Linux NAND FLASH驅動程序框架分析

1.Linux-MTD Subsystem

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。

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)，另外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系統能夠定義出MTD的塊設備（主設備號31）www.linuxidc.com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：經過mknod在/dev子目錄下創建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），用戶經過訪問此設備節點便可訪問MTD字符設備和塊設備。

也可經過下圖理解：

從上圖能夠看出，MTD設備層與原始設備層打交道。經過分析源代碼咱們能夠知道當上層要求對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做函數）中的讀寫函數。因此當咱們寫一個 flash硬件驅動程序時，有如下步驟：

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

2. 在模塊加載時爲每個chip(主分區)分配mtd_info和nand_chip的內存，根據目標板nand 控制器的特殊狀況初始化nand_chip中的實現對FLASH操做的成員函數，如hwcontrol()、dev_ready()、 read_byte()、write_byte()等。填充mtd_info,並將其priv成員指向nand_chip。

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。

4. 若是要分區，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個分區（不包含主分區）分配一個mtd_info結構體，www.linuxidc.com填充，並註冊。

2.nand flash驅動程序實例分析

咱們以2.6.26內核中s3c2410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。咱們下面分析其過程：

1. 註冊nand flash設備

nand flash分區：

linux2.6.26.8/arch/arm/plat-s3c24xx/common-smdk.c:

static struct mtd_partition smdk_default_nand_part[] = {

[0] = {

name: "bootloader",

size: 0x00100000,

offset: 0x0,

},

[1] = {

name: "kernel",

size: 0x00300000,

offset: 0x00100000,

},

[2] = {

name: "root",

size: 0x02800000,

offset: 0x00400000,

},

};

static struct s3c2410_nand_set smdk_nand_sets[] = {  //該數組爲chip集合，這裏咱們只有一片chip

[0] = {

.name = "NAND",

.nr_chips = 1,

.nr_partitions = ARRAY_SIZE(smdk_default_nand_part),

.partitions = smdk_default_nand_part,

},

};

static struct s3c2410_platform_nand smdk_nand_info = {  //這裏將許多數據做爲platform_data傳入包括chip數組

.tacls = 20,

.twrph0 = 60,

.twrph1 = 20,

.nr_sets = ARRAY_SIZE(smdk_nand_sets),

.sets = smdk_nand_sets,

};

nand控制器資源：

linux2.6.26.8/arch/arm/plat-s3c24xx/devs.c

static struct resource s3c_nand_resource[] = {

[0] = {

.start = S3C2410_PA_NAND,

.end   = S3C2410_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做爲platform device:

linux2.6.26.8/arch/arm/plat-s3c24xx/common-smdk.c:

static struct platform_device __initdata *smdk_devs[] = {

&s3c_device_nand,

…

};

void __init smdk_machine_init(void)

{

…

s3c_device_nand.dev.platform_data = &smdk_nand_info;   //注意這裏的賦值，在nand  flash驅動程序的probe函數裏面利用了這裏賦值的數據

platform_add_devices(smdk_devs, ARRAY_SIZE(smdk_devs));

s3c2410_pm_init();

}

2. 註冊nand flash driver
linux/drivers/mtd/nand/s3c2410.c:

static struct platform_driver s3c2410_nand_driver = {

.probe = s3c2410_nand_probe,

.remove = s3c2410_nand_remove,

.suspend = s3c24xx_nand_suspend,

.resume = s3c24xx_nand_resume,

.driver = {

.name = "s3c2410-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);

}

module_init(s3c2410_nand_init);

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，下面咱們來分析一下在咱們驅動程序中的probe函數：

static int s3c2410_nand_probe(struct platform_device *dev)

{

return s3c24xx_nand_probe(dev, TYPE_S3C2410);

}

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;

}

 

memzero(info, sizeof(*info));         //將s3c2410_nand_info清零

platform_set_drvdata(pdev, info); //pdev->dev->driver_data = info

 

spin_lock_init(&info->controller.lock);

init_waitqueue_head(&info->controller.wq);

 

 

 

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);

 

 

 

 

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控制器寄存器虛擬地

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);

 

 

 

err = s3c2410_nand_inithw(info, pdev);  //設置TACLS TWRPH0 TWRPH1

if (err != 0)

goto exit_error;

 

sets = (plat != NULL) ? plat->sets : NULL;    //sets指向plat->sets數組的首地址

nr_sets = (plat != NULL) ? plat->nr_sets : 1;   //plat->sets中的chips數目

 

info->mtd_count = nr_sets;

size = nr_sets * sizeof(*info->mtds);     

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;

}

memzero(info->mtds, size); //將申請的s3c2410_nand_mtd結構體數組清零

nmtd = info->mtds;

for (setno = 0; setno < nr_sets; setno++, nmtd++) {

pr_debug("initialising set %d (%p, info %p)\n", setno, nmtd, info);

 

s3c2410_nand_init_chip(info, nmtd, sets); //初始化s3c2410_nand_mtd結構

體中的chip成員和mtd成員,且mtd.priv = chip

 

nmtd->scan_res = nand_scan_ident(&nmtd->mtd,

 (sets) ? sets->nr_chips : 1); //設置nand_chip一些成員

的默認值並探測FLASH,並讀出FLASH參數，填入nand_chip

 

if (nmtd->scan_res == 0) {

s3c2410_nand_update_chip(info, nmtd); //

nand_scan_tail(&nmtd->mtd);   //設置nand_chip中全部未被設置的

函數指針的值，並填充相關mtd_info成員，若須要創建bad block table

s3c2410_nand_add_partition(info, nmtd, sets);  //添加分區

}

 

if (sets != NULL)

sets++; //注意這裏sets++,指向下一個plat->sets裏的set

}

 

