MTD原始设备与FLASH硬件驱动的对话
看了<<Linux MTD源代码分析>>后对以MTD的分层结构以及各层的分工情况有了大致的了解，然而各层之间是如何进行对话的呢，对于这个问题，<<Linux MTD源代码分析>>上没有详细的去说明。
小弟抽空研究了一下，打算从下到上，在从上到下，分两条主线来研究一下MTD原始设备与FLASH硬件驱动的对话(MTD原始设备与更上层的对话留待以后再研究)。
以下是第一部分，从下到上的介绍FLASH硬件驱动与MTD原始设备是如何建立联系的。
1、首先从入口函数开始：
static int s3c24xx_nand_probe (struct device *dev, int is_s3c2440)
{
struct platform_device *pdev = to_platform_device(dev);
struct s3c2410_platform_nand *plat = to_nand_plat(dev);
//获取nand flash配置用结构体数据(dev.c中定义，详细见附录部分)
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", dev);
info = kmalloc(sizeof(*info), GFP_KERNEL);
if (info == NULL) {
printk(KERN_ERR PFX "no memory for flash info/n");
err = -ENOMEM;
goto exit_error;
}
memzero(info, sizeof(*info));
dev_set_drvdata(dev, info); //以后有用
spin_lock_init(&info->controller.lock); //初始化自旋锁
init_waitqueue_head(&info->controller.wq); //初始化等待队列
/* get the clock source and enable it */
info->clk = clk_get(dev, "nand");
if (IS_ERR(info->clk)) {
printk(KERN_ERR PFX "failed to get clock");
err = -ENOENT;
goto exit_error;
}
clk_use(info->clk);
clk_enable(info->clk);
/* allocate and map the resource */
/* currently we assume we have the one resource */
res = pdev->resource; //提取dev.c中定义的与设备相关的资源
size = res->end - res->start + 1;
info->area = request_mem_region(res->start, size, pdev->name);
if (info->area == NULL) {
printk(KERN_ERR PFX "cannot reserve register region/n");
err = -ENOENT;
goto exit_error;
}
info->device = dev;
info->platform = plat; //保存好struct s3c2410_platform_nand结构数据
info->regs = ioremap(res->start, size);//映射nand flash用到的寄存器
info->is_s3c2440 = is_s3c2440;
if (info->regs == NULL) {
printk(KERN_ERR PFX "cannot reserve register region/n");
err = -EIO;
goto exit_error;
}
printk(KERN_INFO PFX "mapped registers at %p/n", info->regs);
/* initialise the hardware */
err = s3c2410_nand_inithw(info, dev);
//初始化s3c2410 nand flash控制，主要是配置S3C2410_NFCONF寄存器
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;
//我的板上只有一块nand flash，配置信息见plat-sets，数目为1。
/* allocate our information */
size = nr_sets * sizeof(*info->mtds);
info->mtds = kmalloc(size, GFP_KERNEL);
if (info->mtds == NULL) {
printk(KERN_ERR PFX "failed to allocate mtd storage/n");
err = -ENOMEM;
goto exit_error;
}
memzero(info->mtds, size);
/* initialise all possible chips */
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);
nmtd->scan_res = nand_scan(&nmtd->mtd,
(sets) ? sets->nr_chips : 1);//为什么使用set->nr_chips(还没配置的东西)？
if (nmtd->scan_res == 0) {
s3c2410_nand_add_partition(info, nmtd, sets);
}
if (sets != NULL)
sets++;
}
pr_debug("initialised ok/n");
return 0;
exit_error:
s3c2410_nand_remove(dev);
if (err == 0)
err = -EINVAL;
return err;
}
//初始化代表一片flash的struct nand_chip结构
static void s3c2410_nand_init_chip (struct s3c2410_nand_info *info,
struct s3c2410_nand_mtd *nmtd,
struct s3c2410_nand_set *set)
{
struct nand_chip *chip = &nmtd->chip;
chip->IO_ADDR_R = info->regs + S3C2410_NFDATA; //读地址
chip->IO_ADDR_W = info->regs + S3C2410_NFDATA; //写地址
chip->hwcontrol = s3c2410_nand_hwcontrol;
chip->dev_ready = s3c2410_nand_devready; //ready状态查询
chip->write_buf = s3c2410_nand_write_buf; //写函数
chip->read_buf = s3c2410_nand_read_buf; //读函数
chip->select_chip = s3c2410_nand_select_chip; //片选函数
