platform总线：是管理片上资源的虚拟总线

• platform组成：
  • 1.platform_device： 描述与硬件相关信息的数据结构体
  • 2.platform_driver： 描述与硬件无关的数据结构体
  • 3.platform_bus_type：管理和匹配platform_device和platform_driver

基础驱动模型：

• 1.device
• 2.device_driver
• 3.bus_type
• 4.class

基础驱动模型的设计初衷是实现硬件与驱动的分离，使得linux实现跨平台的特性。基础驱动模型应用于内核的各种框架和总线

其他驱动： other drivers

/**
 * struct device_driver - The basic device driver structure
 * @name:   Name of the device driver.
 * @bus:    The bus which the device of this driver belongs to.
 * @owner:  The module owner.
 * @mod_name:   Used for built-in modules.
 * @suppress_bind_attrs: Disables bind/unbind via sysfs.
 * @of_match_table: The open firmware table.
 * @acpi_match_table: The ACPI match table.
 * @probe:  Called to query the existence of a specific device,
 *      whether this driver can work with it, and bind the driver
 *      to a specific device.
 * @remove: Called when the device is removed from the system to
 *      unbind a device from this driver.
 * @shutdown:   Called at shut-down time to quiesce the device.
 * @suspend:    Called to put the device to sleep mode. Usually to a
 *      low power state.
 * @resume: Called to bring a device from sleep mode.
 * @groups: Default attributes that get created by the driver core
 *      automatically.
 * @pm:     Power management operations of the device which matched
 *      this driver.
 * @p:      Driver core's private data, no one other than the driver
 *      core can touch this.
 *
 * The device driver-model tracks all of the drivers known to the system.
* The main reason for this tracking is to enable the driver core to match
 * up drivers with new devices. Once drivers are known objects within the
 * system, however, a number of other things become possible. Device drivers
 * can export information and configuration variables that are independent
 * of any specific device.
 */
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;
};


/**
 * struct device - The basic device structure
 * @parent: The device's "parent" device, the device to which it is attached.
 *      In most cases, a parent device is some sort of bus or host
 *      controller. If parent is NULL, the device, is a top-level device,
 *      which is not usually what you want.
 * @p:      Holds the private data of the driver core portions of the device.
 *      See the comment of the struct device_private for detail.
 * @kobj:   A top-level, abstract class from which other classes are derived.
 * @init_name:  Initial name of the device.
 * @type:   The type of device.
 *      This identifies the device type and carries type-specific
 *      information.
 * @mutex:  Mutex to synchronize calls to its driver.
 * @bus:    Type of bus device is on.
 * @driver: Which driver has allocated this
 * @platform_data: Platform data specific to the device.
 *      Example: For devices on custom boards, as typical of embedded
 *      and SOC based hardware, Linux often uses platform_data to point
 *      to board-specific structures describing devices and how they
 *      are wired.  That can include what ports are available, chip
 *      variants, which GPIO pins act in what additional roles, and so
 *      on.  This shrinks the "Board Support Packages" (BSPs) and
 *      minimizes board-specific #ifdefs in drivers.
 * @power:  For device power management.
 *      See Documentation/power/devices.txt for details.
 * @pm_domain:  Provide callbacks that are executed during system suspend,
 *      hibernation, system resume and during runtime PM transitions
 *      along with subsystem-level and driver-level callbacks.
 * @pins:   For device pin management.
 *      See Documentation/pinctrl.txt for details.
 * @numa_node:  NUMA node this device is close to.
 * @dma_mask:   Dma mask (if dma'ble device).
 * @coherent_dma_mask: Like dma_mask, but for alloc_coherent mapping as not all
 *      hardware supports 64-bit addresses for consistent allocations
 *      such descriptors.
 * @dma_parms:  A low level driver may set these to teach IOMMU code about
 *      segment limitations.
 * @dma_pools:  Dma pools (if dma'ble device).
 * @dma_mem:    Internal for coherent mem override.
 * @cma_area:   Contiguous memory area for dma allocations
 * @archdata:   For arch-specific additions.
 * @of_node:    Associated device tree node.
 * @acpi_node:  Associated ACPI device node.
 * @devt:   For creating the sysfs "dev".
 * @id:     device instance
 * @devres_lock: Spinlock to protect the resource of the device.
 * @devres_head: The resources list of the device.
 * @knode_class: The node used to add the device to the class list.
 * @class:  The class of the device.
 * @groups: Optional attribute groups.
 * @release:    Callback to free the device after all references have
*      gone away. This should be set by the allocator of the
 *      device (i.e. the bus driver that discovered the device).
 * @iommu_group: IOMMU group the device belongs to.
 *
 * @offline_disabled: If set, the device is permanently online.
 * @offline:    Set after successful invocation of bus type's .offline().
 *
 * At the lowest level, every device in a Linux system is represented by an
 * instance of struct device. The device structure contains the information
 * that the device model core needs to model the system. Most subsystems,
 * however, track additional information about the devices they host. As a
 * result, it is rare for devices to be represented by bare device structures;
 * instead, that structure, like kobject structures, is usually embedded within
 * a higher-level representation of the device.
 */
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 */
    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_DMA_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;

