mini2440 sd卡加载过程详解

最近在研究wifi模组， 是sdio接口的， 而手头刚好有一块mini2440，了解了一下sdio加载的过程， 发现和sd卡加载的过程是类似的。 

这里用mini2440的内核源码， 来剖析一下sd卡的加载过程：

首先， mini2440内核加载的时候， 就会指定一部分设备初始化列表：

//---------------------------- arch/arm/mach-s3c2440/mach-mini2440.c ----------------------------// /* devices we initialise */ static struct platform_device *mini2440_devices[] __initdata = {&s3c_device_usb,&s3c_device_rtc,&s3c_device_lcd,&s3c_device_wdt,&s3c_device_i2c0,&s3c_device_iis,&mini2440_device_eth,&s3c24xx_uda134x,&s3c_device_nand,&s3c_device_sdi, // sd设备&s3c_device_usbgadget, }; /* MMC/SD */ static struct s3c24xx_mci_pdata mini2440_mmc_cfg = {.gpio_detect = S3C2410_GPG(8), // 插入检测引脚.gpio_wprotect = S3C2410_GPH(8), // 写保护引脚.set_power = NULL,.ocr_avail = MMC_VDD_32_33|MMC_VDD_33_34, // 有效电压范围是3.2~3.3V, 3.3~3.4V };static void __init mini2440_machine_init(void) {s3c_device_sdi.dev.platform_data = &mini2440_mmc_cfg; platform_add_devices(mini2440_devices, ARRAY_SIZE(mini2440_devices)); }来看看s3c_device_sdi的定义：

//---------------------------- arch/arm/plat-s3c24xx/devs.c ----------------------------// /* SDI */ static struct resource s3c_sdi_resource[] = {[0] = {.start = S3C24XX_PA_SDI,.end = S3C24XX_PA_SDI + S3C24XX_SZ_SDI - 1,.flags = IORESOURCE_MEM,},[1] = {.start = IRQ_SDI,.end = IRQ_SDI,.flags = IORESOURCE_IRQ,}};struct platform_device s3c_device_sdi = {.name = "s3c2410-sdi",.id = -1,.num_resources = ARRAY_SIZE(s3c_sdi_resource),.resource = s3c_sdi_resource, };有些人会奇怪， 我们这里不是在讲解2440吗， 为什么这里是s3c2410-sdi, 别急， 往下看：

//---------------------------- arch/arm/mach-s3c2440/mach-mini2440.c ----------------------------// static void __init mini2440_machine_init(void) {s3c_device_sdi.dev.platform_data = &mini2440_mmc_cfg; platform_add_devices(mini2440_devices, ARRAY_SIZE(mini2440_devices)); }//---------------------------- arch/arm/plat-s3c24xx/s3c244x.c ----------------------------// void __init s3c244x_map_io(void) {iotable_init(s3c244x_iodesc, ARRAY_SIZE(s3c244x_iodesc));/* rename any peripherals used differing from the s3c2410 */s3c_device_sdi.name = "s3c2440-sdi"; // 重命名为s3c2440-sdis3c_device_i2c0.name = "s3c2440-i2c";s3c_device_nand.name = "s3c2440-nand";s3c_device_usbgadget.name = "s3c2440-usbgadget"; }理解了吧?  

接下来讲sd驱动的加载：

//---------------------------- drivers/mmc/host/s3cmci.c ----------------------------// static struct platform_device_id s3cmci_driver_ids[] = {{.name = "s3c2410-sdi",.driver_data = 0,}, {.name = "s3c2412-sdi",.driver_data = 1,}, {.name = "s3c2440-sdi",.driver_data = 1, // 下面会用到！！！},{ } };static struct platform_driver s3cmci_driver = {.driver = {.name = "s3c-sdi",.owner = THIS_MODULE,.pm = s3cmci_pm_ops,},.id_table = s3cmci_driver_ids,.probe = s3cmci_probe,.remove = __devexit_p(s3cmci_remove),.shutdown = s3cmci_shutdown, };static int __init s3cmci_init(void) {return platform_driver_register(&s3cmci_driver); }module_init(s3cmci_init); 驱动和设备匹配上的话，就会调用驱动的probe函数：

