通過MMC驅動的實際案例說明MMC驅動編寫的一般步驟
下文將通過核心原始碼(Linux Kernel 5.2)對MMC驅動子系統進行簡述,並通過MMC驅動的實際案例說明MMC驅動編寫的一般步驟,同時分析驅動模型下完成驅動、裝置繫結的過程。如對Linux裝置驅動模型不熟悉,可以參考另一篇博文:
2. MMC 匯流排的註冊
MMC匯流排的註冊和platform匯流排的註冊方法相同,均是呼叫bus_register()函式。函式的呼叫入口位於mmc/core/core.c,通過mmc_init()實現,此處主要關注MMC的部分。
/* drivers/mmc/core/core.c */ subsys_initcall(mmc_init); static int __init mmc_init(void) { int ret; ret = mmc_register_bus(); if (ret) return ret; ret = mmc_register_host_class(); if (ret) goto unregister_bus; ret = sdio_register_bus(); if (ret) goto unregister_host_class; return 0; unregister_host_class: mmc_unregister_host_class(); unregister_bus: mmc_unregister_bus(); return ret; }
/*********************************************************** * mmc bus 匯流排註冊 ***********************************************************/ static struct bus_type mmc_bus_type = { .name = "mmc", .dev_groups = mmc_dev_groups, .match = mmc_bus_match, .uevent = mmc_bus_uevent, .probe = mmc_bus_probe, .remove = mmc_bus_remove, .shutdown = mmc_bus_shutdown, .pm = &mmc_bus_pm_ops, }; int mmc_register_bus(void) { return bus_register(&mmc_bus_type); }
/*********************************************************** * mmc_host class 類註冊 ***********************************************************/ static struct class mmc_host_class = { .name = "mmc_host", .dev_release = mmc_host_classdev_release, }; int mmc_register_host_class(void) { return class_register(&mmc_host_class); }
主要包括兩個方面:
- 利用bus_register()註冊mmc_bus。對應sysfs下的/sys/bus/mmc/目錄。
- 利用class_register()註冊mmc_host_class。對應sysfs下的/sys/class/mmc_host目錄。
3. MMC 驅動(mmc_driver)的註冊
drivers/mmc/core/block.c中將mmc_driver註冊到mmc_bus對應的匯流排系統裡。主要步驟包括:
- 通過register_blkdev()向核心註冊塊裝置。
- 呼叫driver_register()將mmc_driver註冊到mmc_bus匯流排系統。和其他驅動註冊方式一致。
mmc_driver註冊完成之後,會在sysfs中建立目錄/sys/bus/mmc/drivers/mmcblk。
/* drivers/mmc/core/block.c */ module_init(mmc_blk_init); static struct mmc_driver mmc_driver = { .drv = { .name = "mmcblk", .pm = &mmc_blk_pm_ops, }, .probe = mmc_blk_probe, .remove = mmc_blk_remove, .shutdown = mmc_blk_shutdown, }; static int __init mmc_blk_init(void) { int res; ... ... res = register_blkdev(MMC_BLOCK_MAJOR, "mmc"); ... res = mmc_register_driver(&mmc_driver); ... return 0; ... ... } /** * mmc_register_driver - register a media driver * @drv: MMC media driver */ int mmc_register_driver(struct mmc_driver *drv) { drv->drv.bus = &mmc_bus_type; return driver_register(&drv->drv); }
4. MMC 裝置的註冊
前文已經簡單描述過,MMC裝置主要包括主裝置host和從裝置card兩部分,而主裝置host將被封裝在platform_device中註冊到驅動模型中。
為了更加清晰地描述此部分的註冊過程,下文將以一個驅動為例分析(此驅動原始碼只包含關鍵步驟程式碼,只為描述MMC驅動的編寫基本框架,demo mmc driver)。
