最近在解EMMC的一個bug，發現Linux EMMC有點小複雜，先整理個文檔出來吧
用的是TI 平臺，僅分析MMC，不分析SD和SDIO
mmc_init
2769 static int __init mmc_init(void)
2770 {
2774
2775 workqueue = alloc_ordered_workqueue("kmmcd", 0);
2776 if (!workqueue)
2777 return -ENOMEM;
2778
2779 ret = mmc_register_bus();
2780 if (ret)
2781 goto destroy_workqueue;
2782
2783 ret = mmc_register_host_class();
2784 if (ret)
2785 goto unregister_bus;;
2793
2802 }
2775分配一個workqueue，這個workqueue是專門用來處理card detect的，EMMC因爲是unremovable的，所以不需要關注它
2779 註冊mmc_bus_type，實現如下：
int mmc_register_bus(void)
{
return bus_register(&mmc_bus_type);
}
mmc_init調用時間比較早，會在host驅動初始化之前執行完。
subsys_initcall(mmc_init);host驅動初始化
kernel/drivers/mmc/host/omap_hsmmc.c
host驅動位置是kernel/drivers/mmc/host/，一般來說都是platform_driver，以omap hsmmc host驅動爲例
<strong>.probe = omap_hsmmc_probe,</strong>
.remove = omap_hsmmc_remove,
.driver = {
.name = DRIVER_NAME,
.owner = THIS_MODULE,
.pm = &omap_hsmmc_dev_pm_ops,
.of_match_table = of_match_ptr(omap_mmc_of_match),
},
};
module_platform_driver(omap_hsmmc_driver);只需要關注omap_hsmmc_probe即可，當系統匹配到platform_device時，會調用omap_hsmmc_probe，好長的一個函數
2627 base = devm_ioremap_resource(&pdev->dev, res);
2628 if (IS_ERR(base))
2629 return PTR_ERR(base);
2630
2631 ret = omap_hsmmc_gpio_init(pdata);
2632 if (ret)
2633 goto err;
omap_hsmmc_gpio_init是card detect和write protect gpio的初始化，Ignore it!!!
2635 mmc = mmc_alloc_host(sizeof(struct omap_hsmmc_host), &pdev->dev);
2636 if (!mmc) {
2637 ret = -ENOMEM;
2638 goto err_alloc;
2639 }
...............
2661 mmc->ops = &omap_hsmmc_ops;
2410 static const struct mmc_host_ops omap_hsmmc_ops = {
2411 .enable = omap_hsmmc_enable_fclk,
2412 .disable = omap_hsmmc_disable_fclk,
2413 .post_req = omap_hsmmc_post_req,
2414 .pre_req = omap_hsmmc_pre_req,
2415 .request = omap_hsmmc_request,
2416 .set_ios = omap_hsmmc_set_ios,
2417 .get_cd = omap_hsmmc_get_cd,
2418 .get_ro = omap_hsmmc_get_ro,
2419 .init_card = omap_hsmmc_init_card,
2420 .start_signal_voltage_switch = omap_start_signal_voltage_switch,
2421 .card_busy = omap_hsmmc_card_busy,
2422 .execute_tuning = omap_execute_tuning,
2423 /* NYET -- enable_sdio_irq */
2424 };
2663 mmc->f_min = OMAP_MMC_MIN_CLOCK;
2675 if (pdata->max_freq > 0) {
2676 mmc->f_max = pdata->max_freq;
2677 ret = clk_set_rate(host->fclk, pdata->max_freq);
2678 if (ret) {
2679 dev_err(dev, "failed to set clock to %d\n",
2680 pdata->max_freq);
2681 goto err1;
2682 }