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;

}

 

struct mtd_info {

u_char type;

u_int32_t flags;

u_int32_t size;  // Total size of the MTD

 

 

u_int32_t erasesize;

 

u_int32_t writesize;

 

u_int32_t oobsize;   // Amount of OOB data per block (e.g. 16)

u_int32_t oobavail;  // Available OOB bytes per block

 

// Kernel-only stuff starts here.

char *name;

int index;

 

 

struct nand_ecclayout *ecclayout;

 

 

int numeraseregions;

struct mtd_erase_region_info *eraseregions;

 

 

int (*erase) (struct mtd_info *mtd, struct erase_info *instr);

 

 

 

int (*point) (struct mtd_info *mtd, loff_t from, size_t len,

size_t *retlen, void **virt, resource_size_t *phys);

 

 

void (*unpoint) (struct mtd_info *mtd, loff_t from, size_t len);

 

 

int (*read) (struct mtd_info *mtd, loff_t from, size_t len, size_t *retlen, u_char *buf);

int (*write) (struct mtd_info *mtd, loff_t to, size_t len, size_t *retlen, const u_char *buf);

 

 

 

int (*panic_write) (struct mtd_info *mtd, loff_t to, size_t len, size_t *retlen, const u_char *buf);

 

int (*read_oob) (struct mtd_info *mtd, loff_t from,

 struct mtd_oob_ops *ops);

int (*write_oob) (struct mtd_info *mtd, loff_t to,

 struct mtd_oob_ops *ops);

 

 

int (*get_fact_prot_info) (struct mtd_info *mtd, struct otp_info *buf, size_t len);

int (*read_fact_prot_reg) (struct mtd_info *mtd, loff_t from, size_t len, size_t *retlen, u_char *buf);

int (*get_user_prot_info) (struct mtd_info *mtd, struct otp_info *buf, size_t len);

int (*read_user_prot_reg) (struct mtd_info *mtd, loff_t from, size_t len, size_t *retlen, u_char *buf);

int (*write_user_prot_reg) (struct mtd_info *mtd, loff_t from, size_t len, size_t *retlen, u_char *buf);

int (*lock_user_prot_reg) (struct mtd_info *mtd, loff_t from, size_t len);

 

 

int (*writev) (struct mtd_info *mtd, const struct kvec *vecs, unsigned long count, loff_t to, size_t *retlen);

 

 

void (*sync) (struct mtd_info *mtd);

 

 

int (*lock) (struct mtd_info *mtd, loff_t ofs, size_t len);

int (*unlock) (struct mtd_info *mtd, loff_t ofs, size_t len);

 

 

int (*suspend) (struct mtd_info *mtd);

void (*resume) (struct mtd_info *mtd);

 

 

int (*block_isbad) (struct mtd_info *mtd, loff_t ofs);

int (*block_markbad) (struct mtd_info *mtd, loff_t ofs);

 

struct notifier_block reboot_notifier; 

 

 

struct mtd_ecc_stats ecc_stats;

 

int subpage_sft;

 

void *priv;

 

struct module *owner;

int usecount;

 

 

int (*get_device) (struct mtd_info *mtd);

void (*put_device) (struct mtd_info *mtd);

};

 

struct nand_chip {

void  __iomem *IO_ADDR_R;

void  __iomem *IO_ADDR_W;

 

uint8_t (*read_byte)(struct mtd_info *mtd);

u16 (*read_word)(struct mtd_info *mtd);

void (*write_buf)(struct mtd_info *mtd, const uint8_t *buf, int len);

void (*read_buf)(struct mtd_info *mtd, uint8_t *buf, int len);

int (*verify_buf)(struct mtd_info *mtd, const uint8_t *buf, int len);

void (*select_chip)(struct mtd_info *mtd, int chip);

int (*block_bad)(struct mtd_info *mtd, loff_t ofs, int getchip);

int (*block_markbad)(struct mtd_info *mtd, loff_t ofs);

void (*cmd_ctrl)(struct mtd_info *mtd, int dat,

    unsigned int ctrl);

int (*dev_ready)(struct mtd_info *mtd);

void (*cmdfunc)(struct mtd_info *mtd, unsigned command, int column, int page_addr);

int (*waitfunc)(struct mtd_info *mtd, struct nand_chip *this);

void (*erase_cmd)(struct mtd_info *mtd, int page);

int (*scan_bbt)(struct mtd_info *mtd);

int (*errstat)(struct mtd_info *mtd, struct nand_chip *this, int state, int status, int page);

int (*write_page)(struct mtd_info *mtd, struct nand_chip *chip,

      const uint8_t *buf, int page, int cached, int raw);

 

int chip_delay;

unsigned int options;

 

int page_shift;

int phys_erase_shift;

int bbt_erase_shift;

int chip_shift;

int numchips;

unsigned long chipsize;

int pagemask;

int pagebuf;

int subpagesize;

uint8_t cellinfo;

int badblockpos;

 

nand_state_t state;

 

uint8_t *oob_poi;

struct nand_hw_control  *controller;

struct nand_ecclayout *ecclayout;

 

struct nand_ecc_ctrl ecc;

struct nand_buffers *buffers;

struct nand_hw_control hwcontrol;

 

struct mtd_oob_ops ops;

 

uint8_t *bbt;

struct nand_bbt_descr *bbt_td;

struct nand_bbt_descr *bbt_md;

 

struct nand_bbt_descr *badblock_pattern;

 

void *priv;

};