结构体内的#define宏定义

今儿看sd卡驱动看到一个结构体

struct mmc_host {

struct device *parent;

struct device class_dev;

int index;

const struct mmc_host_ops *ops;

unsigned int f_min;

unsigned int f_max;

u32 ocr_avail;

#define MMC_VDD_165_195 0x00000080 /* VDD voltage 1.65 - 1.95 */

#define MMC_VDD_20_21 0x00000100 /* VDD voltage 2.0 ~ 2.1 */

#define MMC_VDD_21_22 0x00000200 /* VDD voltage 2.1 ~ 2.2 */

#define MMC_VDD_22_23 0x00000400 /* VDD voltage 2.2 ~ 2.3 */

#define MMC_VDD_23_24 0x00000800 /* VDD voltage 2.3 ~ 2.4 */

#define MMC_VDD_24_25 0x00001000 /* VDD voltage 2.4 ~ 2.5 */

#define MMC_VDD_25_26 0x00002000 /* VDD voltage 2.5 ~ 2.6 */

#define MMC_VDD_26_27 0x00004000 /* VDD voltage 2.6 ~ 2.7 */

#define MMC_VDD_27_28 0x00008000 /* VDD voltage 2.7 ~ 2.8 */

#define MMC_VDD_28_29 0x00010000 /* VDD voltage 2.8 ~ 2.9 */

#define MMC_VDD_29_30 0x00020000 /* VDD voltage 2.9 ~ 3.0 */

#define MMC_VDD_30_31 0x00040000 /* VDD voltage 3.0 ~ 3.1 */

#define MMC_VDD_31_32 0x00080000 /* VDD voltage 3.1 ~ 3.2 */

#define MMC_VDD_32_33 0x00100000 /* VDD voltage 3.2 ~ 3.3 */

#define MMC_VDD_33_34 0x00200000 /* VDD voltage 3.3 ~ 3.4 */

#define MMC_VDD_34_35 0x00400000 /* VDD voltage 3.4 ~ 3.5 */

#define MMC_VDD_35_36 0x00800000 /* VDD voltage 3.5 ~ 3.6 */

unsigned long caps; /* Host capabilities */

#define MMC_CAP_4_BIT_DATA (1 << 0) /* Can the host do 4 bit transfers */

#define MMC_CAP_MMC_HIGHSPEED (1 << 1) /* Can do MMC high-speed timing */

#define MMC_CAP_SD_HIGHSPEED (1 << 2) /* Can do SD high-speed timing */

#define MMC_CAP_SDIO_IRQ (1 << 3) /* Can signal pending SDIO IRQs */

#define MMC_CAP_SPI (1 << 4) /* Talks only SPI protocols */

#define MMC_CAP_NEEDS_POLL (1 << 5) /* Needs polling for card-detection */

#define MMC_CAP_8_BIT_DATA (1 << 6) /* Can the host do 8 bit transfers */

#define MMC_CAP_DISABLE (1 << 7) /* Can the host be disabled */

#define MMC_CAP_NONREMOVABLE (1 << 8) /* Nonremovable e.g. eMMC */

#define MMC_CAP_WAIT_WHILE_BUSY (1 << 9) /* Waits while card is busy */

/* host specific block data */

unsigned int max_seg_size; /* see blk_queue_max_segment_size */

unsigned short max_hw_segs; /* see blk_queue_max_hw_segments */

unsigned short max_phys_segs; /* see blk_queue_max_phys_segments */

unsigned short unused;

unsigned int max_req_size; /* maximum number of bytes in one req */

unsigned int max_blk_size; /* maximum size of one mmc block */

unsigned int max_blk_count; /* maximum number of blocks in one req */

/* private data */

spinlock_t lock; /* lock for claim and bus ops */

struct mmc_ios ios; /* current io bus settings */

u32 ocr; /* the current OCR setting */

/* group bitfields together to minimize padding */

unsigned int use_spi_crc:1;

unsigned int claimed:1; /* host exclusively claimed */

unsigned int bus_dead:1; /* bus has been released */

#ifdef CONFIG_MMC_DEBUG

unsigned int removed:1; /* host is being removed */

#endif

/* Only used with MMC_CAP_DISABLE */

int enabled; /* host is enabled */

int nesting_cnt; /* "enable" nesting count */

int en_dis_recurs; /* detect recursion */

unsigned int disable_delay; /* disable delay in msecs */

struct delayed_work disable; /* disabling work */

struct mmc_card *card; /* device attached to this host */

wait_queue_head_t wq;

struct task_struct *claimer; /* task that has host claimed */

int claim_cnt; /* "claim" nesting count */

struct delayed_work detect;

const struct mmc_bus_ops *bus_ops; /* current bus driver */

unsigned int bus_refs; /* reference counter */

unsigned int bus_resume_flags;

#define MMC_BUSRESUME_MANUAL_RESUME (1 << 0)

#define MMC_BUSRESUME_NEEDS_RESUME (1 << 1)

unsigned int sdio_irqs;

struct task_struct *sdio_irq_thread;

atomic_t sdio_irq_thread_abort;

#ifdef CONFIG_LEDS_TRIGGERS

struct led_trigger *led; /* activity led */

#endif

struct dentry *debugfs_root;

#ifdef CONFIG_MMC_EMBEDDED_SDIO

struct {

struct sdio_cis *cis;

struct sdio_cccr *cccr;

struct sdio_embedded_func *funcs;

int num_funcs;

} embedded_sdio_data;

#endif

unsigned long private[0] ____cacheline_aligned;

};

在结构体内定义宏，啥意思？查一下：

关于宏的作用域

1.     宏没有可见域。

        如果说有，那就是从本文件（包括被包含的文件）中，该宏定义处开始，至文件的尾部或取消宏(#undef)为止。

2.     考虑一种特殊情况：

        一个宏定义，如果写在结构体之内，即使与结构体之外的宏定义名字重复了最多是编译警告。可是如果不在结构体之内，名字重复可肯定是error。（未证实，可以做实验，而且可以把两处的宏定义成不同的值，会是什么情况？）

        定义在结构体之内的宏在结构体内可以隐藏定义在结构体之外定义的宏，如果都在结构体之外定义，那么就是定义了两个相同的宏，而一个在内，一个在外，则结构体内只看到内部定义的宏，而结构体外只看到外部定义的宏，跟变量的隐藏类似。

    宏的处理是在编译的预处理阶段完成的。预处理器根本就不认识什么结构体，在C语言编译器编译这个C文件中的结构体时，这个define语句已经不存在了。相应的，用到这个宏的地方，宏本身也已经替换成宏的值（这个宏展开）。大家可以用gcc -E命令来只做预处理而不编译，看看出来后的文件。

    至于为什么在结构体里头#deifne，是因为这个宏一般用于定义该结构体里头的标志位变量的可能的值，和结构体的这个变量密切相关。放在一起从逻辑上比较容易理解。