static int __devinit s3cmci_probe(struct platform_device *pdev) {struct s3cmci_host *host;struct mmc_host *mmc;is2440 = platform_get_device_id(pdev)->driver_data; // 是否是2440, 这里就用到上面提到的driver_data,mmc = mmc_alloc_host(sizeof(struct s3cmci_host), &pdev->dev); // 分配mmc_host结构体for (i = S3C2410_GPE(5); i <= S3C2410_GPE(10); i++) { // SDCLK SDCMD DATA0～DATA3ret = gpio_request(i, dev_name(&pdev->dev)); // 申请gpio资源if (ret) {dev_err(&pdev->dev, "failed to get gpio %d\n", i);for (i--; i >= S3C2410_GPE(5); i--)gpio_free(i);goto probe_free_host;}}host = mmc_priv(mmc); // 获取private域host->mmc = mmc;host->pdev = pdev;host->is2440 = is2440;host->pdata = pdev->dev.platform_data; // 即上面提到的mini2440_mmc_cfgif (!host->pdata) {pdev->dev.platform_data = &s3cmci_def_pdata;host->pdata = &s3cmci_def_pdata;}if (is2440) {host->sdiimsk = S3C2440_SDIIMSK;host->sdidata = S3C2440_SDIDATA;host->clk_div = 1;} else {host->sdiimsk = S3C2410_SDIIMSK;host->sdidata = S3C2410_SDIDATA;host->clk_div = 2;}// 申请内存host->mem = platform_get_resource(pdev, IORESOURCE_MEM, 0); // 这里会读取IORESOURCE_MEM域host->mem = request_mem_region(host->mem->start,resource_size(host->mem), pdev->name);host->base = ioremap(host->mem->start, resource_size(host->mem));host->irq = platform_get_irq(pdev, 0); // 这里会读取IORESOURCE_IRQ域, 返回start地址if (host->irq == 0) {dev_err(&pdev->dev, "failed to get interrupt resouce.\n");ret = -EINVAL;goto probe_iounmap;}// 申请中断，该中断为读写SD卡数据时所产生的中断if (request_irq(host->irq, s3cmci_irq, 0, DRIVER_NAME, host)) {dev_err(&pdev->dev, "failed to request mci interrupt.\n");ret = -ENOENT;goto probe_iounmap;}// 禁止上面所申请的中断disable_irq(host->irq); host->irq_state = false;if (!host->pdata->no_detect) { // 如果SD控制器具有检测SD卡插拔状态的功能ret = gpio_request(host->pdata->gpio_detect, "s3cmci detect"); // 申请插入检测iohost->irq_cd = s3c2410_gpio_getirq(host->pdata->gpio_detect);if (host->irq_cd >= 0) {if (request_irq(host->irq_cd, s3cmci_irq_cd, // 注册插入检测中断处理函数, 申请中断，当有SD卡插入或拔出时，则进入该中断IRQF_TRIGGER_RISING |IRQF_TRIGGER_FALLING,DRIVER_NAME, host)) {dev_err(&pdev->dev,"can't get card detect irq.\n");ret = -ENOENT;goto probe_free_gpio_cd;}} else {dev_warn(&pdev->dev,"host detect has no irq available\n");gpio_direction_input(host->pdata->gpio_detect);}}if (!host->pdata->no_wprotect) { // 如果SD控制器具有写保护的功能ret = gpio_request(host->pdata->gpio_wprotect, "s3cmci wp"); // 申请写保护ioif (ret) {dev_err(&pdev->dev, "failed to get writeprotect\n");goto probe_free_irq_cd;}gpio_direction_input(host->pdata->gpio_wprotect);}if (s3cmci_host_usedma(host)) { // 如果使用dma...}host->clk = clk_get(&pdev->dev, "sdi");ret = clk_enable(host->clk); // 使能clkhost->clk_rate = clk_get_rate(host->clk); // 通过时钟信号源获取时钟频率mmc->ops = &s3cmci_ops;mmc->ocr_avail = MMC_VDD_32_33 | MMC_VDD_33_34; // 默认是支持3.2~3.3V和3.3~3.4V #ifdef CONFIG_MMC_S3C_HW_SDIO_IRQmmc->caps = MMC_CAP_4_BIT_DATA | MMC_CAP_SDIO_IRQ; #elsemmc->caps = MMC_CAP_4_BIT_DATA; #endifmmc->f_min = host->clk_rate / (host->clk_div * 256);mmc->f_max = host->clk_rate / host->clk_div;if (host->pdata->ocr_avail)mmc->ocr_avail = host->pdata->ocr_avail; // 如果用户自定义了ocr_avail,即支持的工作电压，则使用自定义mmc->max_blk_count = 4095; // 一次请求的最大block数mmc->max_blk_size = 4095; // block的最大值mmc->max_req_size = 4095 * 512; // 一次请求的最大字节数mmc->max_seg_size = mmc->max_req_size; // 最大块大小mmc->max_phys_segs = 128;mmc->max_hw_segs = 128;ret = s3cmci_cpufreq_register(host);ret = mmc_add_host(mmc); // 将mmc_host添加进系统s3cmci_debugfs_attach(host); platform_set_drvdata(pdev, mmc); }其中： static struct mmc_host_ops s3cmci_ops = {.request = s3cmci_request, // 实现命令和数据的传输.set_ios = s3cmci_set_ios, // 设置硬件的IO, 包括工作电压等 .get_ro = s3cmci_get_ro, // 读取写保护的状态.get_cd = s3cmci_card_present, // 获取卡是否还存在的状态.enable_sdio_irq = s3cmci_enable_sdio_irq, };从对s3cmci_probe函数的分析可以看出，该函数除了对s3cmci_host和mmc_host这两个结构体赋值外，
最重要的工作就是调用了mmc_alloc_host函数和mmc_add_host函数。前者分配一个mmc_host，后者添加一个mmc_host。
下面我们就来介绍这两个函数，这两个函数都在drivers/mmc/core/host.c文件内。
//---------------------------- drivers/mmc/core/host.c ----------------------------// struct mmc_host *mmc_alloc_host(int extra, struct device *dev) {host = kzalloc(sizeof(struct mmc_host) + extra, GFP_KERNEL);err = idr_get_new(&mmc_host_idr, host, &host->index); // 分配新的idr入口dev_set_name(&host->class_dev, "mmc%d", host->index); // 设置设备的名字host->parent = dev;host->class_dev.parent = dev;host->class_dev.class = &mmc_host_class;// 初始化设备结构体device_initialize(&host->class_dev);spin_lock_init(&host->lock);init_waitqueue_head(&host->wq); // 初始化等待队列，工作队列INIT_DELAYED_WORK(&host->detect, mmc_rescan); // 添加到等待队列INIT_DELAYED_WORK_DEFERRABLE(&host->disable, mmc_host_deeper_disable);/** 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_seg_size = PAGE_CACHE_SIZE;host->max_req_size = PAGE_CACHE_SIZE;host->max_blk_size = 512;host->max_blk_count = PAGE_CACHE_SIZE / 512;return host; }int mmc_add_host(struct mmc_host *host) {...err = device_add(&host->class_dev);mmc_start_host(host);... }在mmc_add_host函数内，调用mmc_start_host函数来启动SD：