2683 } else {
2684 mmc->f_max = OMAP_MMC_MAX_CLOCK;
2685 }
2724 mmc->max_segs = 1024;
2725
2726 mmc->max_blk_size = 512; /* Block Length at max can be 1024 */
2727 mmc->max_blk_count = 0xFFFF; /* No. of Blocks is 16 bits */
2728 mmc->max_req_size = mmc->max_blk_size * mmc->max_blk_count;
2729 mmc->max_seg_size = mmc->max_req_size;
mmc作爲快設備，最主要的操作就是數據sectors讀寫，max_segs定義了block設備的request所支持的最大segment
max_blk_count 一個request中所包含的最大block數
其實多少都不重要，反正就是和request相關的一些上限。
2731 mmc->caps |= MMC_CAP_MMC_HIGHSPEED | MMC_CAP_SD_HIGHSPEED |
2732 MMC_CAP_WAIT_WHILE_BUSY | MMC_CAP_ERASE;
2733
2734 mmc->caps |= mmc_slot(host).caps;
2735 if (mmc->caps & MMC_CAP_8_BIT_DATA)
2736 mmc->caps |= MMC_CAP_4_BIT_DATA;
2737 if (mmc_slot(host).nonremovable)
2738 mmc->caps |= MMC_CAP_NONREMOVABLE;
2741
2742 if (of_property_read_bool(np, "sd-uhs-sdr12"))
2743 mmc->caps |= MMC_CAP_UHS_SDR12;
2744 if (of_property_read_bool(np, "sd-uhs-sdr25"))
2745 mmc->caps |= MMC_CAP_UHS_SDR25;
2746 if (of_property_read_bool(np, "sd-uhs-sdr50"))
2747 mmc->caps |= MMC_CAP_UHS_SDR50;
2748 if (of_property_read_bool(np, "sd-uhs-sdr104"))
2749 mmc->caps |= MMC_CAP_UHS_SDR104;
2750 if (of_property_read_bool(np, "sd-uhs-ddr50"))
2751 mmc->caps |= MMC_CAP_UHS_DDR50;
2752 if (of_property_read_bool(np, "mmc-ddr-1_8v"))
2753 mmc->caps |= MMC_CAP_1_8V_DDR;
2754 if (of_property_read_bool(np, "mmc-hs200-1_8v"))
2755 mmc->caps2 |= MMC_CAP2_HS200_1_8V_SDR;
MMCCAP_MMC_HIGHSPEED, MMC_CAP_SD_HIGHSPEED MMC_CAP_WAIT_WHILE_BUSY MMC_CAP_ERASE是最基本的能力
MMC_CAP_8_BIT_DATA表示數據總線是多少，EMMC 數據線支持8線，4線和1線。
2742 ~ 2755 通過of系統定義的一些特定能力，當前MMC_CAP_1_8V_DDR，MMC_CAP2_HS200_1_8V_SDR都很常見了。DDR是Double Date Rate的縮寫，SDR是Single Data Rate的縮寫
自行腦補百度資料DDR SDRAM， EMMC的DDR SDR與之類似。
DDR=Double Data Rate雙倍速率同步動態隨機存儲器。嚴格的說DDR應該叫DDR SDRAM，人們習慣稱爲DDR，其中，SDRAM 是Synchronous Dynamic Random Access Memory的縮寫，
即同步動態隨機存取存儲器。而DDR SDRAM是Double Data Rate SDRAM的縮寫，是雙倍速率同步動態隨機存儲器的意思。DDR內存是在SDRAM內存基礎上發展而來的，仍然沿用SDRAM生產體系，
一個時鐘週期內進行兩次讀/寫操作，即在時鐘的上升沿和下降沿分別執行一次讀/寫操作。
注意對於EMMC CMD線來說，是沒有DDR SDR說法的，CMD和response只在clock的上升沿傳輸，參見EMMC spec5.0 section 6.15.1
2773 omap_hsmmc_conf_bus_power(host);2775 if (!pdev->dev.of_node) {
2776 res = platform_get_resource_byname(pdev, IORESOURCE_DMA, "tx");
2777 if (!res) {
2778 dev_err(mmc_dev(host->mmc), "cannot get DMA TX channel\n");
2779 ret = -ENXIO;
2780 goto err_irq;
2781 }
2782 tx_req = res->start;
2783