    bool            offline_disabled:1;
    bool            offline:1;
};


/**
 * struct bus_type - The bus type of the device
 *
 * @name:   The name of the bus.
 * @dev_name:   Used for subsystems to enumerate devices like ("foo%u", dev->id).
 * @dev_root:   Default device to use as the parent.
 * @dev_attrs:  Default attributes of the devices on the bus.
 * @bus_groups: Default attributes of the bus.
 * @dev_groups: Default attributes of the devices on the bus.
 * @drv_groups: Default attributes of the device drivers on the bus.
 * @match:  Called, perhaps multiple times, whenever a new device or driver
 *      is added for this bus. It should return a nonzero value if the
 *      given device can be handled by the given driver.
 * @uevent: Called when a device is added, removed, or a few other things
 *      that generate uevents to add the environment variables.
 * @probe:  Called when a new device or driver add to this bus, and callback
 *      the specific driver's probe to initial the matched device.
 * @remove: Called when a device removed from this bus.
 * @shutdown:   Called at shut-down time to quiesce the device.
 *
 * @online: Called to put the device back online (after offlining it).
 * @offline:    Called to put the device offline for hot-removal. May fail.
 *
 * @suspend:    Called when a device on this bus wants to go to sleep mode.
 * @resume: Called to bring a device on this bus out of sleep mode.
 * @pm:     Power management operations of this bus, callback the specific
 *      device driver's pm-ops.
 * @iommu_ops:  IOMMU specific operations for this bus, used to attach IOMMU
 *              driver implementations to a bus and allow the driver to do
 *              bus-specific setup
 * @p:      The private data of the driver core, only the driver core can
 *      touch this.
 * @lock_key:   Lock class key for use by the lock validator
 *
 * A bus is a channel between the processor and one or more devices. For the
 * purposes of the device model, all devices are connected via a bus, even if
 * it is an internal, virtual, "platform" bus. Buses can plug into each other.
 * A USB controller is usually a PCI device, for example. The device model
 * represents the actual connections between buses and the devices they control.
 * A bus is represented by the bus_type structure. It contains the name, the
 * default attributes, the bus' methods, PM operations, and the driver core's
 * private data.
 */
struct bus_type {
    const char      *name;
    const char      *dev_name;
    struct device       *dev_root;
    struct device_attribute *dev_attrs; /* use dev_groups instead */
    const struct attribute_group **bus_groups;
    const struct attribute_group **dev_groups;
    const struct attribute_group **drv_groups;

    int (*match)(struct device *dev, struct device_driver *drv);
    int (*uevent)(struct device *dev, struct kobj_uevent_env *env);
    int (*probe)(struct device *dev);
    int (*remove)(struct device *dev);
    void (*shutdown)(struct device *dev);

