我们接着来到s3cmci.c文件
s3cmci_init----->platform_driver_register(&s3cmci_driver_2440)------------>s3cmci_probe_2440----->s3cmci_probe
在s3cmci_probe中主要是分配及初始化
struct mmc_host *mmc;
struct s3cmci_host *host;
这两个结构体。分配DMA通道，注册irq中断。
以下对个别函数的作用进行说明：
1: clk_get
系统初始化的时候外围总线上的设备不是都给时钟的，主要是为了省电。
在2.6.20中，我们在文件arch/arm/mach-s3c2410/s3c2410-clock中可以看到nand,sdi,adc,i2c,iis这些是不给时钟的
lcd,gpio,usb,uart这些是给时钟的
clk_get在arch/arm/mach-s3c2410/clock.c中定义
2: mmc_alloc_host
mmc_alloc_host分配sizeof(struct mmc_host)+extra这么大的空间，并做以下初始化
host = mmc_alloc_host_sysfs(extra, dev);
host->parent = dev;
host->class_dev.parent = dev;
host->class_dev.class = &mmc_host_class;
device_initialize(&host->class_dev);
spin_lock_init(&host->lock);
init_waitqueue_head(&host->wq);
INIT_LIST_HEAD(&host->cards);
INIT_DELAYED_WORK(&host->detect, mmc_rescan);
* By default, hosts do not support SGIO or large requests.
* They have to set these according to their abilities.
host->max_hw_segs = 1;
host->max_phys_segs = 1;
host->max_sectors = 1 << (PAGE_CACHE_SHIFT - 9);
host->max_seg_size = PAGE_CACHE_SIZE;
3:
mmc_add_host
调用mmc_add_host的最终结果是device_add(&host->class->dev)(所以在/sys/class/mmc/目录下出现mmc0文件)。
并会调用mmc_power_off(host);mmc_detect_change(host, 0);
mmc_power_off函数比较简单，顾名思义，它是让SD/MMC卡停止工作的，相应的，此函数就会配置相应的IO口以及时钟等。
我们来看看mmc_detect_change函数吧。
void mmc_detect_change(struct mmc_host *host, unsigned long delay)
{
mmc_schedule_delayed_work(&host->detect, delay);
}
int mmc_schedule_delayed_work(struct delayed_work *work, unsigned long delay)
{
return queue_delayed_work(workqueue, work, delay);
}
queue_delayed_work把host->detect提交到workqueue工作对列中。
相应定义：
INIT_DELAYED_WORK(&host->detect, mmc_rescan);
workqueue = create_singlethread_workqueue("kmmcd");
所以，当此delayed_work执行的时候，mmc_rescan将会被调用
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static void mmc_rescan(struct work_struct *work)
{
struct mmc_host *host =
container_of(work, struct mmc_host, detect.work);//返回指向s3cmci_probe中分配的mmc_host结构的指针
struct list_head *l, *n;
unsigned char power_mode;
mmc_claim_host(host);
/*
驱动中使用mmc_claim_host(host);来得知,当前mmc控制器是否被占用,当前mmc控制器如果被占用,那么 host->claimed = 1;否则为0,如果为1,那么会在for(;;)循环中调用schedule切换出自己,当占用mmc控制器的操作完成之后,执行 mmc_release_host()的时候,会激活登记到等待队列&host->wq中的其他程序获得mmc主控制器的物理使用权
*/
/*
* Check for removed cards and newly inserted ones. We check for
* removed cards first so we can intelligently re-select the VDD.
*/
power_mode = host->ios.power_mode;
if (power_mode == MMC_POWER_ON)
mmc_check_cards(host);
mmc_setup(host);
/*
* Some broken cards process CMD1 even in stand-by state. There is
* no reply, but an ILLEGAL_COMMAND error is cached and returned
* after next command. We poll for card status here to clear any
* possibly pending error.
*/
if (power_mode == MMC_POWER_ON)
mmc_check_cards(host);
if (!list_empty(&host->cards)) {
/*
* (Re-)calculate the fastest clock rate which the
* attached cards and the host support.
*/
host->ios.clock = mmc_calculate_clock(host);
mmc_set_ios(host);
}
mmc_release_host(host);
list_for_each_safe(l, n, &host->cards) {
struct mmc_card *card = mmc_list_to_card(l);
/*
* If this is a new and good card, register it.
*/
if (!mmc_card_present(card) && !mmc_card_dead(card)) {
if (mmc_register_card(card))
mmc_card_set_dead(card);
else
mmc_card_set_present(card);
}
/*s
* If this card is dead, destroy it.
*/
if (mmc_card_dead(card)) {
list_del(&card->node);
mmc_remove_card(card);
}
}
/*
* If we discover that there are no cards on the
* bus, turn off the clock and power down.
*/
if (list_empty(&host->cards))
mmc_power_off(host);
}
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起初，power_mode = MMC_POWER_OFF，故第一个mmc_check_cards(host)是不会执行的。但mmc_setup函数中设置了power_mode = MMC_POWER_ON。故第二个mmc_check_cards(host)是会执行的。
在mmc_setup中，会调用mmc_discover_cards.如果发现有卡，则add new card to list.
因为现在没有发现卡,host->card=NULL,故mmc_check_cards与mmc_rescan中的list_for_each_safe循环体中的内容也是不会执行的。
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static void mmc_check_cards(struct mmc_host *host)
{
struct list_head *l, *n;
mmc_deselect_cards(host);// Ensure that no card is selected.
list_for_each_safe(l, n, &host->cards) {
struct mmc_card *card = mmc_list_to_card(l);
struct mmc_command cmd;
int err;
cmd.opcode = MMC_SEND_STATUS;
cmd.arg = card->rca << 16;
cmd.flags = MMC_RSP_R1 | MMC_CMD_AC;
err = mmc_wait_for_cmd(host, &cmd, CMD_RETRIES);
if (err == MMC_ERR_NONE)
continue;
mmc_card_set_dead(card);
}
}
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执行完s3cmci_probe后，在终端会有以下信息：
s3c2410-sdi s3c2410-sdi: powered down.
s3c2410-sdi s3c2410-sdi: initialisation done.
s3c2410-sdi s3c2410-sdi: running at 0kHz (requested: 0kHz).
s3c2410-sdi s3c2410-sdi: running at 198kHz (requested: 197kHz).
s3c2410-sdi s3c2410-sdi: running at 198kHz (requested: 197kHz).
s3c2410-sdi s3c2410-sdi: running at 198kHz (requested: 197kHz).
s3c2410-sdi s3c2410-sdi: CMD[TIMEOUT] #2 op:APP_CMD(55) arg:0x00000000 flags:0xe
s3c2410-sdi s3c2410-sdi: CMD[TIMEOUT] #3 op:APP_CMD(55) arg:0x00000000 flags:0xe
s3c2410-sdi s3c2410-sdi: CMD[TIMEOUT] #4 op:APP_CMD(55) arg:0x00000000 flags:0xe
s3c2410-sdi s3c2410-sdi: CMD[TIMEOUT] #5 op:APP_CMD(55) arg:0x00000000 flags:0xe
s3c2410-sdi s3c2410-sdi: CMD[TIMEOUT] #6 op:ALL_SEND_OCR(1) arg:0x00000000 flage
s3c2410-sdi s3c2410-sdi: powered down.
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