2784 res = platform_get_resource_byname(pdev, IORESOURCE_DMA, "rx");
2785 if (!res) {
2786 dev_err(mmc_dev(host->mmc), "cannot get DMA RX channel\n");
2787 ret = -ENXIO;
2788 goto err_irq;
2789 }
2790 rx_req = res->start;
2791 }
2792
2793 dma_cap_zero(mask);
2794 dma_cap_set(DMA_SLAVE, mask);
2795
2796 host->rx_chan =
2797 dma_request_slave_channel_compat(mask, omap_dma_filter_fn,
2798 &rx_req, &pdev->dev, "rx");
2799
2800 if (!host->rx_chan) {
2801 dev_err(mmc_dev(host->mmc), "unable to obtain RX DMA engine channel %u\n", rx_req);
2802 ret = -ENXIO;
2803 goto err_irq;
2804 }
2805
2806 host->tx_chan =
2807 dma_request_slave_channel_compat(mask, omap_dma_filter_fn,
2808 &tx_req, &pdev->dev, "tx");
DMA相關的代碼，內核中EMMC驅動必然要使用DMA方式讀寫數據，
dma_request_slave_channel_compat分配一個DMA channel
2816 /* Request IRQ for MMC operations */
2817 ret = devm_request_irq(&pdev->dev, host->irq, omap_hsmmc_irq, 0,
2818 mmc_hostname(mmc), host);
2819 if (ret) {
2820 dev_err(mmc_dev(host->mmc), "Unable to grab HSMMC IRQ\n");
2821 goto err_irq;
2822 }
2864 mmc_add_host(mmc);
drivers/mmc/core/host.c
538 int mmc_add_host(struct mmc_host *host)
539 {
557 mmc_start_host(host);
562 }
mmc_start_host->_mmc_detect_change -> mmc_rescan ->mmc_rescan_try_freq，對於REMOVALBE設備，rescan可以進行多次，而對於mmc這樣的NON-REMOVABLE設備，只需掃描一次即可。
host會使用不同的頻率發送命令到device，因此這個函數也是嘗試設置f_init的過程
2362 static int mmc_rescan_try_freq(struct mmc_host *host, unsigned freq)
2363 {
2364 host->f_init = freq;
2365
2371 mmc_power_up(host, host->ocr_avail);
2372
2389 /* Order's important: probe SDIO, then SD, then MMC */
2390 if (!mmc_attach_sdio(host))
2391 return 0;
2392 if (!mmc_attach_sd(host))
2393 return 0;
2394 if (!mmc_attach_mmc(host)) {
2395 printk(KERN_ERR "%s: end, host->index=%d\n", __func__, host->index);
2396 return 0;
2397 }
2401 }
mmc_power_up Power_up流程，可參見MMC spec5.0 A6.1，首先設置總線操作電壓，然後設置clock
mmc_attach_mmc: mmc 卡初始化函數
1785 int mmc_attach_mmc(struct mmc_host *host)
1786 {
1792
1794 /* Set correct bus mode for MMC before attempting attach */
1795 if (!mmc_host_is_spi(host))
1796 mmc_set_bus_mode(host, MMC_BUSMODE_OPENDRAIN);
1797
1798 err = mmc_send_op_cond(host, 0, &ocr);
1799 if (err)
1800 return err;
1804
1805 mmc_attach_bus_ops(host);
1806 if (host->ocr_avail_mmc)
1807 host->ocr_avail = host->ocr_avail_mmc;
1808
1817
1818 rocr = mmc_select_voltage(host, ocr);
1819
1827
1828 /*
1829 * Detect and init the card.