    int (*online)(struct device *dev);
    int (*offline)(struct device *dev);

    int (*suspend)(struct device *dev, pm_message_t state);
    int (*resume)(struct device *dev);

    const struct dev_pm_ops *pm;

    struct iommu_ops *iommu_ops;

    struct subsys_private *p;
    struct lock_class_key lock_key;
};

struct platform_driver {
    int (*probe)(struct platform_device *);//当platform_driver和platform_device匹配成功时，此函数将自动执行，一般在probe函数中实现driver的初始化程序设计
    int (*remove)(struct platform_device *); //当platform_driver和platform_device从匹配状态分离时，此函数将自动执行，所以我们将注销和释放的动作放在此函数中实现
    void (*shutdown)(struct platform_device *); //电源管理回调函数
    int (*suspend)(struct platform_device *, pm_message_t state);//电源管理回调函数
    int (*resume)(struct platform_device *); //电源管理回调函数
    struct device_driver driver;//内嵌的基础驱动模型
    const struct platform_device_id *id_table;//设备id匹配的标识
    bool prevent_deferred_probe; //匹配尝试的次数
};

/**
 * 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.
 */
此函数是platform_bus_type中实现platform_driver和platform_device的关键函数：


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 *///先尝试设备树风格的匹配
    if (of_driver_match_device(dev, drv))
        return 1;

    /* Then try ACPI style match *///再尝试ACPI风格的匹配
    if (acpi_driver_match_device(dev, drv))
        return 1;
   /* Then try to match against the id table *///再尝试设备id风格的匹配
    if (pdrv->id_table)
        return platform_match_id(pdrv->id_table, pdev) != NULL;

    /* fall-back to driver name match */ //尝试设备名称匹配
    return (strcmp(pdev->name, drv->name) == 0);
}

struct platform_device {
    const char  *name;  //是设备名称，是platform_device和platform_driver名字匹配的标识
    int     id;    //设备id
    bool        id_auto; //设备id自动赋值
    struct device   dev; //内嵌的基础驱动模型
    u32     num_resources; //描述硬件资源的个数
    struct resource *resource; //描述硬件资源的数据结构体

    const struct platform_device_id *id_entry; //设备id属性

    /* MFD cell pointer */
    struct mfd_cell *mfd_cell; //多功能设备属性

    /* arch specific additions */
    struct pdev_archdata    archdata; //平台私有数据
};

/*************************************************************************/
/**
 * platform_device_register - add a platform-level device
 * @pdev: platform device we're adding
 */
int platform_device_register(struct platform_device *pdev)
函数功能： 向内核注册platform_device
返回值：  成功为0，失败返回负数
参数1：   要注册的platform_device结构体指针
/*************************************************************************/

/*************************************************************************/
/**
 * platform_device_unregister - unregister a platform-level device
 * @pdev: platform device we're unregistering
 *
 * Unregistration is done in 2 steps. First we release all resources
 * and remove it from the subsystem, then we drop reference count by
 * calling platform_device_put().
 */
void platform_device_unregister(struct platform_device *pdev)
函数功能： 从内核注销platform_device
返回值：  无
参数1：   要注销的platform_device结构体指针
/*************************************************************************/

/*************************************************************************/
/*
 * use a macro to avoid include chaining to get THIS_MODULE
 */
#define platform_driver_register(drv) \
    __platform_driver_register(drv, THIS_MODULE)
函数功能： 向内核注册platform_driver
返回值：  无
参数1：   要注册的platform_driver结构体指针
/*************************************************************************/

/*************************************************************************/
/**
 * platform_driver_unregister - unregister a driver for platform-level devices
 * @drv: platform driver structure
 */
void platform_driver_unregister(struct platform_driver *drv)
函数功能： 从内核注销platform_driver
返回值：  无
参数1：   要注销的platform_driver结构体指针
/*******************************************1******************************/