emmc检测及初始化

本文将基于emmc驱动来描述系统是如何检测到emmc设备，并进行初始化操作的。

一、中断处理函数mmci_cd_irq

在前面关于mmc驱动的系列文章emmc/sd host层解析中有关于mmci的的分析，在文章中有分析过一个名为mmci_probe的函数，该函数比较长，这里就不完全贴出来了，只贴出跟emmc检测相关的代码，如下：

/* * A gpio pin that will detect cards when inserted and removed * will most likely want to trigger on the edges if it is * 0 when ejected and 1 when inserted (or mutatis mutandis * for the inverted case) so we request triggers on both * edges. */ret = request_any_context_irq(gpio_to_irq(plat->gpio_cd),mmci_cd_irq,IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,DRIVER_NAME " (cd)", host);

注释说：一个gpio的pin脚会检测卡的插入和移除。

这段代码是注册一个中断号对应的中断函数，而这个中断就是对应卡插入或者移除的。

下面来看一下中断函数的实现（mmci.c）：

static irqreturn_t mmci_cd_irq(int irq, void *dev_id){struct mmci_host *host = dev_id;mmc_detect_change(host->mmc, msecs_to_jiffies(500));return IRQ_HANDLED;}

里面调用了mmc_detect_change(core/core.c)函数来检测拔插变化，实现如下：

/** *mmc_detect_change - process change of state on a MMC socket *@host: host which changed state. *@delay: optional delay to wait before detection (jiffies) * *MMC drivers should call this when they detect a card has been *inserted or removed. The MMC layer will confirm that any *present card is still functional, and initialize any newly *inserted. */void mmc_detect_change(struct mmc_host *host, unsigned long delay){_mmc_detect_change(host, delay, true);}

再看_mmc_detect_change(core.c)：

static void _mmc_detect_change(struct mmc_host *host, unsigned long delay,bool cd_irq){#ifdef CONFIG_MMC_DEBUGunsigned long flags;spin_lock_irqsave(&host->lock, flags);WARN_ON(host->removed);spin_unlock_irqrestore(&host->lock, flags);#endif/* * If the device is configured as wakeup, we prevent a new sleep for * 5 s to give provision for user space to consume the event. */if (cd_irq && !(host->caps & MMC_CAP_NEEDS_POLL) &&device_can_wakeup(mmc_dev(host)))pm_wakeup_event(mmc_dev(host), 5000);host->detect_change = 1;mmc_schedule_delayed_work(&host->detect, delay);}

这里，重点看下最后一行代码。

二、mmc_schedule_delayed_work(&host->detect, delay)

mmc_schedule_delayed_work(&host->detect, delay);

这里延时调度了一个工作队列，再展开看一下：

/* * Internal function. Schedule delayed work in the MMC work queue. */static int mmc_schedule_delayed_work(struct delayed_work *work,     unsigned long delay){return queue_delayed_work(workqueue, work, delay);}

从传递的参数类型我们可以知道，host->detect是个delayed_work类型的变量，那么它是在什么时候被赋值的呢？

这个我们得从mmci_probe函数说起，该函数中有这样一段代码：

mmc = mmc_alloc_host(sizeof(struct mmci_host), &dev->dev);

而mmc_alloc_host函数中有如下代码：

INIT_DELAYED_WORK(&host->detect, mmc_rescan);

