Linux NAND FLASH驅動程序分析(mini2440)

 

Linux NAND FLASH驅動程序分析(mini2440)

 

一、Linux-MTD Subsystem介紹

      FLASH在嵌入式系統中是必不可少的，它是bootloader、linux內核和文件系統的最佳載體。在Linux內核中引入了MTD子系統爲NOR FLASH和NAND FLASH設備提供統一的接口，從而使得FLASH驅動的設計大爲簡化。

 

      在引入MTD後Linux系統中FLASH設備驅動可分爲四層，如圖：

 

1. 硬件驅動層

    FLASH硬件驅動層負責FLASH硬件設備的讀、寫、擦出，LINUX MTD設備的NOR FLASH驅動位於/driver/mtd/chips子目錄下，NAND FLASH驅動則位於/driver/mtd/nand子目錄下。

特定硬件層負責完成特定硬件的讀寫，例如2440的/driver/mtd/nand/s3c2410.c

通用驅動爲所有nand的通用部分，實現nand設備發現，通用讀寫等./driver/mtd/nand/nand_base.c

2. MTD原始設備層：MTD原始設備層由兩部分構成，一部分是MTD原始設備的通用代碼(mtdcore.c、mtdpart.c)，另一部分是各個   特定的FLASH的數據，例如分區。

3. MTD設備層：基於MTD原始設備，LINUX系統可以定義出MTD的塊設備（主設備號31）和字符設備（設備號90），構成設備層。MTD字符設備在mtdchar.c實現，MTD塊設備在mtdblock.c實現。

4. 設備節點：通過mknod在/dev子目錄下建立MTD字符設備節點（主設備號爲90）和塊設備節點（主設備號爲31），用戶通過訪問此設備節點即可訪問MTD字符設備和塊設備。

也可通過下圖理解：

    從上圖可以看出，MTD設備層與原始設備層打交道。通過分析源代碼我們可以知道當上層要求對FLASH進行讀寫時，它會像設備層發出請求，設備層的讀寫函數會調用原始設備層中的讀寫函數，即mtd_info結構體（mtd原始設備層中描述設備的專用結構體）中的讀寫函數，而mtd_info中的函數會調用nand_chip（nand硬件驅動層中描述設備的結構體，其中包含了針對特定設備的基本參數和設備操作函數）中的讀寫函數。所以一個flash硬件驅動程序時的步驟大致如下：

1.  如果FLASH要分區，則定義mtd_partition數組，將FLASH分區信息記錄其中。

mtd_partition friendly_arm_default_nand_part[],arch/arm/plat-s3c24xx/common-friendly-arm.c

2. 在模塊加載時爲每一個chip(主分區)分配mtd_info和nand_chip的內存，根據目標板nand 控制器的特殊情況初始化nand_chip中的實現對FLASH操作的成員函數，如hwcontrol()、dev_ready()、read_byte()、write_byte()等。填充mtd_info,並將其priv成員指向nand_chip。 driver/mtd/nand/s3c2410/c

3. 以mtd_info爲參數調用nand_scan()函數探測NAND FLASH的存在。nand_scan()函數會從FLASH芯片中讀取其參數，填充相應nand_chip成員。 driver/mtd/nand/nand_base/c

nand_scan()分爲兩步，首先是nand_scan_ident(),主要完成flashID的讀取等，然後是nand_scan_tail(),主要完成chip結構體中未初始化函數的默認賦值，以及壞塊的掃描。

4. 如果要分區，則以mtd_info和mtd_partition爲參數調用add_mtd_partions(),添加分區信息。在這個函數裏面會爲每一個分區分配一個mtd_info結構體填充，並註冊。

 

 

二、nand flash驅動程序實例分析

     我們以2.6.29內核中mini2440的nand flash驅動程序爲例來分析一下這個過程，這裏的flash驅動被寫成了platform驅動的形式。我們下面分析其過程：

1. 註冊nand flash設備

 nand flash分區：

 

