android底层开发入门(3)－Android Driver前篇

android是基于linux内核的操作系统，因此它能够在linux内核的基础上添加自己所特有的驱动程序，如power managerment模块

驱动最基础的几个部分：

• __init ***_init:模块被加载的时候调用
• __exit ***_exit:模块被卸载时调用
• module_init(***_init):向系统申明
• module_exit(***_exit):向系统申明

Driver的介绍

Driver是各种设备的实际控制者，他为kernel提供接口，使得kernel能够操作各种不同的硬件设备。

其源码在kernel/drivers/

Linux驱动程序模型是一个所有不同的驱动程序统一的模型。

当前驱动程序模型提供了一个通用的数据模型来描述总线和设备。统一的模型包括一组共同的属性,和一组常见的回调函数，来实现下列三个功能：

• 1，电源管理:suspend,resume…
• 2，即插即用设备支持:detect,match…
• 3，与用户空间的通信:sysfs,procfs…

那么驱动该是device的驱动，那么android又是咋么定义device的？

device.h

在这个文件中（kernel/include/linux/device.h），定义了device的设备（将其抽象化）·

其源码为：

/** * 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. * @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). * * 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_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;
};

列举出一部分源码的定义解释

• @name: 驱动名称
• @bus: 设备总线
• @of_match_table: 匹配表
• @acpi_match_table: 使用ACPI 方式的匹配表.
• @probe: 当一个设备与这个驱动匹配时被调用
• @remove: 当一个与这个驱动匹配的设备移除时被调用
• @shutdown: 关闭设备时调用
• @suspend: 设备休眠时调用
• @resume: 设备唤醒时调用
• @pm: 电源管理调用

以上我们可以看到device对应着一个实际或者虚拟的设备，是设备的抽象，我们先不详细地去看·

先来看一下device所定义的driver结构体

/** * 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 driver_private {
    struct kobject kobj;
    struct klist klist_devices;
    struct klist_node knode_bus;
    struct module_kobject *mkobj;
    struct device_driver *driver;
};

device_driver:
* @name: 驱动名称
* @bus: 设备总线
* @of_match_table: 匹配表
* @acpi_match_table: 使用ACPI 方式的匹配表.
* @probe: 当一个设备与这个驱动匹配时被调用
* @remove: 当一个与这个驱动匹配的设备移除时被调用
* @shutdown: 关闭设备时调用
* @suspend: 设备休眠时调用
* @resume: 设备唤醒时调用
* @pm: 电源管理调用

/** * 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. * @bus_attrs: Default attributes of the bus. * @dev_attrs: Default attributes of the devices on the bus. * @drv_attrs: 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. * @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. * * 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 bus_attribute    *bus_attrs;
    struct device_attribute *dev_attrs;
    struct driver_attribute *drv_attrs;

    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 (*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;
};

• @match:匹配总线中的dev和driver
• @uevent:用于总线对uevent的环境变量添加
• @probe:当一个总线上的设备或者驱动被添加时调用
• @remove:在总线上设备或者驱动要删除时调用
• @shutdown:在所有设备都关闭时调用
• @suspend:在总线上设备休眠时调用
• @resume:在总线上设备恢复时调用
• @pm:电源管理调用

bus是处理器与一个或者多个设备之间的通道

小结

可以看得出android是将设备抽象成各个结构体，然后各家厂商对接口实现就可以了·