module_init(xxx_mmc_init); #define DRIVER_NAME "xxx_mmc" /* platform driver definition */ static struct platform_driver xxx_mmc_driver = { .probe = xxx_mmc_probe, .remove = xxx_mmc_remove, .driver = { .name = DRIVER_NAME, }, }; static struct platform_device *pdev; static __init int xxx_mmc_init(void) { int err = 0; /* * Register platform driver into driver model */ // 將xxx_mmc_driver註冊到驅動模型中 err = platform_driver_register(&xxx_mmc_driver); /* * Allocate platform device and register into driver model * This will call driver->probe() */ // 動態分配platform_device,並將其註冊到驅動模型中 // 此過程會回撥driver->probe()函式 pdev = platform_device_alloc(DRIVER_NAME, 0); err = platform_device_add(pdev); return err; }
從程式碼中看到,驅動入口函式中將註冊platform_driver和platform_device,name均定義為xxx_mmc。根據驅動模型,最終會回撥xxx_mmc_driver中的probe()函式:xxx_mmc_probe()。
4.1 xxx_mmc_probe(pdev)
// 自定義的mmc_host_ops,用於host做實際操作時回撥 static const struct mmc_host_ops xxx_mmc_ops = { .request = xxx_mmc_request, .set_ios = xxx_mmc_set_ios, }; /* platform driver probe function */ static int xxx_mmc_probe(struct platform_device *pdev) { struct mmc_host *mmc; struct xxx_mmc_host *host = NULL; int ret = 0; /* Step 1: Allocate host structure */ // 第1步:動態分配mmc_host結構 mmc = mmc_alloc_host(sizeof(struct xxx_mmc_host), &pdev->dev); if (mmc == NULL) { pr_err("alloc host failed\n"); ret = -ENOMEM; goto err_alloc_host; } // pointer initialization host = mmc_priv(mmc); host->mmc = mmc; host->id = pdev->id; /* Step 2: Initialize struct mmc_host */ // 第2步:初始化mmc_host的結構成員 mmc->ops = &xxx_mmc_ops; mmc->f_min = 400000; mmc->f_max = 52000000; mmc->ocr_avail = MMC_VDD_32_33; mmc->caps = MMC_CAP_8_BIT_DATA | MMC_CAP_NONREMOVABLE | MMC_CAP_MMC_HIGHSPEED; mmc->caps2 = MMC_CAP2_BOOTPART_NOACC | MMC_CAP_PANIC_WRITE; mmc->max_segs = 1; mmc->max_blk_size = 512; mmc->max_req_size = 65536; // Maximum number of bytes in one req mmc->max_blk_count = mmc->max_req_size/mmc->max_blk_size; // Maximum number of blocks in one req mmc->max_seg_size = mmc->max_req_size; // Segment size in one req, in bytes host->dev = &pdev->dev; platform_set_drvdata(pdev, host); // pdev->dev->driver_data = host /* Step 3: Register the host with driver model */ // 第3步:將mmc_host註冊到驅動模型中 mmc_add_host(mmc); return 0; err_alloc_host: return ret; }
xxx_mmc_probe(pdev)主要工作如下:
- 呼叫mmc_alloc_host()分配一個structmmc_host結構。
- 對structmmc_host結構體成員初始化。
- 呼叫mmc_add_host()
將structmmc_host
加入到驅動模型中。
4.2 mmc_alloc_host(sizeof(struct xxx_mmc_host), &pdev->dev)
/* drivers/mmc/core/host.c */ static DEFINE_IDA(mmc_host_ida); /* mmc_alloc_host - initialise the per-host structure. */ struct mmc_host *mmc_alloc_host(int extra, struct device *dev) { int err; struct mmc_host *host; host = kzalloc(sizeof(struct mmc_host) + extra, GFP_KERNEL); if (!host) return NULL; /* scanning will be enabled when we're ready */ host->rescan_disable = 1; // Allocate an unused ID err = ida_simple_get(&mmc_host_ida, 0, 0, GFP_KERNEL); if (err < 0) { kfree(host); return NULL; } host->index = err; dev_set_name(&host->class_dev, "mmc%d", host->index); // 此處可以稍微注意一下,host->class_dev的類class設定為mmc_host_class // 並且host->class_dev的parent指向了pdev->dev (platform_device) // 這些許的差異會改變device_add後在sysfs中表現出來的層次結構 host->parent = dev; // host->parent = &pdev->dev host->class_dev.parent = dev; // host->class_dev.parent = &pdev->dev host->class_dev.class = &mmc_host_class; // Initialize host->class_dev device_initialize(&host->class_dev); device_enable_async_suspend(&host->class_dev); if (mmc_gpio_alloc(host)) { put_device(&host->class_dev); return NULL; } // 初始化自旋鎖 spin_lock_init(&host->lock); // 初始化等待佇列頭 init_waitqueue_head(&host->wq); // 初始化延遲的工作佇列`host->detect`和`host->sdio_irq_work` INIT_DELAYED_WORK(&host->detect, mmc_rescan); INIT_DELAYED_WORK(&host->sdio_irq_work, sdio_irq_work); timer_setup(&host->retune_timer, mmc_retune_timer, 0); host->max_segs = 1; host->max_seg_size = PAGE_SIZE; host->max_req_size = PAGE_SIZE; host->max_blk_size = 512; host->max_blk_count = PAGE_SIZE / 512; host->fixed_drv_type = -EINVAL; host->ios.power_delay_ms = 10; return host; }
主要工作如下:
- 動態分配記憶體給structmmc_host結構體,並對結構體成員初始化。
- 呼叫device_initialize()對host->class_dev進行初始化,包括kobject、mutex等。
- 初始化自旋鎖、等待佇列 (waitqueue)和延遲的工作佇列 (Delayed Work),其中,用處理函式mmc_rescan()來初始化延遲的工作佇列host->detect,後文會再次提到。
- 初始化定時器host->retune_timer,處理函式為mmc_retune_timer()。
4.3 mmc_add_host(mmc)
在上述對host進行初始化後,呼叫mmc_add_host()將host註冊到驅動模型中。
/* drivers/mmc/core/host.c */ /* mmc_add_host - initialise host hardware */ int mmc_add_host(struct mmc_host *host) { int err; WARN_ON((host->caps & MMC_CAP_SDIO_IRQ) && !host->ops->enable_sdio_irq); err = device_add(&host->class_dev); if (err) return err; led_trigger_register_simple(dev_name(&host->class_dev), &host->led); #ifdef CONFIG_DEBUG_FS mmc_add_host_debugfs(host); #endif mmc_start_host(host); mmc_register_pm_notifier(host); return 0; }
主要的工作包括兩個部分:
- device_add()將host->class_dev加入到sysfs中device層次結構中。
- 呼叫mmc_start_host()啟動主裝置,也即MMC裝置開始正常工作。
在介紹mmc_start_host()之前,先簡單介紹下此處將host->class_dev加入到驅動模型後sysfs中表現出來的層次結構。 4.2一節中介紹mmc_alloc_host()時注意到host->class_dev的class被設定為mmc_host_class,parent指向pdev->dev。device_add()-->get_device_parent()/device_add_class_symlinks()呼叫過程中將在platform_device的目錄下多建立一個名稱和classname相同的子資料夾,同時在class類目錄下也會有指向實際裝置的目錄項。sysfs此時的結構如下:
/sys/devices/platform/xxx_mmc.0/mmc_host/mmc0$ ll total 0 ... ... root root 0 Sep 17 11:21 ./ ... ... root root 0 Sep 17 11:21 ../ ... ... root root 0 Sep 17 11:23 device -> ../../../xxx_mmc.0/ ... ... root root 0 Sep 17 11:23 power/ ... ... root root 0 Sep 17 11:23 subsystem -> ../../../../../class/mmc_host/ ... ... root root 4096 Sep 17 11:23 uevent /sys/class/mmc_host$ ll /sys/class/mmc_host total 0 ... ... root root 0 Sep 17 11:21 ./ ... ... root root 0 Sep 17 11:09 ../ ... ... root root 0 Sep 17 11:26 mmc0 -> ../../devices/platform/xxx_mmc.0/mmc_host/mmc0/
此時mmc_host結構體成員初始化狀態簡要列舉如下(詳細可以按照驅動模型中device
註冊步驟推導):
4.4 mmc_add_host(mmc)
/* drivers/mmc/core/core.c */ void mmc_start_host(struct mmc_host *host) { host->f_init = max(freqs[0], host->f_min); host->rescan_disable = 0; host->ios.power_mode = MMC_POWER_UNDEFINED; if (!(host->caps2 & MMC_CAP2_NO_PRESCAN_POWERUP)) { mmc_claim_host(host); mmc_power_up(host, host->ocr_avail); mmc_release_host(host); } mmc_gpiod_request_cd_irq(host); _mmc_detect_change(host, 0, false); }
