Linux设备模型之mmc，sd子系统<三>

文章由LinuxBoy分享于2019-03-28 01:03:32热评（354）

Linux设备模型之mmc，sd子系统<三>

####看一下重要的卡扫描函数，mmc_rescan,卡就指着他
####活着呢，

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Linux设备模型之mmc，sd子系统<一>

Linux设备模型之mmc，sd子系统<二>

/driver/mmc/core/core.c

void mmc_rescan(struct work_struct *work)

{

static const unsigned freqs[] = { 400000, 300000, 200000, 100000 }; //扫描试验的频率段

struct mmc_host *host =

container_of(work, struct mmc_host, detect.work);

int i;

if (host->rescan_disable) //disable 直接返回
return;

mmc_bus_get(host); //增加bus引用计数

/*
* if there is a _removable_ card registered, check whether it is
* still present
*/
if (host->bus_ops && host->bus_ops->detect && !host->bus_dead
&& !(host->caps & MMC_CAP_NONREMOVABLE))
host->bus_ops->detect(host); //存在热插拔卡，不包括emmc，调用探测函数

/*
* Let mmc_bus_put() free the bus/bus_ops if we've found that
* the card is no longer present.
*/
mmc_bus_put(host); //减少引用技术，就释放
mmc_bus_get(host); //重新增加引用计数

/* if there still is a card present, stop here */
if (host->bus_ops != NULL) {
mmc_bus_put(host); //如果卡仍然存在，减少引用计数，不必探测了
goto out;
}

/*
* Only we can add a new handler, so it's safe to
* release the lock here.
*/
mmc_bus_put(host); //减少引用计数

if (host->ops->get_cd && host->ops->get_cd(host) == 0) //有卡，退出
goto out;

mmc_claim_host(host);                   //用于检测host是否被占用，占用则退出，否则标记成占用
for (i = 0; i < ARRAY_SIZE(freqs); i++) {
  if (!mmc_rescan_try_freq(host, max(freqs[i], host->f_min)))   //利用不同的频率探测卡
   break;
  if (freqs[i] <= host->f_min)
   break;
}
mmc_release_host(host);

out:

if (host->caps & MMC_CAP_NEEDS_POLL) //轮询标志，设置了就会轮询

mmc_schedule_delayed_work(&host->detect, HZ);

}

#####

/**

* mmc_claim_host - exclusively claim a host

* @host: mmc host to claim

* Claim a host for a set of operations.

static inline void mmc_claim_host(struct mmc_host *host)

{

__mmc_claim_host(host, NULL);

}

#####
/**
* __mmc_claim_host - exclusively claim a host
* @host: mmc host to claim
* @abort: whether or not the operation should be aborted
*
* Claim a host for a set of operations. If @abort is non null and
* dereference a non-zero value then this will return prematurely with
* that non-zero value without acquiring the lock. Returns zero
* with the lock held otherwise.
*/
int __mmc_claim_host(struct mmc_host *host, atomic_t *abort)
{
DECLARE_WAITQUEUE(wait, current); //定义一个等待队列
unsigned long flags;
int stop;

might_sleep();                                            //调度点

add_wait_queue(&host->wq, &wait);
spin_lock_irqsave(&host->lock, flags);
while (1) {
  set_current_state(TASK_UNINTERRUPTIBLE);
  stop = abort ? atomic_read(abort) : 0;
  if (stop || !host->claimed || host->claimer == current)
   break;
  spin_unlock_irqrestore(&host->lock, flags);
  schedule();
  spin_lock_irqsave(&host->lock, flags);
}                                                                                        //只有claim为空的时候还会跳出循环，否则就一直等待释放
set_current_state(TASK_RUNNING);
if (!stop) {
  host->claimed = 1;
  host->claimer = current;
  host->claim_cnt += 1;
} else
  wake_up(&host->wq);
spin_unlock_irqrestore(&host->lock, flags);
remove_wait_queue(&host->wq, &wait);
if (!stop)
  mmc_host_enable(host);   //使能该host
return stop;
}

#####
mmc_host_enable函数可以做一些底电流工作

#####

/**
* mmc_host_enable - enable a host.
* @host: mmc host to enable
*
* Hosts that support power saving can use the 'enable' and 'disable'
* methods to exit and enter power saving states. For more information
* see comments for struct mmc_host_ops.
*/
int mmc_host_enable(struct mmc_host *host)
{
if (!(host->caps & MMC_CAP_DISABLE))
return 0;

if (host->en_dis_recurs)
return 0;

if (host->nesting_cnt++)
return 0;

cancel_delayed_work_sync(&host->disable);

if (host->enabled)
return 0;

if (host->ops->enable) {
int err;

  host->en_dis_recurs = 1;
  err = host->ops->enable(host);
  host->en_dis_recurs = 0;

  if (err) {
   pr_debug("%s: enable error %d\n",
     mmc_hostname(host), err);
   return err;
  }
}
host->enabled = 1;
return 0;
}

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