//arch/arm/plat-s3c24xx/common-friendly-arm.c static struct mtd_partition friendly_arm_default_nand_part[] = { [0] = { .name = "supervivi", .size = 0x00060000, .offset = 0, }, [1] = { .name = "Kernel", .offset = 0x00060000, .size = 0x00200000, }, [2] = { .name = "root", .offset = 0x00260000, .size = 1024 * 1024 * 1024, //64U * 1024 * 1024 - 0x00260000, }, [3] = { .name = "nand", .offset = 0x00000000, .size = 1024 * 1024 * 1024, //64U * 1024 * 1024 - 0x00260000, } }; static struct s3c2410_nand_set friendly_arm_nand_sets[] = { [0] = { .name = "NAND", .nr_chips = 1, //系統只有一個chip .nr_partitions = ARRAY_SIZE(friendly_arm_default_nand_part), // 4個分區 .partitions = friendly_arm_default_nand_part, }, }; static struct s3c2410_platform_nand friendly_arm_nand_info = { .tacls = 20,//2440 rNFCONF 需要設置的時鐘信息 .twrph0 = 60, .twrph1 = 20, .nr_sets = ARRAY_SIZE(friendly_arm_nand_sets), .sets = friendly_arm_nand_sets, };//這裏將許多數據作爲platform_data傳入包括chip數組  

nand控制器資源

//arch/arm/plat-s3c24xx/devs.c static struct resource s3c_nand_resource[] = { [0] = { .start = S3C24XX_PA_NAND, .end = S3C24XX_PA_NAND + S3C24XX_SZ_NAND - 1, .flags = IORESOURCE_MEM, } }; struct platform_device s3c_device_nand = { .name = "s3c2410-nand", .id = -1, .num_resources = ARRAY_SIZE(s3c_nand_resource), .resource = s3c_nand_resource, }; //註冊nand flash作爲platform device: static struct platform_device __initdata *friendly_arm_devs[] = { &s3c_device_nand, &s3c_device_sdi, &s3c_device_usbgadget, }; void __init friendly_arm_machine_init(void) { /* Configure the LEDs (even if we have no LED support)*/ s3c_device_nand.dev.platform_data = &friendly_arm_nand_info; //在nand的驅動程序的probe中會利用這個負責，以及後面添加分區是獲取分區信息 platform_add_devices(friendly_arm_devs, ARRAY_SIZE(friendly_arm_devs)); s3c2410_pm_init(); }  

2.註冊nand flash driver

//linux/drivers/mtd/nand/s3c2410.c static struct platform_driver s3c2440_nand_driver = { .probe = s3c2440_nand_probe, .remove = s3c2410_nand_remove, .suspend = s3c24xx_nand_suspend, .resume = s3c24xx_nand_resume, .driver = { .name = "s3c2440-nand", .owner = THIS_MODULE, }, }; static int __init s3c2410_nand_init(void) { printk("S3C24XX NAND Driver, (c) 2004 Simtec Electronics/n"); platform_driver_register(&s3c2412_nand_driver); platform_driver_register(&s3c2440_nand_driver); return platform_driver_register(&s3c2410_nand_driver); }  

 

        當platform_driver驅動被加載時或者是當platform_device被註冊時，總線驅動程序

 

