設備所屬的總線*/
struct device_driver *driver; /* which driver has allocated this
device */
void *platform_data; /* Platform specific data, device
core doesn't touch it */
struct dev_pm_info power;
struct dev_pm_domain *pm_domain;
#ifdef CONFIG_PINCTRL
struct dev_pin_info *pins;
#endif
#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 device_dma_parameters *dma_parms;
struct list_head dma_pools; /* dma pools (if dma'ble) */
struct dma_coherent_mem *dma_mem; /* internal for coherent mem
override */
#ifdef CONFIG_CMA
struct cma *cma_area; /* contiguous memory area for dma
allocations */
#endif
/* arch specific additions */
struct dev_archdata archdata;
struct device_node *of_node; /* associated device tree node */
struct acpi_dev_node acpi_node; /* associated ACPI device node */
dev_t devt; /* dev_t, creates the sysfs "dev" */
u32 id; /* device instance */
spinlock_t devres_lock;
struct list_head devres_head;
struct klist_node knode_class;
struct class *class;
const struct attribute_group **groups; /* optional groups */
void (*release)(struct device *dev);
struct iommu_group *iommu_group;
};
設備註冊：int device_register(struct device *dev)
設備註銷：void device_unregister(struct device *dev)3)設備驅動
struct device_driver {
const char *name;
struct bus_type *bus;//掛載的總線，所屬的總線
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);// 設備match到驅動，則調用對應驅動的probe函數，驅動設備
int (*remove) (struct device *dev);//當驅動或者設備被卸載，則調用對應驅動的remove函數
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;
};
驅動註冊：int driver_register(struct device_driver *drv)
驅動註銷：void driver_unregister(struct device_driver *drv)
二)平臺設備總線
總線：
struct bus_type platform_bus_type = {
.name = "platform",
.dev_attrs = platform_dev_attrs,
.match = platform_match,
.uevent = platform_uevent,
.pm = &platform_dev_pm_ops,
};
設備：
struct platform_device {
const char *name;
int id;
bool id_auto;
struct device dev;
u32 num_resources;
struct resource *resource;
const struct platform_device_id *id_entry;
/* MFD cell pointer */
struct mfd_cell *mfd_cell;
/* arch specific additions */
struct pdev_archdata archdata;
};
平臺設備的註冊：platform_device_register(struct platform_device * pdev)
平臺設備的註銷：platform_device_unregister(struct platform_device * pdev)驅動：
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;
};
平臺驅動的註冊：int platform_driver_register(struct platform_driver *drv)
平臺驅動的註銷：void platform_driver_unregister(struct platform_driver *drv)平臺設備匹配的流程：
先插入一個函數，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);
/* Attempt an OF style match first */
if (of_driver_match_device(dev, drv))
return 1;
/* Then try ACPI style match */
if (acpi_driver_match_device(dev, drv))
return 1;
/* Then try to match against the id table */
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);
}
//match 的方式：不同的內核，可能有所不同：我的內核版本：3.10.46
1.OF style match first
2.ACPI style match
3.match against the id table
4.driver name match大概的匹配流程：
1)平臺設備註冊流程：
platform_device_register()
{
--->platform_device_add()
{
--->device_add()
{
--->device_add()
{
--->bus_probe_device()
{
--->device_attach()
{
--->bus_for_each_drv(dev->bus, NULL, dev, __device_attach)
{
--->__device_attach()
{
--->driver_match_device()//platform_match()
//當match到驅動後，繼續下面步驟：
--->driver_probe_device()
{
--->really_probe()
{
--->drv->probe()//調用對應驅動的probe函數
}
}
}
}
}
}
}
}
}
}2)平臺驅動註冊流程：
platform_driver_register()
{
--->driver_register()
{
--->bus_add_driver()
{
--->driver_attach()
{
--->bus_for_each_dev(drv->bus, NULL, drv, __driver_attach)
{
--->__driver_attach()
{
--->driver_match_device()//platform_match()
//當match到對應的設備後，繼續
--->driver_probe_device()
{
--->really_probe()
{
--->drv->probe()//調用當前註冊驅動的probe函數
}
}
}
}
}
}
}
}
1.設備向對應平臺bus註冊設備，設備掛載到平臺bus下面的dev list鏈表中.
2.驅動向對應平臺bus註冊驅動，驅動掛載到平臺bus下面的driver list鏈表中.
3.設備和對應總線下的driver list鏈表中每個driver進行匹配(match).匹配成功則調用對應driver的probe函數，否則匹配失敗，則設備無法被驅動，設備無法工作.
match函數已經在上面列出。它有自己的匹配規則，上一篇的實例是按照match name來進行匹配的.
當設備或者驅動被卸載時，驅動的remove函數都會被調用.
平臺設備總線的意義：移植性強。通過我們是不需要寫平臺設備文件的，只需要寫對應的驅動文件。而驅動文件一般移植時並不需要修改。只需要修改對應的platform_data 平臺數據和resource 平臺資源列表便可.
這樣修改一個驅動或者移植一個驅動到另一個內核便變得很簡單。