//---------------------------- drivers/mmc/core/core.c ----------------------------// void mmc_start_host(struct mmc_host *host) {mmc_power_off(host);mmc_detect_change(host, 0); }static void mmc_power_off(struct mmc_host *host) {host->ios.clock = 0;host->ios.vdd = 0;if (!mmc_host_is_spi(host)) {host->ios.bus_mode = MMC_BUSMODE_OPENDRAIN;host->ios.chip_select = MMC_CS_DONTCARE;}host->ios.power_mode = MMC_POWER_OFF;host->ios.bus_width = MMC_BUS_WIDTH_1; // 单线模式host->ios.timing = MMC_TIMING_LEGACY;mmc_set_ios(host); // 设置工作电压和模式 }void mmc_detect_change(struct mmc_host *host, unsigned long delay) {mmc_schedule_delayed_work(&host->detect, delay); }static int mmc_schedule_delayed_work(struct delayed_work *work, unsigned long delay) {return queue_delayed_work(workqueue, work, delay); }在mmc_start_host函数内调用mmc_detect_change函数来检测是否有SD卡已经插入。mmc_detect_change函数又调用mmc_schedule_delayed_work函数，mmc_schedule_delayed_work函数又调用了queue_delayed_work函数。
这样经过一段延时后，会执行在mmc_alloc_host函数中定义的工作队列（INIT_DELAYED_WORK(&host->detect,mmc_rescan);）所指向的mmc_rescan函数。
为什么要延时，这和按键去抖延时相类似。

