驱动：
以SDIO为例其会采用mmc_attach_sdio来实现驱动和设备的匹配，其本质还是根据sdio_bus的匹配规则来实现匹配。在mmc_attach_sdio中首先是mmc匹配一个bus，即采用何种bus来进行mmc bus来处理host。在这里需要理解一点就是在SDIO中，对于SD卡存储器mmc为实体设备，而对于非SD卡存储器，如SDIO接口的设备，则mmc则表征为bus，这个比较重要。除了mmc bus外还存在SDIO_BUS。
/*
* Starting point for SDIO card init.
*/
int mmc_attach_sdio(struct mmc_host *host)
{
int err, i, funcs;
u32 ocr;
struct mmc_card *card;
BUG_ON(!host);
WARN_ON(!host->claimed);
err = mmc_send_io_op_cond(host, 0, &ocr);
if (err)
return err;
mmc_attach_bus(host, &mmc_sdio_ops);
if (host->ocr_avail_sdio)
host->ocr_avail = host->ocr_avail_sdio;
/*
* Sanity check the voltages that the card claims to
* support.
*/
if (ocr & 0x7F) {
pr_warning("%s: card claims to support voltages "
"below the defined range. These will be ignored.\n",
mmc_hostname(host));
ocr &= ~0x7F;
}
host->ocr = mmc_select_voltage(host, ocr);
/*
* Can we support the voltage(s) of the card(s)?
*/
if (!host->ocr) {
err = -EINVAL;
goto err;
}
/*
* Detect and init the card.
*/
err = mmc_sdio_init_card(host, host->ocr, NULL, 0);
if (err) {
if (err == -EAGAIN) {
/*
* Retry initialization with S18R set to 0.
*/
host->ocr &= ~R4_18V_PRESENT;
err = mmc_sdio_init_card(host, host->ocr, NULL, 0);
}
if (err)
goto err;
}
card = host->card;
/*
* Enable runtime PM only if supported by host+card+board
*/
if (host->caps & MMC_CAP_POWER_OFF_CARD) {
/*
* Let runtime PM core know our card is active
*/
err = pm_runtime_set_active(&card->dev);
if (err)
goto remove;
/*
* Enable runtime PM for this card
*/
pm_runtime_enable(&card->dev);
}
/*
* The number of functions on the card is encoded inside
* the ocr.
*/
funcs = (ocr & 0x70000000) >> 28;
card->sdio_funcs = 0;
#ifdef CONFIG_MMC_EMBEDDED_SDIO
if (host->embedded_sdio_data.funcs)
card->sdio_funcs = funcs = host->embedded_sdio_data.num_funcs;
#endif
/*
* Initialize (but don‘t add) all present functions.
*/
for (i = 0; i < funcs; i++, card->sdio_funcs++) {
#ifdef CONFIG_MMC_EMBEDDED_SDIO
if (host->embedded_sdio_data.funcs) {
struct sdio_func *tmp;
tmp = sdio_alloc_func(host->card);
if (IS_ERR(tmp))
goto remove;
tmp->num = (i + 1);
card->sdio_func[i] = tmp;
tmp->class = host->embedded_sdio_data.funcs[i].f_class;
tmp->max_blksize = host->embedded_sdio_data.funcs[i].f_maxblksize;
tmp->vendor = card->cis.vendor;
tmp->device = card->cis.device;
} else {
#endif
err = sdio_init_func(host->card, i + 1);
if (err)
goto remove;
#ifdef CONFIG_MMC_EMBEDDED_SDIO
}
#endif
/*
* Enable Runtime PM for this func (if supported)
*/
if (host->caps & MMC_CAP_POWER_OFF_CARD)
pm_runtime_enable(&card->sdio_func[i]->dev);
}
/*
* First add the card to the driver model...
*/
mmc_release_host(host);
err = mmc_add_card(host->card);
if (err)
goto remove_added;
/*
* ...then the SDIO functions.
*/
for (i = 0;i < funcs;i++) {
err = sdio_add_func(host->card->sdio_func[i]);
if (err)
goto remove_added;
}
mmc_claim_host(host);
return 0;
remove_added:
/* Remove without lock if the device has been added. */
mmc_sdio_remove(host);
mmc_claim_host(host);
remove:
/* And with lock if it hasn‘t been added. */
mmc_release_host(host);
if (host->card)
mmc_sdio_remove(host);
mmc_claim_host(host);
err:
mmc_detach_bus(host);
pr_err("%s: error %d whilst initialising SDIO card\n",
mmc_hostname(host), err);
return err;
}
比较难以理解的是func，这个东东其实是一个实体设备的封装，可以认为其是一个设备。
/*
* Allocate and initialise a new SDIO function structure.
*/
struct sdio_func *sdio_alloc_func(struct mmc_card *card)
{
struct sdio_func *func;
func = kzalloc(sizeof(struct sdio_func), GFP_KERNEL);
if (!func)
return ERR_PTR(-ENOMEM);
func->card = card;
device_initialize(&func->dev);
func->dev.parent = &card->dev;//card设备为sdio设备的父设备。
func->dev.bus = &sdio_bus_type;
func->dev.release = sdio_release_func;
return func;
}
上面的code一目了然，其就是具体设备实体的封装，其bus类型为sdio_bus. sdio_init_func仅仅是初始化一个设备，而并没有register。在sdio_add_func实现设备的register，同理就是card实体，在mmc_add_card之前并没有注册，在mmc_add_card函数中才实现设备的注册。
到此设备注册也就完成了，其实sdio总线在形式上类似于usb bus，为什么呢？编写过usb驱动的童鞋们应该知道，编写usb驱动仅仅是编写驱动的加载，并没有具体加载设备实体，导致很多童鞋的困惑，为什么没有设备的加载，其实在usb设备插入时，会动态的创建一个usb设备实体，在usb设备实体创建完成后，根据不同设备id调用相匹配的驱动。而SDIO设备设备也是一样的。上面的code比较混乱，总是让人看不出具体的设备的加载。其实在上面的code中，其中包括了mmc host的驱动。