- host->rescan_disable =0使能主裝置的重新檢測。
- 未使能MMC_CAP2_NO_PRESCAN_POWERU
P
時,將完成claim_host()、power_up()、release_host()等一系列工作。 - mmc_gpiod_request_cd_irq()用於為host申請中斷號(和GPIO口對應),並繫結中斷服務函式。
- _mmc_detect_change(host,0,false)用於檢測MMC槽位上的變動。
mmc_claim_host(host)函式用於申請獲得host(主控制器)的使用權,程序將進入休眠等待狀態,直至可以獲得主控制器的使用權。該函式結合mmc_release_host(host),利用等待佇列實現,原理細節可以參考:Linux等待佇列(Wait Queue)。
4.5 _mmc_detect_change(host, 0, false)
static void _mmc_detect_change(struct mmc_host *host, unsigned long delay, bool cd_irq) { 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); } static int mmc_schedule_delayed_work(struct delayed_work *work, unsigned long delay) { return queue_delayed_work(system_freezable_wq, work, delay); }
_mmc_detect_change()函式用來檢測MMC狀態的改變,具體是通過排程工作佇列實現,如4.2一節介紹,mmc_rescan()作為處理函式被繫結在延遲工作佇列host->detect上。因此,此處實際上是啟動mmc_rescan()的執行過程。
4.6 mmc_rescan(&host->detect)
void mmc_rescan(struct work_struct *work) { // 通過host->detect指標得到mmc_host結構體指標 struct mmc_host *host = container_of(work, struct mmc_host, detect.work); // 如果rescan被禁止,函式提前返回 if (host->rescan_disable) return; // 對於不可移除(non-removable)的host,如果其正在做rescan工作時,函式提前返回(scan只做一次) if (!mmc_card_is_removable(host) && host->rescan_entered) return; // 基本檢查通過,進入rescan流程,標記rescan_entered host->rescan_entered = 1; ... ... // 檢查可移除(removable) host是否還存在 if (host->bus_ops && !host->bus_dead && mmc_card_is_removable(host)) host->bus_ops->detect(host); host->detect_change = 0; ... ... // 嘗試獲得host的使用權,實現原理在4.4小節中有提及 mmc_claim_host(host); ... ... // rescan流程的關鍵步驟,依次嘗試四個給定頻率,直至檢測到mmc card的存在 // static const unsigned freqs[] = { 400000, 300000, 200000, 100000 } 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); ... ... }
static int mmc_rescan_try_freq(struct mmc_host *host, unsigned freq) { host->f_init = freq; // 完成一系列初始化步驟,保證裝置在合適的執行狀態,為後面實際探測做準備 mmc_power_up(host, host->ocr_avail); mmc_hw_reset_for_init(host); ... ... mmc_go_idle(host); if (!(host->caps2 & MMC_CAP2_NO_SD)) mmc_send_if_cond(host, host->ocr_avail); /* Order's important: probe SDIO, then SD, then MMC */ // 依次探測裝置:SDIO,SD,MMC // 對於MMC裝置,嘗試呼叫mmc_attach_mmc(host) if (!(host->caps2 & MMC_CAP2_NO_SDIO)) if (!mmc_attach_sdio(host)) return 0; if (!(host->caps2 & MMC_CAP2_NO_SD)) if (!mmc_attach_sd(host)) return 0; if (!(host->caps2 & MMC_CAP2_NO_MMC)) if (!mmc_attach_mmc(host)) return 0; mmc_power_off(host); return -EIO; }
mmc_rescan(&host->detect)會呼叫mmc_rescan_try_freq(host, max(freqs[i], host->f_min)),進一步呼叫重要的mmc_attach_mmc(host)函式,將MMC裝置加入到驅動模型中。
4.7 mmc_attach_mmc(&host)