下面我们来介绍mmc_rescan函数，它用来具体执行扫描并检测是否有SD卡插入的：

void mmc_rescan(struct work_struct *work) {struct mmc_host *host = container_of(work, struct mmc_host, detect.work);/* if there is a card registered, check whether it is still present */if ((host->bus_ops != NULL) && host->bus_ops->detect && !host->bus_dead)host->bus_ops->detect(host); // 如果已经注册过该卡，则检测卡是否还在/* if there still is a card present, stop here */// host->bus_ops != NULL，说明这次mmc_rescan不是在上电初始化时调用的// 所以不需要执行if后面的内容，要直接执行mmc_schedule_delayed_work函数if (host->bus_ops != NULL) { // 如果卡还在， 则直接退出mmc_bus_put(host);goto out;}/* detect a newly inserted card */ // 检测新插入的卡/** 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) // 如果有插入检测引脚， 但是检测该引脚的状态是无卡，则退出goto out;// 判断当前mmc控制器是否被占用mmc_claim_host(host);mmc_power_up(host); // 上电mmc_go_idle(host); // 发送命令CMD0，使其处于IDLE状态mmc_send_if_cond(host, host->ocr_avail); // 发送SD_SEND_IF_COND命令，以支持SD2.0卡// 依次探测SDIO、SD、MMC/** First we search for SDIO...*/err = mmc_send_io_op_cond(host, 0, &ocr);if (!err) {if (mmc_attach_sdio(host, ocr))mmc_power_off(host);goto out;}/** ...then normal SD...*/err = mmc_send_app_op_cond(host, 0, &ocr);if (!err) {if (mmc_attach_sd(host, ocr))mmc_power_off(host);goto out;}/** ...and finally MMC.*/err = mmc_send_op_cond(host, 0, &ocr);if (!err) {if (mmc_attach_mmc(host, ocr))mmc_power_off(host);goto out;}mmc_release_host(host);mmc_power_off(host); }我们以SDIO卡为例，因此会调用mmc_attach_sdio函数，它实现了SDIO卡的初始化：
//---------------------------- drivers/mmc/core/sd.c ----------------------------// /** Starting point for SD card init.*/ int mmc_attach_sd(struct mmc_host *host) {int err;u32 ocr, rocr;err = mmc_send_app_op_cond(host, 0, &ocr);if (err)return err;mmc_sd_attach_bus_ops(host);if (host->ocr_avail_sd)host->ocr_avail = host->ocr_avail_sd;/** We need to get OCR a different way for SPI.*/if (mmc_host_is_spi(host)) {mmc_go_idle(host);err = mmc_spi_read_ocr(host, 0, &ocr);if (err)goto err;}// 设置电压，最终调用的是s3cmci_set_ios函数rocr = mmc_select_voltage(host, ocr);/** Can we support the voltage(s) of the card(s)?*/if (!rocr) {err = -EINVAL;goto err;}/* 检测和初始化卡* Detect and init the card.* 在mmc_sd_init_card函数内，会通过发送一系列命令来启动SD卡，并得到寄存器CID，CSD，SCR，RCA等的数据。*/err = mmc_sd_init_card(host, rocr, NULL);if (err)goto err;mmc_release_host(host);/* 添加卡, 它通过调用device_add函数把mmc_card设备添加进系统中，并通知mmc块设备驱动。* First add the card to the driver model...*/err = mmc_add_card(host->card);mmc_claim_host(host);if (err)goto remove_card;return 0;remove_card:mmc_release_host(host);mmc_remove_card(host->card);host->card = NULL;mmc_claim_host(host); err:mmc_detach_bus(host);pr_err("%s: error %d whilst initialising SD card\n",mmc_hostname(host), err);return err; }static void mmc_sd_attach_bus_ops(struct mmc_host *host) {const struct mmc_bus_ops *bus_ops;if (!mmc_card_is_removable(host))bus_ops = &mmc_sd_ops_unsafe;elsebus_ops = &mmc_sd_ops;mmc_attach_bus(host, bus_ops); }static const struct mmc_bus_ops mmc_sd_ops = {.remove = mmc_sd_remove, // 拔出sd卡的操作.detect = mmc_sd_detect, // 探测sd卡的操作.suspend = NULL,.resume = NULL,.power_restore = mmc_sd_power_restore,.alive = mmc_sd_alive,.shutdown = mmc_sd_suspend, }; 至此，mmc子系统的启动及检测SD卡设备就完成了。这个SD卡的检测是在上电之前就已插入插槽的，那么如果上电以后再把SD卡插入插槽中，系统又是如何检测的呢？
在前面介绍s3cmci_probe函数的时候，申请了两个中断，一个用于数据传输，另一个就是用于检测SD卡的。也就是当SD卡插入时，会引起相关引脚的电平变化，从而触发该中断，进入中断处理函数s3cmci_irq_cd：
//---------------------------- drivers\mmc\host/s3cmci.c ----------------------------// static irqreturn_t s3cmci_irq_cd(int irq, void *dev_id) {struct s3cmci_host *host = (struct s3cmci_host *)dev_id;dbg(host, dbg_irq, "card detect\n");mmc_detect_change(host->mmc, msecs_to_jiffies(500));return IRQ_HANDLED; } mmc_detect_change函数前面介绍过，它是用来检测是否存在SD卡。它的第二个参数表示延时的时间。在这里一定是要有延时的。
调用mmc_detect_change函数后所执行的内容与前面介绍的一样，这里就不再重复了。
 