1830 */
1831 err = mmc_init_card(host, rocr, NULL);
1832 if (err)
1833 goto err;
1834
1835 mmc_release_host(host);
1836 err = mmc_add_card(host->card);
1837 mmc_claim_host(host);
1838 if (err)
1839 goto remove_card;
1840
1842 return 0;
1856 }
mmc_send_op_cond等待device完成power up過程
mmc_select_voltage檢查前面獲得的ocr，判斷ocr中標稱的電壓，返回的ocr爲處理過的ocr
mmc_init_card 會讀取cid csd ext_csd，並根據這些寄存器的值做一些初始化操作。
133 int mmc_send_op_cond(struct mmc_host *host, u32 ocr, u32 *rocr)
134 {
135 struct mmc_command cmd = {0};
136 int i, err = 0;
139
140 cmd.opcode = MMC_SEND_OP_COND;
141 cmd.arg = mmc_host_is_spi(host) ? 0 : ocr;
142 cmd.flags = MMC_RSP_SPI_R1 | MMC_RSP_R3 | MMC_CMD_BCR;
143
144 for (i = 100; i; i--) {
145 err = mmc_wait_for_cmd(host, &cmd, 0);
146 if (err)
147 break;
148
149 /* if we're just probing, do a single pass */
150 if (ocr == 0)
151 break;
152
153 /* otherwise wait until reset completes */
154 if (mmc_host_is_spi(host)) {
155 if (!(cmd.resp[0] & R1_SPI_IDLE))
156 break;
157 } else {
158 if (cmd.resp[0] & MMC_CARD_BUSY)
159 break;
160 }
161
162 err = -ETIMEDOUT;
163
164 mmc_delay(10);
165 }
166
167 if (rocr && !mmc_host_is_spi(host))
168 *rocr = cmd.resp[0];
169
170 return err;
171 }
158 如果發現ocr的最高位爲1，表示mmc device已經完成power up，否則循環發送CMD1，直到mmc device 完成power up
969 static int mmc_init_card(struct mmc_host *host, u32 ocr,
970 struct mmc_card *oldcard)
971 {
995
996 /* The extra bit indicates that we support high capacity */
997 err = mmc_send_op_cond(host, ocr | (1 << 30), &rocr);
998 if (err)
999 goto err;
1000
1010 /*
1011 * Fetch CID from card.
1012 */
1013 if (mmc_host_is_spi(host))
1014 err = mmc_send_cid(host, cid);
1015 else
1016 err = mmc_all_send_cid(host, cid);
1017 if (err)
1018 goto err;
1016 mmc_all_send_cid 發送CMD10，並等待device 返回R2。CMD10請求設備發送CID給host
1047 /*
1048 * For native busses: set card RCA and quit open drain mode.
1049 */
1050 if (!mmc_host_is_spi(host)) {
1051 err = mmc_set_relative_addr(card);
1052 if (err)
1053 goto free_card;
1054
1055 mmc_set_bus_mode(host, MMC_BUSMODE_PUSHPULL);
1056 }
1058 if (!oldcard) {
1059 /*
1060 * Fetch CSD from card.
1061 */
1062 err = mmc_send_csd(card, card->raw_csd);
1063 if (err)
1064 goto free_card;
1065
1066 err = mmc_decode_csd(card);
1067 if (err)
1068 goto free_card;
1069 err = mmc_decode_cid(card);
1070 if (err)
1071 goto free_card;
1072 }
1077 if (!mmc_host_is_spi(host)) {
1078 err = mmc_select_card(card);
1079 if (err)
1080 goto free_card;
1081 }
1083 if (!oldcard) {
1084 /*
1085 * Fetch and process extended CSD.
1086 */
1087
1088 err = mmc_get_ext_csd(card, &ext_csd);
1089 if (err)
1090 goto free_card;
1091 err = mmc_read_ext_csd(card, ext_csd);
1092 if (err)
1093 goto free_card;
1094
1095 /* If doing byte addressing, check if required to do sector
1096 * addressing. Handle the case of <2GB cards needing sector
1097 * addressing. See section 8.1 JEDEC Standard JED84-A441;
1098 * ocr register has bit 30 set for sector addressing.
