《linux设备驱动开发详解》笔记——12linux设备驱动的软件架构思想

　　本章重点讲解思想、思想、思想。

12.1 linux驱动的软件架构

　　下述三种思想，在linux的spi、iic、usb等复杂驱动里广泛使用。后面几节分别对这些思想进行详细说明。

• 思想1：驱动与设备分离，linux采用总线、设备和驱动模型，驱动只管驱动，设备只管设备，总线负责匹配设备和驱动；驱动从标准途径拿到板级信息（设备信息，现在都已dts的形式存在），这样驱动就可以放之四海而皆准了，结构如下图。

　　　说到“总线”，有很多种，如I2C、SPI等，linux还为没有硬件总线的设备提出一种虚拟总线，即platform总线，同时还有对应的platform设备和platform驱动。

　　

　　为啥？ linux驱动要支持很多硬件，如果把设备信息写到驱动里，驱动会有非常多分支，一堆东西揉到一起，换成一锅粥，所以要把设备和驱动分开。

• 思想2：分层设计思想，file_opretations、IO模型等，是很多驱动共有的部分，linux提炼出一个中间层，把这些部分封装起来，供所有驱动使用。这就引出了软件分层的思想。

• 思想3：主机与外设分隔的思想。例如spi分为主机和外设，不同CPU有M种spi主机，同时不通外设也有N种，如果直接交叉支持，势必有M*N种组合，代码会非常复杂。需要在主机和外设中间插入一个标准API，把M和N分隔开，主机和外设都使用标准API与中间的分隔层接口，这样只需要实现M个主机和N个外设驱动即可，这种思想也叫“高内聚，低耦合”

     

12.2 platform设备驱动

12.2.1  platform总线、设备与驱动

• linux 2.6以后，采用总线、设备、驱动模型；
• platform的引入：有些设备本身依附一种总线，例如IIC、SPI、PCI、SPI等，很容易实现linux的总线/设备/驱动模型；但有些设备不依赖总线，例如SOC系统内部集成的独立外设控制器等，基于这种情况，linux发明了一种虚拟总线，即platform总线，对应的设备和驱动分别为platform_device和platform_driver。
• platform device不是针对linux的字符设备、块设备、网络设备的，是linux的一种附加手段。SOC内部集成的各控制器，例如IIC、RTC、LCD等一般都归纳为platform device。
• platform作为一种虚拟总线，与其他实体总线地位对等，例如SPI/IIC总线等，掌握了platform总线，其他总线也是类似的。

　　关键数据结构：

　　1. device

#include <linux/platform_device.h>

struct platform_device {
    const char    *name;
    int        id;
    bool        id_auto;
    struct device    dev;　　　　　　　　　　// linux/device.h里定义，总线match时，实际match的是dev，所有设备共性的部分
    u32        num_resources;　　　　　　　　// 资源
    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;
};

2.driver

#include <linux/platform_device.h>

// probe等函数由内核的platform机制实现了，驱动需要填充driver结构体
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);　　// 电源管理，基本不用了，有driver里的
    int (*resume)(struct platform_device *);　　　　　　　　　　　　　　// 同上
    struct device_driver driver;　　　　　　　　　　　　　　　　　　　　　// 所有驱动共享的部分，match以后driver.probe执行，同时调用外层platform_driver的prove执行　　　　　　　　　　　　　　　
    const struct platform_device_id *id_table;　　　　　　　　　　　　  // 一组ID表
    bool prevent_deferred_probe;
};

// linux/device.h
/**
 * 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;　　　　　　　　　　　　　　// 对应总线结构体指针

    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);　　　　　        // 总线match完设备和驱动以后，这个函数会执行，
　　　　　　　　　　　　　　　  // 形参dev就是被match的设备信息！！！
    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;
};

3.总线

总线的类型为bus_type,内核直接为platform定义了一个总线实体

// drivers/base/platform.c，这些函数都是现成的，在platform机制里实现了。
struct bus_type platform_bus_type = {
    .name        = "platform",
    .dev_groups    = platform_dev_groups,
    .match        = platform_match,　　　　　　// 匹配函数，关键
    .uevent        = platform_uevent,
    .pm        = &platform_dev_pm_ops,
};

/**
 * 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.
 */
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 */　　// 基于dts匹配优先级最高
    if (of_driver_match_device(dev, drv))
        return ;

    /* Then try ACPI style match */　　
    if (acpi_driver_match_device(dev, drv))
        return ;