// mmc_bus相關的一系列operations函式 static const struct mmc_bus_ops mmc_ops = { .remove = mmc_remove, .detect = mmc_detect, .suspend = mmc_suspend, .resume = mmc_resume, .runtime_suspend = mmc_runtime_suspend, .runtime_resume = mmc_runtime_resume, .alive = mmc_alive, .shutdown = mmc_shutdown, .hw_reset = _mmc_hw_reset, }; // MMC card初始化的入口函式 int mmc_attach_mmc(struct mmc_host *host) { int err; u32 ocr, rocr; // 首先檢查host的使用權是否已經獲得 WARN_ON(!host->claimed); /* Set correct bus mode for MMC before attempting attach */ if (!mmc_host_is_spi(host)) mmc_set_bus_mode(host, MMC_BUSMODE_OPENDRAIN); // OCR register獲得,可參考MMC裝置操作規範 err = mmc_send_op_cond(host, 0, &ocr); // 將host結構成員bus_ops設定為mmc_ops mmc_attach_bus(host, &mmc_ops); ... ... // 為host選擇合適的工作電壓 rocr = mmc_select_voltage(host, ocr); ... ... // 關鍵步驟1:開始初始化MMC card的流程 err = mmc_init_card(host, rocr, NULL); // MMC card初始化後釋放host的使用權,起初在mmc_rescan()函式中獲得 mmc_release_host(host); // 關鍵步驟2:將MMC card註冊進裝置驅動模型中 err = mmc_add_card(host->card); mmc_claim_host(host); return 0; ... ... }
mmc_attach_mmc(&host)作為MMC card檢測和初始化的關鍵函式,執行的步驟可概括為:
- 獲取MMC基本硬體初始化資訊,例如OCR register (工作電壓相關)
- 初始化host->bus_ops成員,host->bus_ops = &mmc_ops
- mmc_init_card(host, rocr, NULL):MMC card初始化,下文詳細介紹
- mmc_add_card(host->card):將MMC card加入到裝置驅動模型中,下文將詳細介紹
4.8 mmc_init_mmc(&host, rocr, NULL)
static struct device_type mmc_type = { .groups = mmc_std_groups, }; static int mmc_init_card(struct mmc_host *host, u32 ocr, struct mmc_card *oldcard) { struct mmc_card *card; int err; u32 cid[4]; u32 rocr; WARN_ON(!host->claimed); ... ... mmc_go_idle(host); /* The extra bit indicates that we support high capacity */ err = mmc_send_op_cond(host, ocr | (1 << 30), &rocr); ... ... err = mmc_send_cid(host, cid); if (oldcard) { ... card = oldcard; } else { // 動態分配mmc_card結構 card = mmc_alloc_card(host, &mmc_type); card->ocr = ocr; card->type = MMC_TYPE_MMC; card->rca = 1; memcpy(card->raw_cid, cid, sizeof(card->raw_cid)); } ... ... ... ... }
struct mmc_card *mmc_alloc_card(struct mmc_host *host, struct device_type *type) { struct mmc_card *card; card = kzalloc(sizeof(struct mmc_card), GFP_KERNEL); if (!card) return ERR_PTR(-ENOMEM); card->host = host; device_initialize(&card->dev); card->dev.parent = mmc_classdev(host); card->dev.bus = &mmc_bus_type; card->dev.release = mmc_release_card; card->dev.type = type; return card; }
mmc_init_mmc(&host, rocr, NULL)會呼叫mmc_alloc_card(host, &mmc_type)動態分配一個structmmc_card結構,並初始化其內部的structdevice結構。此外,mmc_init_mmc()中還完成了許多初始化工作,這些工作大多是依據MMC操作規範定義的,在此不詳細介紹。
structmmc_card結構成員大致列舉如下,以方便分析。
struct mmc_card card = { .host = &mmc; .dev = { .parent = mmc_classdev(mmc) = &(mmc.class_dev); .bus = &mmc_bus_type = { .name = "mmc", .dev_groups = mmc_dev_groups, .match = mmc_bus_match, .uevent = mmc_bus_uevent, .probe = mmc_bus_probe, .remove = mmc_bus_remove, .shutdown = mmc_bus_shutdown, .pm = &mmc_bus_pm_ops, }; .release = mmc_release_card; .type = &mmc_type = { .groups = mmc_std_groups, }; } .ocr = rocr; .type = MMC_TYPE_MMC; .rca = 1; // relative card address of device };
4.9 mmc_add_card(host->card)