1099 */
1100 if (!(mmc_card_blockaddr(card)) && (rocr & (1<<30)))
1101 mmc_card_set_blockaddr(card);
1102
1103 /* Erase size depends on CSD and Extended CSD */
1104 mmc_set_erase_size(card);
1105 }
1088 獲取ext_csd，ext_csd的獲取，需要發送MMC_SEND_EXT_CSD，並從data線上獲取device發送回ext_csd
1091 解析獲取的ext_csd
1174 if (card->ext_csd.hs_max_dtr != 0) {
1175 err = 0;
1176 if (card->ext_csd.hs_max_dtr > 52000000 &&
1177 host->caps2 & MMC_CAP2_HS200)
1178 err = mmc_select_hs200(card);
1179 else if (host->caps & MMC_CAP_MMC_HIGHSPEED)
1180 err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
1181 EXT_CSD_HS_TIMING, 1,
1182 card->ext_csd.generic_cmd6_time);
1183
1184 if (err && err != -EBADMSG)
1185 goto free_card;
1186
1187 if (err) {
1188 pr_warning("%s: switch to highspeed failed\n",
1189 mmc_hostname(card->host));
1190 err = 0;
1191 } else {
1192 if (card->ext_csd.hs_max_dtr > 52000000 &&
1193 host->caps2 & MMC_CAP2_HS200) {
1194 mmc_card_set_hs200(card);
1195 mmc_set_timing(card->host,
1196 MMC_TIMING_MMC_HS200);
1198 } else {
1199 mmc_card_set_highspeed(card);
1200 mmc_set_timing(card->host, MMC_TIMING_MMC_HS);
1202 }
1203 }
1204 }
那麼理論上總線應該能跑到HS200，此時就設置ext_csd.hs_max_dtr爲MMC_HS200_MAX_DTR
mmc_select_hs200設置device的timing爲HS200
mmc_set_timing則設置host的timing 爲HS200
1211 if (mmc_card_highspeed(card) || mmc_card_hs200(card)) {
1212 if (max_dtr > card->ext_csd.hs_max_dtr)
1213 max_dtr = card->ext_csd.hs_max_dtr;
1214 if (mmc_card_highspeed(card) && (max_dtr > 52000000))
1215 max_dtr = 52000000;
1216 } else if (max_dtr > card->csd.max_dtr) {
1217 max_dtr = card->csd.max_dtr;
1218 }
1219
1220 printk(KERN_ERR "%s: mmc_set_clock() max_dtr=%d\n", __func__, max_dtr);
1221 mmc_set_clock(host, max_dtr);
設置host的最大clock
1267 ext_csd_bits = (bus_width == MMC_BUS_WIDTH_8) ?
1268 EXT_CSD_BUS_WIDTH_8 : EXT_CSD_BUS_WIDTH_4;
1269 err = mmc_select_powerclass(card, ext_csd_bits);但是低耗電帶來的副作用就是性能的損失，所以linux emmc core 驅動都是性能優先。
mmc_add_card
309 int mmc_add_card(struct mmc_card *card)
310 {
351
352 if (mmc_card_uhs(card) &&
353 (card->sd_bus_speed < ARRAY_SIZE(uhs_speeds)))
354 uhs_bus_speed_mode = uhs_speeds[card->sd_bus_speed];
355
356 if (mmc_host_is_spi(card->host)) {
357 pr_info("%s: new %s%s%s card on SPI\n",
358 mmc_hostname(card->host),
359 mmc_card_highspeed(card) ? "high speed " : "",
360 mmc_card_ddr_mode(card) ? "DDR " : "",
361 type);
362 } else {
363 pr_info("%s: new %s%s%s%s%s card at address %04x\n",
364 mmc_hostname(card->host),
365 mmc_card_uhs(card) ? "ultra high speed " :
366 (mmc_card_highspeed(card) ? "high speed " : ""),
367 (mmc_card_hs200(card) ? "HS200 " : ""),
368 mmc_card_ddr_mode(card) ? "DDR " : "",