    /* Then try to match against the id table */　　　　// 基于platform device和platform driver的ID
    if (pdrv->id_table)
        return platform_match_id(pdrv->id_table, pdev) != NULL;

    /* fall-back to driver name match */　　　　// 基于名字
    return (strcmp(pdev->name, drv->name) == );
}

　　linux 2.6以及之前版本，platform device通常定义在板级bsp里，然后再add；而3.x以后，改为自动展开dts，形成若干device。

12.2.2 将globalmem作为platform设备

没法实验，只罗列代码。

static int globalfifo_probe(struct platform_device *pdev)　　　　// 完成原来globalmem_init的任务
{
    int ret;
    dev_t devno = MKDEV(globalfifo_major, );

    if (globalfifo_major)
        ret = register_chrdev_region(devno, , "globalfifo");
    else {
        ret = alloc_chrdev_region(&devno, , , "globalfifo");
        globalfifo_major = MAJOR(devno);
    }
    if (ret < )
        return ret;

    globalfifo_devp = devm_kzalloc(&pdev->dev, sizeof(*globalfifo_devp),GFP_KERNEL);
    if (!globalfifo_devp) {
        ret = -ENOMEM;
        goto fail_malloc;
    }

    globalfifo_setup_cdev(globalfifo_devp, );

    mutex_init(&globalfifo_devp->mutex);
    init_waitqueue_head(&globalfifo_devp->r_wait);
    init_waitqueue_head(&globalfifo_devp->w_wait);

    return ;

fail_malloc:
    unregister_chrdev_region(devno, );
    return ret;
}

static int globalfifo_remove(struct platform_device *pdev)　　　　// 完成原来globalmem_exit的任务
{
    cdev_del(&globalfifo_devp->cdev);
    unregister_chrdev_region(MKDEV(globalfifo_major, ), );

    return ;
}

static struct platform_driver globalfifo_driver = {
    .driver = {
        .name = "globalfifo",
        .owner = THIS_MODULE,
    },
    .probe = globalfifo_probe,
    .remove = globalfifo_remove,
};

module_platform_driver(globalfifo_driver);　　　　// !!!注册platform驱动，/sys/bus/platform/drivers/globalmem,多出一个globalmem子目录

// 在板级bsp里(arch/arm/mach-xxx/mach-yyy.c,xxx为SOC名，yyy为board名)增加platform device，
// 系统初始化时添加到系统里，/sys/device/platform/globalmem,多出一个globalmem子目录，该目录中有driver符号链接,
// 指向/sys/bus/platform/drivers/globalmem
static struct platform_device globalfifo_device = {
    .name = "globalfifo",
    .id = -,
};

12.2.3 platform设备资源和数据

在platform_device结构体中，有resource结构体，表示该device的资源，start和end随flag的变化而表示不同的含义：

flag：

• IORESOURCE_MEM，start和end表示platform device占据的开始开始地址和结束地址

• IORESOURCE_IRQ,start和end表示使用中断号的开始值和结束值，如果只有1个中断号，则开始值和结束值相同

resource在板级支持包或者dts里定义，dts的定义后续说明，板级支持包都淘汰了，不再说明。

   /* Resources are tree-like, allowing

  * nesting etc..
  */
struct resource {
    resource_size_t start;
    resource_size_t end;
    const char *name;
    unsigned long flags;
    struct resource *parent, *sibling, *child;
};

/*
 * IO resources have these defined flags.
 */
#define IORESOURCE_BITS        0x000000ff    /* Bus-specific bits */

#define IORESOURCE_TYPE_BITS    0x00001f00    /* Resource type */
#define IORESOURCE_IO        0x00000100    /* PCI/ISA I/O ports */
#define IORESOURCE_MEM        0x00000200
#define IORESOURCE_REG        0x00000300    /* Register offsets */
#define IORESOURCE_IRQ        0x00000400
#define IORESOURCE_DMA        0x00000800
#define IORESOURCE_BUS        0x00001000

#define IORESOURCE_PREFETCH    0x00002000    /* No side effects */
#define IORESOURCE_READONLY    0x00004000
#define IORESOURCE_CACHEABLE    0x00008000
#define IORESOURCE_RANGELENGTH    0x00010000
#define IORESOURCE_SHADOWABLE    0x00020000

#define IORESOURCE_SIZEALIGN    0x00040000    /* size indicates alignment */
#define IORESOURCE_STARTALIGN    0x00080000    /* start field is alignment */