chip->chip_delay = 50;
chip->priv = nmtd;
chip->options = 0;
chip->controller = &info->controller;
if (info->is_s3c2440) {
chip->IO_ADDR_R = info->regs + S3C2440_NFDATA;
chip->IO_ADDR_W = info->regs + S3C2440_NFDATA;
chip->hwcontrol = s3c2440_nand_hwcontrol;
}
nmtd->info = info;
nmtd->mtd.priv = chip;
//nand_scan函数中会调用struct nand_chip *this = mtd->priv取出该struct nand_chip结构
nmtd->set = set;
if (hardware_ecc) {
chip->correct_data = s3c2410_nand_correct_data;
chip->enable_hwecc = s3c2410_nand_enable_hwecc;
chip->calculate_ecc = s3c2410_nand_calculate_ecc;
chip->eccmode = NAND_ECC_HW3_512;
chip->autooob = &nand_hw_eccoob;
if (info->is_s3c2440) {
chip->enable_hwecc = s3c2440_nand_enable_hwecc;
chip->calculate_ecc = s3c2440_nand_calculate_ecc;
}
} else {
chip->eccmode = NAND_ECC_SOFT; //ECC的类型
}
}
/* command and control functions
*
* Note, these all use tglx's method of changing the IO_ADDR_W field
* to make the code simpler, and use the nand layer's code to issue the
* command and address sequences via the proper IO ports.
*
*/
static void s3c2410_nand_hwcontrol (struct mtd_info *mtd, int cmd)
{
struct s3c2410_nand_info *info = s3c2410_nand_mtd_toinfo(mtd);
struct nand_chip *chip = mtd->priv;
switch (cmd) {
case NAND_CTL_SETNCE:
case NAND_CTL_CLRNCE:
printk(KERN_ERR "%s: called for NCE/n", __FUNCTION__);
break;
case NAND_CTL_SETCLE:
chip->IO_ADDR_W = info->regs + S3C2410_NFCMD;//写命令
break;
case NAND_CTL_SETALE:
chip->IO_ADDR_W = info->regs + S3C2410_NFADDR;//写地址
break;
/* NAND_CTL_CLRCLE: */
/* NAND_CTL_CLRALE: */
default:
chip->IO_ADDR_W = info->regs + S3C2410_NFDATA;//写数据
break;
}
}
/* s3c2410_nand_devready()
*
* returns 0 if the nand is busy, 1 if it is ready
*/
static int s3c2410_nand_devready (struct mtd_info *mtd)
{
struct s3c2410_nand_info *info = s3c2410_nand_mtd_toinfo(mtd);
if (info->is_s3c2440)
return readb(info->regs + S3C2440_NFSTAT) & S3C2440_NFSTAT_READY;
return readb(info->regs + S3C2410_NFSTAT) & S3C2410_NFSTAT_BUSY;//返回nand flash都忙标志
}
static void s3c2410_nand_write_buf (struct mtd_info *mtd,
const u_char *buf, int len)
{
struct nand_chip *this = mtd->priv;
writesb(this->IO_ADDR_W, buf, len);//写操作
}
static void s3c2410_nand_read_buf (struct mtd_info *mtd, u_char *buf, int len)
{
struct nand_chip *this = mtd->priv;
readsb(this->IO_ADDR_R, buf, len);//读操作
}
/* select chip */
/*
* 根据chip都值设置nand flash都片选信号:
* chip = -1 -- 禁用nand flash
* chip !=-1 -- 选择对应的nand flash
*/
static void s3c2410_nand_select_chip (struct mtd_info *mtd, int chip)
{
struct s3c2410_nand_info *info;
struct s3c2410_nand_mtd *nmtd;
struct nand_chip *this = mtd->priv;
void __iomem *reg;
unsigned long cur;
unsigned long bit;
nmtd = this->priv;
info = nmtd->info;
bit = (info->is_s3c2440) ? S3C2440_NFCONT_nFCE : S3C2410_NFCONF_nFCE;
reg = info->regs+((info->is_s3c2440) ? S3C2440_NFCONT:S3C2410_NFCONF);
cur = readl(reg);
if (chip == -1) {
cur |= bit;
} else {
if (nmtd->set != NULL && chip > nmtd->set->nr_chips) {
printk(KERN_ERR PFX "chip %d out of range/n", chip);
return;
}
if (info->platform != NULL) {
if (info->platform->select_chip != NULL)
(info->platform->select_chip)(nmtd->set, chip);
}
cur &= ~bit;
}
writel(cur, reg);