369 uhs_bus_speed_mode, type, card->rca);
370 }
379 ret = device_add(&card->dev);
352~370會輸出mmc card的一些信息，比如high speed, HS200；DDR等
379會調用設備模型，增加設備，因爲card屬於mmc_bus，會調用mmc_bus_probe
110 static int mmc_bus_probe(struct device *dev)
111 {
112 int ret;
113 struct mmc_driver *drv = to_mmc_driver(dev->driver);
114 struct mmc_card *card = mmc_dev_to_card(dev);
115
117 ret = drv->probe(card);
118
120 return ret;
121 }
這樣理解，每個mmc設備也是一個block設備，因此這個mmc設備，也要對應一個mmc block驅動。mmc block驅動需要調用驅動本身的probe函數，探測這個block設備
2429 static int mmc_blk_probe(struct mmc_card *card)
2430 {
2431 struct mmc_blk_data *md, *part_md;
2432 char cap_str[10];
2439
2440 md = mmc_blk_alloc(card);
2441 if (IS_ERR(md))
2442 return PTR_ERR(md);
2443
2444 string_get_size((u64)get_capacity(md->disk) << 9, STRING_UNITS_2,
2445 cap_str, sizeof(cap_str));
2446 pr_info("%s: %s %s %s %s\n",
2447 md->disk->disk_name, mmc_card_id(card), mmc_card_name(card),
2448 cap_str, md->read_only ? "(ro)" : "");
2449
2450 if (mmc_blk_alloc_parts(card, md))
2451 goto out;
2452
2453 mmc_set_drvdata(card, md);
2454 mmc_fixup_device(card, blk_fixups);
2455
2456 if (mmc_add_disk(md))
2457 goto out;
2458
2459 list_for_each_entry(part_md, &md->part, part) {
2460 if (mmc_add_disk(part_md))
2461 goto out;
2462 }
2467 /*
2468 * Don't enable runtime PM for SD-combo cards here. Leave that
2469 * decision to be taken during the SDIO init sequence instead.
2470 */
2471 if (card->type != MMC_TYPE_SD_COMBO) {
2472 pm_runtime_set_active(&card->dev);
2473 pm_runtime_enable(&card->dev);
2474 }
2475
2476 return 0;
2477
2478 out:
2479 mmc_blk_remove_parts(card, md);
2480 mmc_blk_remove_req(md);
2481 return 0;
2482 }
2440 每一個mmc_card都對應一個mmc_blk_data，mmc_blk_data管理快設備相關的數據。
2450 mmc設備內部可能預先分配了boot partitions，以及最多四個general purpose partitions，需要爲這些內置分區分配part。注意這些分區在系統中是以通用磁盤的形式存在的，並不是傳統意義上的分區。
2456 mmc_add_disk增加mmc 設備到系統中，mmc_add_disk會調用add_disk向系統內增加通用硬盤，這個函數比較複雜，會單獨開一個帖子分析add_disk的流程。
mmc_add_disk結束後，mmc設備的分區信息也已經添加到系統中。
mmc_blk_data主要實現函數是mmc_blk_alloc_req
2074 static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
2075 struct device *parent,
2076 sector_t size,
2077 bool default_ro,
2078 const char *subname,
2079 int area_type)
2080 {
2116 md->disk = alloc_disk(perdev_minors);
2117 if (md->disk == NULL) {
2118 ret = -ENOMEM;
2119 goto err_kfree;
2120 }
2126 ret = mmc_init_queue(&md->queue, card, &md->lock, subname);
2127 if (ret)
2128 goto err_putdisk;
2116 alloc_disk分配一個gendisk結構，在linux內核中gendisk用來表示一個磁盤或者分區
2126 初始化該塊設備的queue，從這裏我們可以看出不管mmc_blk_data對應是磁盤還是分區，都會爲它分配queue。這是合理的，比如我們可以通過/dev/mmcblk0訪問設備，也可以通過/dev/mmcblk0p1訪問設備。