#define IORESOURCE_MEM_64    0x00100000
#define IORESOURCE_WINDOW    0x00200000    /* forwarded by bridge */
#define IORESOURCE_MUXED    0x00400000    /* Resource is software muxed */

#define IORESOURCE_EXCLUSIVE    0x08000000    /* Userland may not map this resource */
#define IORESOURCE_DISABLED    0x10000000
#define IORESOURCE_UNSET    0x20000000
#define IORESOURCE_AUTO        0x40000000
#define IORESOURCE_BUSY        0x80000000    /* Driver has marked this resource busy */

/* PnP IRQ specific bits (IORESOURCE_BITS) */
#define IORESOURCE_IRQ_HIGHEDGE        (1<<0)
#define IORESOURCE_IRQ_LOWEDGE        (1<<1)
#define IORESOURCE_IRQ_HIGHLEVEL    (1<<2)
#define IORESOURCE_IRQ_LOWLEVEL        (1<<3)
#define IORESOURCE_IRQ_SHAREABLE    (1<<4)
#define IORESOURCE_IRQ_OPTIONAL     (1<<5)

/* PnP DMA specific bits (IORESOURCE_BITS) */
#define IORESOURCE_DMA_TYPE_MASK    (3<<0)
#define IORESOURCE_DMA_8BIT        (0<<0)
#define IORESOURCE_DMA_8AND16BIT    (1<<0)
#define IORESOURCE_DMA_16BIT        (2<<0)

#define IORESOURCE_DMA_MASTER        (1<<2)
#define IORESOURCE_DMA_BYTE        (1<<3)
#define IORESOURCE_DMA_WORD        (1<<4)

#define IORESOURCE_DMA_SPEED_MASK    (3<<6)
#define IORESOURCE_DMA_COMPATIBLE    (0<<6)
#define IORESOURCE_DMA_TYPEA        (1<<6)
#define IORESOURCE_DMA_TYPEB        (2<<6)
#define IORESOURCE_DMA_TYPEF        (3<<6)

/* PnP memory I/O specific bits (IORESOURCE_BITS) */
#define IORESOURCE_MEM_WRITEABLE    (1<<0)    /* dup: IORESOURCE_READONLY */
#define IORESOURCE_MEM_CACHEABLE    (1<<1)    /* dup: IORESOURCE_CACHEABLE */
#define IORESOURCE_MEM_RANGELENGTH    (1<<2)    /* dup: IORESOURCE_RANGELENGTH */
#define IORESOURCE_MEM_TYPE_MASK    (3<<3)
#define IORESOURCE_MEM_8BIT        (0<<3)
#define IORESOURCE_MEM_16BIT        (1<<3)
#define IORESOURCE_MEM_8AND16BIT    (2<<3)
#define IORESOURCE_MEM_32BIT        (3<<3)
#define IORESOURCE_MEM_SHADOWABLE    (1<<5)    /* dup: IORESOURCE_SHADOWABLE */
#define IORESOURCE_MEM_EXPANSIONROM    (1<<6)

/* PnP I/O specific bits (IORESOURCE_BITS) */
#define IORESOURCE_IO_16BIT_ADDR    (1<<0)
#define IORESOURCE_IO_FIXED        (1<<1)

/* PCI ROM control bits (IORESOURCE_BITS) */
#define IORESOURCE_ROM_ENABLE        (1<<0)    /* ROM is enabled, same as PCI_ROM_ADDRESS_ENABLE */
#define IORESOURCE_ROM_SHADOW        (1<<1)    /* ROM is copy at C000:0 */
#define IORESOURCE_ROM_COPY        (1<<2)    /* ROM is alloc'd copy, resource field overlaid */
#define IORESOURCE_ROM_BIOS_COPY    (1<<3)    /* ROM is BIOS copy, resource field overlaid */

/* PCI control bits.  Shares IORESOURCE_BITS with above PCI ROM.  */
#define IORESOURCE_PCI_FIXED        (1<<4)    /* Do not move resource */

12.3 设备驱动的分层思想

稍后具体分析1个linux的驱动比较好。

12.4 主机驱动与外设驱动分离的设计思想

核心是定义好外设与主机之间的标准API，两边都使用标准API。具体分析一个驱动，便于理解。

12.5 总结

掌握思想，用这些思想去分析具体驱动，多读读驱动，慢慢就能理解这些思想了。