无论是上电之前还是上电之后，SD卡的插入检测我们在上面都详细介绍完了，那么SD卡的拔出是如何检测的呢？当然一定是带电状态下才能检测SD卡的拔出的。
是回到mmc_rescan函数中：
void mmc_rescan(struct work_struct *work) {...struct mmc_host *host = container_of(work, struct mmc_host, detect.work);/* if there is a card registered, check whether it is still present */if ((host->bus_ops != NULL) && host->bus_ops->detect && !host->bus_dead)host->bus_ops->detect(host); // 如果已经注册过该卡，则检测卡是否还在... } 上面的语句就是用来检测SD卡的拔出的。我们在前面也已经介绍过了，在mmc_attach_bus函数内，把mmc_sd_ops赋给了host->bus_ops，
所以host->bus_ops->detect(host);实际回调的是mmc_sd_detect函数。
这里可能会有一个疑问：mmc_attach_bus函数是在mmc_rescan函数之后被调用的，那么就是说在mmc_rescan函数内，mmc_host->bus_ops还没有被赋值，
所以就不会回调mmc_sd_detect函数了。
我们要注意一点的是，mmc_rescan函数是在上电初始化过程中会被执行一次，因此在初始化的过程中完成了mmc_host->bus_ops的赋值。
而检测SD卡的拔出一定是在完成初始化以后，这时mmc_host->bus_ops已经被赋值，所以执行mmc_rescan函数中的
host->bus_ops->detect(host);语句不会出现任何问题。

我们来看看回调函数mmc_sd_detect，它定义在drivers/mmc/core/sd.c文件内：

/** Card detection callback from host.*/ static void mmc_sd_detect(struct mmc_host *host) {int err = 0; #ifdef CONFIG_MMC_PARANOID_SD_INITint retries = 5; #endifBUG_ON(!host);BUG_ON(!host->card);mmc_get_card(host->card);/** Just check if our card has been removed.*/ #ifdef CONFIG_MMC_PARANOID_SD_INITwhile(retries) {err = mmc_send_status(host->card, NULL);if (err) {retries--;udelay(5);continue;}break;}if (!retries) {printk(KERN_ERR "%s(%s): Unable to re-detect card (%d)\n",__func__, mmc_hostname(host), err);} #elseerr = _mmc_detect_card_removed(host); #endifmmc_put_card(host->card);if (err) {mmc_sd_remove(host);mmc_claim_host(host);mmc_detach_bus(host);mmc_power_off(host);mmc_release_host(host);} }为什么要用给SD卡发送状态信息来判断SD卡是否存活（即是否被拔出）？因为当把SD卡拔出时，当然是得不到任何SD卡的信息，所以会出错。
我们再回到mmc_sdio_detect函数内，如果SD卡已拔出，mmc_select_card函数返回非零值，则执行下面的if里的内容。

下面我们来验证一下SD驱动。把SD卡插入开发板的插槽中，上电启动开发板，如果系统能够打印出类似下面的信息，则说明开发板能够识别出SD卡：

s3c-sdi s3c2440-sdi: running at 0kHz (requested: 0kHz). s3c-sdi s3c2440-sdi: running at 398kHz (requested: 400kHz). s3c-sdi s3c2440-sdi: running at 398kHz (requested: 400kHz). s3c-sdi s3c2440-sdi: running at 398kHz (requested: 400kHz). s3c-sdi s3c2440-sdi: running at 398kHz (requested: 400kHz). s3c-sdi s3c2440-sdi: running at 398kHz (requested: 400kHz). s3c-sdi s3c2440-sdi: running at 398kHz (requested: 400kHz). s3c-sdi s3c2440-sdi: running at 398kHz (requested: 400kHz). s3c-sdi s3c2440-sdi: running at 16875kHz (requested: 25000kHz). s3c-sdi s3c2440-sdi: running at 16875kHz (requested: 25000kHz). mmc0: new SDHC card at address aaaa mmcblk0: mmc0:aaaa SS08G 7.40 GiB mmcblk0: p1

如果先把开发板上电，然后再把SD卡插入插槽中，则系统也会自动打印出上面的信息。如果我们在带电的情况下把SD卡拔出，则系统会自动打印出类似下面的信息：

mmc0: card aaaa removed s3c-sdis3c2440-sdi: powered down.

总结

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