會查找與設備匹配的驅動程序，找到時設備驅動程序的probe函數會被調用，下面我們來分析一下在我們驅動程序中的probe函數

probe的具體調用流程見 Linux NAND FLASH驅動代碼分析

static int s3c2440_nand_probe(struct platform_device *dev) { return s3c24xx_nand_probe(dev, TYPE_S3C2440); } /* s3c2410_nand_probe * * called by device layer when it finds a device matching * one our driver can handled. This code checks to see if * it can allocate all necessary resources then calls the * nand layer to look for devices */ static int s3c24xx_nand_probe(struct platform_device *pdev, enum s3c_cpu_type cpu_type) { struct s3c2410_platform_nand *plat = to_nand_plat(pdev); struct s3c2410_nand_info *info; struct s3c2410_nand_mtd *nmtd; struct s3c2410_nand_set *sets; struct resource *res; int err = 0; int size; int nr_sets; int setno; pr_debug("s3c2410_nand_probe(%p)/n", pdev); info = kmalloc(sizeof(*info), GFP_KERNEL); //分配s3c2410_nand_info內存 if (info == NULL) { dev_err(&pdev->dev, "no memory for flash info/n"); err = -ENOMEM; goto exit_error; } memset(info, 0, sizeof(*info)); platform_set_drvdata(pdev, info); spin_lock_init(&info->controller.lock); init_waitqueue_head(&info->controller.wq); /* get the clock source and enable it */ info->clk = clk_get(&pdev->dev, "nand"); if (IS_ERR(info->clk)) { dev_err(&pdev->dev, "failed to get clock/n"); err = -ENOENT; goto exit_error; } clk_enable(info->clk); /* allocate and map the resource */ /* currently we assume we have the one resource */ res = pdev->resource; size = res->end - res->start + 1; info->area = request_mem_region(res->start, size, pdev->name); if (info->area == NULL) { dev_err(&pdev->dev, "cannot reserve register region/n"); err = -ENOENT; goto exit_error; } info->device = &pdev->dev; info->platform = plat; info->regs = ioremap(res->start, size);//存儲Nand控制器的虛擬地址 info->cpu_type = cpu_type; if (info->regs == NULL) { dev_err(&pdev->dev, "cannot reserve register region/n"); err = -EIO; goto exit_error; } dev_dbg(&pdev->dev, "mapped registers at %p/n", info->regs); /* initialise the hardware */ err = s3c2410_nand_inithw(info);//初始化硬件，設置TACLS,TWRPH0/1(2440-rNFCONF)並使能nand控制器 if (err != 0) goto exit_error; sets = (plat != NULL) ? plat->sets : NULL; nr_sets = (plat != NULL) ? plat->nr_sets : 1; info->mtd_count = nr_sets;//1 /* allocate our information */ size = nr_sets * sizeof(*info->mtds);//nr_sets = 1 info->mtds = kmalloc(size, GFP_KERNEL); if (info->mtds == NULL) { dev_err(&pdev->dev, "failed to allocate mtd storage/n"); err = -ENOMEM; goto exit_error; } memset(info->mtds, 0, size); /* initialise all possible chips */ nmtd = info->mtds; for (setno = 0; setno < nr_sets; setno++, nmtd++) {//nr_sets = 1 pr_debug("initialising set %d (%p, info %p)/n", setno, nmtd, info); //初始化nand_chip中的read_buf,write_buf等函數指針,ecc設置 s3c2410_nand_init_chip(info, nmtd, sets); //nand_scan()的第一步(nand_base.c),read ID… nmtd->scan_res = nand_scan_ident(&nmtd->mtd, (sets) ? sets->nr_chips : 1); if (nmtd->scan_res == 0) { //如果使用硬件ecc，根據id信息中的page大小更新ecc設置 s3c2410_nand_update_chip(info, nmtd); //nand_scan()的第二步(nand_base.c),給初始化的函數指針默認值，掃描壞塊 nand_scan_tail(&nmtd->mtd); s3c2410_nand_add_partition(info, nmtd, sets);//添加分區，想mtd註冊分區信息 } if (sets != NULL) sets++; } err = s3c2410_nand_cpufreq_register(info); if (err < 0) { dev_err(&pdev->dev, "failed to init cpufreq support/n"); goto exit_error; } if (allow_clk_stop(info)) { dev_info(&pdev->dev, "clock idle support enabled/n"); clk_disable(info->clk); } pr_debug("initialised ok/n"); return 0; exit_error: s3c2410_nand_remove(pdev); if (err == 0) err = -EINVAL; return err; }