int mmc_add_card(struct mmc_card *card) { int ret; ... ... // #define mmc_hostname(x) (dev_name(&(x)->class_dev)) // 為card->dev設定名稱“mmc0:0001”,實際上設定了card->dev->kobj.name = “mmc0:0001” dev_set_name(&card->dev, "%s:%04x", mmc_hostname(card->host), card->rca); ... ... card->dev.of_node = mmc_of_find_child_device(card->host, 0); device_enable_async_suspend(&card->dev); // 關鍵步驟:通過device_add() 將mmc card註冊到裝置驅動模型中 ret = device_add(&card->dev); // 標記mmc card狀態為PRESENT,card->state = MMC_STATE_PRESENT mmc_card_set_present(card); return 0; }
這裡最關鍵的一步是熟悉的device_add(&card->dev)函式,它將mmc card新增到驅動模型中。注意到card.dev的parent被設定為mmc.class_dev,所以將在前述host的目錄層次下建立新的名為mmc0:0001的card子目錄,而在呼叫bus_add_device()時,在mmc bus目錄下子目錄devices建立相應的連結,連結到上述mmc0:0001的裝置目錄上。sysfs的整體目錄層次表現如下:
/sys/devices/platform/xxx_mmc.0/mmc_host/mmc0/mmc0:0001$ ll total 0 ... ... block/ ... ... ... ... driver -> ../../../../../../bus/mmc/drivers/mmcblk/ ... ... ... ... subsystem -> ../../../../../../bus/mmc/ ... ... ... ... uevent /sys/bus/mmc/devices$ ll ... ... mmc0:0001 -> ../../../devices/platform/xxx_mmc.0/mmc_host/mmc0/mmc0:0001/ /sys/bus/mmc/drivers/mmcblk$ ll ... ... mmc0:0001 -> ../../../../devices/platform/xxx_mmc.0/mmc_host/mmc0/mmc0:0001/ /sys/class/mmc_host$ ll ... ... mmc0 -> ../../devices/platform/klm_emmc.0/mmc_host/mmc0/
按照Linux驅動模型,接下來要完成的是裝置和驅動在總線上的匹配工作,最終呼叫驅動的probe()
函式。呼叫的函式依次是:
mmc_bus_probe(&card.dev) --> mmc_blk_probe(&card)
5. 塊裝置裝置驅動
Linux塊裝置驅動初始化一般包括如下幾個方面:
- 申請裝置號,並將塊裝置驅動註冊到核心。register_blkdev()
- 初始化請求佇列。blk_init_queue() / blk_alloc_queue()
- 分配gendisk結構,並進行初始化。alloc_disk()
- 新增gendisk。add_disk()
第3節MMC驅動註冊中,函式mmc_blk_init()呼叫register_blkdev(MMC_BLOCK_MAJOR,"mmc")完成了裝置號的申請,將塊設備註冊到核心中。下文將從mmc_blk_probe(card)入手分析其他幾個步驟的實現。
5.1 mmc_blk_probe(card)
struct mmc_blk_data { struct device *parent; struct gendisk *disk; struct mmc_queue queue; struct list_head part; struct list_head rpmbs; unsigned int flags; unsigned int usage; unsigned int read_only; unsigned int part_type; unsigned int reset_done; ... ... };
static int mmc_blk_probe(struct mmc_card *card) { struct mmc_blk_data *md, *part_md; char cap_str[10]; ... ... card->complete_wq = alloc_workqueue("mmc_complete", WQ_MEM_RECLAIM | WQ_HIGHPRI, 0); // 分配和初始化gendisk結構,初始化請求佇列 md = mmc_blk_alloc(card); string_get_size((u64)get_capacity(md->disk), 512, STRING_UNITS_2, cap_str, sizeof(cap_str)); if (mmc_blk_alloc_parts(card, md)) goto out; dev_set_drvdata(&card->dev, md); // 新增gendisk if (mmc_add_disk(md)) goto out; list_for_each_entry(part_md, &md->part, part) { if (mmc_add_disk(part_md)) goto out; } ... return 0; ... }
mmc_blk_probe(card)為MMC card完成所有塊裝置驅動有關的工作,主要呼叫了兩個重要的函式:
- mmc_blk_alloc(card)
mmc_add_disk(md)
5.2 mmc_blk_alloc(card)
mmc_blk_alloc(card)為MMC card初始化請求佇列,函式呼叫過程為:
mmc_blk_alloc(card) --> mmc_blk_alloc_req() --> mmc_init_queue(&md->queue, card) --> blk_mq_init_queue()
static struct mmc_blk_data *mmc_blk_alloc(struct mmc_card *card) { sector_t size; if (!mmc_card_sd(card) && mmc_card_blockaddr(card)) { size = card->ext_csd.sectors; } else { size = (typeof(sector_t))card->csd.capacity << (card->csd.read_blkbits - 9); } return mmc_blk_alloc_req(card, &card->dev, size, false, NULL, MMC_BLK_DATA_AREA_MAIN); }
