Linux NAND FLASH驱动程序框架分析

1.Linux-MTD Subsystem

FLASH在嵌入式系统中是必不可少的，它是bootloader、linux内核和文件系统的最佳载体。在Linux内核中引入了MTD子系统为NOR FLASH和NAND FLASH设备提供统一的接口，从而使得FLASH驱动的设计大为简化。

在引入MTD后Linux系统中FLASH设备驱动可分为四层，如图：

1. 硬件驱动层

FLASH硬件驱动层负责FLASH硬件设备的读、写、擦出，LINUX MTD设备的NOR FLASH驱动位于/driver/mtd/chips子目录下，NAND FLASH驱动则位于/driver/mtd/nand子目录下。

2. MTD原始设备层：MTD原始设备层由两部分构成，一部分是MTD原始设备的通用代码(mtdcore.c、mtdpart.c)，另一部分是各个特定的FLASH的数据，例如分区。

3. MTD设备层：基于MTD原始设备，LINUX系统可以定义出MTD的块设备（主设备号31）www.linuxidc.com和字符设备（设备号90），构成设备层。MTD字符设备在mtdchar.c实现，MTD块设备在mtdblock.c实现。

4. 设备节点：通过mknod在/dev子目录下建立MTD字符设备节点（主设备号为90）和块设备节点（主设备号为31），用户通过访问此设备节点即可访问MTD字符设备和块设备。

也可通过下图理解：

从上图可以看出，MTD设备层与原始设备层打交道。通过分析源代码我们可以知道当上层要求对FLASH进行读写时，它会像设备层发出请求，设备层的 读写函数会调用原始设备层中的读写函数，即mtd_info结构体（mtd原始设备层中描述设备的专用结构体）中的读写函数，而mtd_info中的函数 会调用nand_chip（nand硬件驱动层中描述设备的结构体，其中包含了针对特定设备的基本参数和设备操作函数）中的读写函数。所以当我们写一个 flash硬件驱动程序时，有以下步骤：

1. 如果FLASH要分区，则定义mtd_partition数组，将FLASH分区信息记录其中。

2. 在模块加载时为每一个chip(主分区)分配mtd_info和nand_chip的内存，根据目标板nand 控制器的特殊情况初始化nand_chip中的实现对FLASH操作的成员函数，如hwcontrol()、dev_ready()、 read_byte()、write_byte()等。填充mtd_info,并将其priv成员指向nand_chip。

3. 以mtd_info为参数调用nand_scan()函数探测NAND FLASH的存在。nand_scan()函数会从FLASH芯片中读取其参数，填充相应nand_chip成员。

4. 如果要分区，则以mtd_info和mtd_partition为参数调用add_mtd_partions(),添加分区信息。在这个函数里面会为每一个分区（不包含主分区）分配一个mtd_info结构体，www.linuxidc.com填充，并注册。

2.nand flash驱动程序实例分析

我们以2.6.26内核中s3c2410的nand flash驱动程序为例来分析一下这个过程，这里的flash驱动被写成了platform驱动的形式。我们下面分析其过程：

1. 注册nand flash设备

nand flash分区：

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[] = {  //该数组为chip集合，这里我们只有一片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 = {  //这里将许多数据作为platform_data传入包括chip数组

.tacls = 20,

.twrph0 = 60,

.twrph1 = 20,

.nr_sets = ARRAY_SIZE(smdk_nand_sets),

.sets = smdk_nand_sets,

};

nand控制器资源：

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,

};

注册nand flash作为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;   //注意这里的赋值，在nand  flash驱动程序的probe函数里面利用了这里赋值的数据

platform_add_devices(smdk_devs, ARRAY_SIZE(smdk_devs));

s3c2410_pm_init();

}

2. 注册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);

当platform_driver驱动被加载时或者是当platform_device被注册时，总线驱动程序

会查找与设备匹配的驱动程序，找到时设备驱动程序的probe函数会被调用，下面我们来分析一下在我们驱动程序中的probe函数：

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内存

if (info == NULL) {

dev_err(&pdev->dev, "no memory for flash info/n");

err = -ENOMEM;

goto exit_error;

}

 

memzero(info, sizeof(*info));         //将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);  //存储nand控制器寄存器虚拟地

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);  //设置TACLS TWRPH0 TWRPH1

if (err != 0)

goto exit_error;

 

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

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

 

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); //将申请的s3c2410_nand_mtd结构体数组清零

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结构

体中的chip成员和mtd成员,且mtd.priv = chip

 

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

 (sets) ? sets->nr_chips : 1); //设置nand_chip一些成员

的默认值并探测FLASH,并读出FLASH参数，填入nand_chip

 

if (nmtd->scan_res == 0) {

s3c2410_nand_update_chip(info, nmtd); //

nand_scan_tail(&nmtd->mtd);   //设置nand_chip中所有未被设置的

函数指针的值，并填充相关mtd_info成员，若需要建立bad block table

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

}

 

if (sets != NULL)

sets++; //注意这里sets++,指向下一个plat->sets里的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;

}

 

 

附：几个机构体

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; };