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，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;
};
本篇文章来源于 Linux公社网站(www.linuxidc.com) 原文链接：http://www.linuxidc.com/Linux/2011-01/31293.htm