static const struct block_device_operations mmc_bdops = { .open = mmc_blk_open, .release = mmc_blk_release, .getgeo = mmc_blk_getgeo, .owner = THIS_MODULE, .ioctl = mmc_blk_ioctl, #ifdef CONFIG_COMPAT .compat_ioctl = mmc_blk_compat_ioctl, #endif }; static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card, struct device *parent, sector_t size, bool default_ro, const char *subname, int area_type) { struct mmc_blk_data *md; int devidx, ret; devidx = ida_simple_get(&mmc_blk_ida, 0, max_devices, GFP_KERNEL); ... ... md = kzalloc(sizeof(struct mmc_blk_data), GFP_KERNEL); md->area_type = area_type; md->read_only = mmc_blk_readonly(card); // 分配gendisk結構 md->disk = alloc_disk(perdev_minors); INIT_LIST_HEAD(&md->part); INIT_LIST_HEAD(&md->rpmbs); md->usage = 1; // 初始化請求佇列 ret = mmc_init_queue(&md->queue, card); md->queue.blkdata = md; // 初始化gendisk結構成員 md->disk->major = MMC_BLOCK_MAJOR; md->disk->first_minor = devidx * perdev_minors; // 為MMC card定義了block_device_operations結構體 md->disk->fops = &mmc_bdops; md->disk->private_data = md; md->disk->queue = md->queue.queue; md->parent = parent; set_disk_ro(md->disk, md->read_only || default_ro); md->disk->flags = GENHD_FL_EXT_DEVT; if (area_type & (MMC_BLK_DATA_AREA_RPMB | MMC_BLK_DATA_AREA_BOOT)) md->disk->flags |= GENHD_FL_NO_PART_SCAN | GENHD_FL_SUPPRESS_PARTITION_INFO; snprintf(md->disk->disk_name, sizeof(md->disk->disk_name), "mmcblk%u%s", card->host->index, subname ? subname : ""); set_capacity(md->disk, size); ... ... return md; ... ... }
值得注意的是,mmc_blk_alloc_req()函式中為將MMC card gendisk結構體的fops賦值為mmc_bdops,即為MMC card定義了open,release,getgeo,ioctl等操作的回撥函式。
5.3 mmc_init_queue(&md->queue, card)
static const struct blk_mq_ops mmc_mq_ops = { .queue_rq = mmc_mq_queue_rq, .init_request = mmc_mq_init_request, .exit_request = mmc_mq_exit_request, .complete = mmc_blk_mq_complete, .timeout = mmc_mq_timed_out, }; int mmc_init_queue(struct mmc_queue *mq, struct mmc_card *card) { struct mmc_host *host = card->host; int ret; mq->card = card; mq->use_cqe = host->cqe_enabled; spin_lock_init(&mq->lock); memset(&mq->tag_set, 0, sizeof(mq->tag_set)); // mq->tag_set.ops設定為mmc_mq_ops mq->tag_set.ops = &mmc_mq_ops; ... ... mq->tag_set.driver_data = mq; ret = blk_mq_alloc_tag_set(&mq->tag_set); if (ret) return ret; // 初始化請求佇列 mq->queue = blk_mq_init_queue(&mq->tag_set); ... ... mq->queue->queuedata = mq; blk_queue_rq_timeout(mq->queue, 60 * HZ); mmc_setup_queue(mq, card); return 0; ... ... }
struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set) { struct request_queue *uninit_q, *q; uninit_q = blk_alloc_queue_node(GFP_KERNEL, set->numa_node); q = blk_mq_init_allocated_queue(set, uninit_q); return q; }
struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set, struct request_queue *q) { // 用set->ops (mmc_mq_ops)來初始化request_queue的mq_ops成員 q->mq_ops = set->ops; ... ... blk_queue_make_request(q, blk_mq_make_request); ... ... }
mmc_init_queue(&md->queue, card)最終呼叫blk_queue_make_request(q, blk_mq_make_request)初始化了請求佇列(製造請求函式)。
另外,也使用mmc_mq_ops初始化了request_queue的mq_ops成員,下文會提到。
至此,塊裝置驅動註冊工作基本完成。
6. 請求佇列的工作流程梳理
4.1節介紹MMX裝置初始化時提到,驅動編寫過程中特別地為host編寫了mmc_host_ops,而至目前仍未介紹到其被使用的地方,本節將從請求佇列入手,通過一個簡單的情形,分析mmc_host_ops操作函式的回撥過程。
當對mmc card發起塊裝置I/O動作時,核心會首先呼叫到之前初始化的blk_mq_make_request()函式(定義在block/blk-mq.c),在特定情況下呼叫blk_mq_try_issue_directly(),最終一步步呼叫到__blk_mq_issue_directly()。
static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio) { ... blk_mq_try_issue_directly(data.hctx, rq, &cookie); .. }
static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, struct request *rq, blk_qc_t *cookie) { ... ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false, true); if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE) blk_mq_request_bypass_insert(rq, true); else if (ret != BLK_STS_OK) blk_mq_end_request(rq, ret); ... }
static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, struct request *rq, blk_qc_t *cookie, bool bypass_insert, bool last) { ... return __blk_mq_issue_directly(hctx, rq, cookie, last); ... }
static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx, struct request *rq, blk_qc_t *cookie, bool last) { struct request_queue *q = rq->q; ... ret = q->mq_ops->queue_rq(hctx, &bd); ... return ret; }
5.3一節中提到q->mq_ops指向mmc_mq_ops,因此此處最終會回撥函式mmc_mq_ops->queue_rq(),即mmc_mq_queue_rq(),最終回撥至mmc_host_ops->request(host, mrq)。
mmc_mq_queue_rq() --> mmc_blk_mq_issue_rq() --> mmc_blk_mq_issue_rw_rq() --> mmc_start_request() --> __mmc_start_request() --> host->ops->request(host, mrq)
static blk_status_t mmc_mq_queue_rq(struct blk_mq_hw_ctx *hctx, const struct blk_mq_queue_data *bd) { ... issued = mmc_blk_mq_issue_rq(mq, req); ... }
enum mmc_issued mmc_blk_mq_issue_rq(struct mmc_queue *mq, struct request *req) { ... ret = mmc_blk_mq_issue_rw_rq(mq, req); ... }
static int mmc_blk_mq_issue_rw_rq(struct mmc_queue *mq, struct request *req) { struct mmc_queue_req *mqrq = req_to_mmc_queue_req(req); struct mmc_host *host = mq->card->host; ... ... err = mmc_start_request(host, &mqrq->brq.mrq); ... ... return err; }
int mmc_start_request(struct mmc_host *host, struct mmc_request *mrq) { int err; init_completion(&mrq->cmd_completion); mmc_retune_hold(host); ... WARN_ON(!host->claimed); err = mmc_mrq_prep(host, mrq); ... __mmc_start_request(host, mrq); return 0; }
static void __mmc_start_request(struct mmc_host *host, struct mmc_request *mrq) { int err; ... err = mmc_retune(host); ... host->ops->request(host, mrq); }
7. 總結
綜合上述分析,可以將MMC驅動子系統流程分析概括為下圖。從驅動編寫的角度,只需關注MMC card設備註冊相關程式碼,主要包含如下幾個方面:
- 將mmc host封裝進一個platform device,同時定義一platform driver,並將它們註冊到驅動模型中
- platform driver的probe()函式中呼叫mmc_alloc_host()和mmc_add_host(),將mmc card註冊到驅動模型中