这里将mmc_rescan处理函数赋值给了detect下的工作队列处理函数指针，也就是说如果以后调度detect队列时，就会使用mmc_rescan函数去处理。

也就是说mmc_schedule_delayed_work实际调用了mmc_rescan函数。
三、mmc_rescan

void mmc_rescan(struct work_struct *work){struct mmc_host *host =container_of(work, struct mmc_host, detect.work);int i;if (host->rescan_disable)return;/* If there is a non-removable card registered, only scan once */if ((host->caps & MMC_CAP_NONREMOVABLE) && host->rescan_entered)return;host->rescan_entered = 1;mmc_bus_get(host);/* * 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);host->detect_change = 0;/* * Let mmc_bus_put() free the bus/bus_ops if we've found that * the card is no longer present. */mmc_bus_put(host);mmc_bus_get(host);/* if there still is a card present, stop here */if (host->bus_ops != NULL) {mmc_bus_put(host);goto out;}/* * Only we can add a new handler, so it's safe to * release the lock here. */mmc_bus_put(host);if (host->ops->get_cd && host->ops->get_cd(host) == 0) {mmc_claim_host(host);mmc_power_off(host);mmc_release_host(host);goto out;}mmc_claim_host(host);for (i = 0; i < ARRAY_SIZE(freqs); i++) {if (!mmc_rescan_try_freq(host, max(freqs[i], host->f_min)))break;if (freqs[i] <= host->f_min)break;}mmc_release_host(host); out:if (host->caps & MMC_CAP_NEEDS_POLL)mmc_schedule_delayed_work(&host->detect, HZ);}

第46行之前，自己看注释；主要是将host的bus_ops置空；

第46行，调用了host的ops的get_cd函数指针对应的函数，在这里就不分析ops指向了谁，直接上函数指针对应的函数（mmci.c）：

static int mmci_get_cd(struct mmc_host *mmc){struct mmci_host *host = mmc_priv(mmc);struct mmci_platform_data *plat = host->plat;unsigned int status;if (host->gpio_cd == -ENOSYS) {if (!plat->status)return 1; /* Assume always present */status = plat->status(mmc_dev(host->mmc));} elsestatus = !!gpio_get_value_cansleep(host->gpio_cd)^ plat->cd_invert;/* * Use positive logic throughout - status is zero for no card, * non-zero for card inserted. */return status;}

从最后的注释可以知道，如果函数返回0表示没有卡插入，如果返回非0表示有卡插入。

回到mmc_rescan的第46行，如果此时没有卡则进入if语句中，关闭电源并退出，否则执行下面的流程。

第54--59行:这里出现了一个名为freqs的数组，先看下它的定义：

static const unsigned freqs[] = { 400000, 300000, 200000, 100000 };

这个应该是一个时钟频率数组。

看第55行的mmc_rescan_try_freq：

static int mmc_rescan_try_freq(struct mmc_host *host, unsigned freq){host->f_init = freq;#ifdef CONFIG_MMC_DEBUGpr_info("%s: %s: trying to init card at %u Hz\n",mmc_hostname(host), __func__, host->f_init);#endifmmc_power_up(host, host->ocr_avail);/* * Some eMMCs (with VCCQ always on) may not be reset after power up, so * do a hardware reset if possible. */mmc_hw_reset_for_init(host);/* * sdio_reset sends CMD52 to reset card.  Since we do not know * if the card is being re-initialized, just send it.  CMD52 * should be ignored by SD/eMMC cards. */sdio_reset(host);mmc_go_idle(host);mmc_send_if_cond(host, host->ocr_avail);/* Order's important: probe SDIO, then SD, then MMC */if (!mmc_attach_sdio(host))return 0;if (!mmc_attach_sd(host))return 0;if (!mmc_attach_mmc(host))return 0;mmc_power_off(host);return -EIO;}

第9行：给设备上电；

第15行：给emmc设备硬件重置；

第22行：如果是sdio重置；

第23行：发送CMD0命令，设置idle状态；

第25行：发送SD_SEND_IF_COND（SD卡的CMD8）命令，判断当前工作电压是否符合要求。emmc不会响应。

第28行：内部通过发送SD_IO_SEND_OP_COND（CMD5）检测是否为sdio设备，是调用mmc_sdio_init_card进行初始化；

第30行：内部通过发送SD_APP_OP_COND（CMD41）检测是否为sd设备，是调用mmc_sd_init_card进行初始化；

第32行：内部通过发送MMC_SEND_OP_COND（CMD1）检测是否为emmc设备，是则调用mmc_init_card函数进行初始化，关于mmc_init_card函数在linux关机时emmc驱动处理流程文章的第十节有详细讲解，有兴趣的自行阅读。

如果上面的三种检测操作有一个操作成功就直接返回0。如果不 成功则执行第35行的下电操作，并返回非0.

到此我们的emmc初始化完毕了。