}
注：
s3c2410_nand_init_chip填充struct nand_chip的一部分成员，nand_scan以通用nand flash的标准进行检测，并填充struct nand_chip的其它成员，必要时根据检测结果进行取舍。
int nand_scan (struct mtd_info *mtd, int maxchips)
{
int i, nand_maf_id, nand_dev_id, busw, maf_id;
struct nand_chip *this = mtd->priv; //取出struct nand_chip结构
/* Get buswidth to select the correct functions*/
busw = this->options & NAND_BUSWIDTH_16; //nand flash的位宽
/* check for proper chip_delay setup, set 20us if not */
if (!this->chip_delay)
this->chip_delay = 20;
/* check, if a user supplied command function given */
if (this->cmdfunc == NULL) //填充命令函数
this->cmdfunc = nand_command;
/* check, if a user supplied wait function given */
if (this->waitfunc == NULL) //填充等待函数
this->waitfunc = nand_wait;
if (!this->select_chip) //s3c2410_nand_init_chip中已定义
this->select_chip = nand_select_chip;
if (!this->write_byte) //使用默认的
this->write_byte = busw ? nand_write_byte16 : nand_write_byte;
if (!this->read_byte) //使用默认的
this->read_byte = busw ? nand_read_byte16 : nand_read_byte;
if (!this->write_word) //使用默认的
this->write_word = nand_write_word;
if (!this->read_word) //使用默认的
this->read_word = nand_read_word;
if (!this->block_bad) //使用默认的
this->block_bad = nand_block_bad;
if (!this->block_markbad) //使用默认的
this->block_markbad = nand_default_block_markbad;
if (!this->write_buf) //s3c2410_nand_init_chip中已定义
this->write_buf = busw ? nand_write_buf16 : nand_write_buf;
if (!this->read_buf) //s3c2410_nand_init_chip中已定义
this->read_buf = busw ? nand_read_buf16 : nand_read_buf;
if (!this->verify_buf) //使用默认的
this->verify_buf = busw ? nand_verify_buf16 : nand_verify_buf;
if (!this->scan_bbt) //使用默认的
this->scan_bbt = nand_default_bbt;
/* Select the device */
this->select_chip(mtd, 0); //片选，可惜在s3c2410 nand flash控制器中此操作为空
/* Send the command for reading device ID */
this->cmdfunc (mtd, NAND_CMD_READID, 0x00, -1);//发送读ID命令
/* Read manufacturer and device IDs */
nand_maf_id = this->read_byte(mtd); //读取生产商ID
nand_dev_id = this->read_byte(mtd); //读取设备ID
/* Print and store flash device information */
for (i = 0; nand_flash_ids[i].name != NULL; i++) {
//保存着nand flash资料的nand_flash_ids表在include/linux/mtd/nand_ids.c文件中，详细见附录
if (nand_dev_id != nand_flash_ids[i].id) //比较设备ID
continue;
if (!mtd->name) mtd->name = nand_flash_ids[i].name; //填充设备名
this->chipsize = nand_flash_ids[i].chipsize << 20; //填充设备大小
/* New devices have all the information in additional id bytes */
if (!nand_flash_ids[i].pagesize) {
int extid;
/* The 3rd id byte contains non relevant data ATM */
extid = this->read_byte(mtd);
/* The 4th id byte is the important one */
extid = this->read_byte(mtd);
/* Calc pagesize */
mtd->oobblock = 1024 << (extid & 0x3);
extid >>= 2;
/* Calc oobsize */
mtd->oobsize = (8 << (extid & 0x03)) * (mtd->oobblock / 512);
extid >>= 2;
/* Calc blocksize. Blocksize is multiples of 64KiB */
mtd->erasesize = (64 * 1024) << (extid & 0x03);
extid >>= 2;
/* Get buswidth information */
busw = (extid & 0x01) ? NAND_BUSWIDTH_16 : 0;
} else {
/* Old devices have this data hardcoded in the
* device id table */
mtd->erasesize = nand_flash_ids[i].erasesize; //填充檫除单元大小 (16k)
mtd->oobblock = nand_flash_ids[i].pagesize; //填充页大小( 512 )
mtd->oobsize = mtd->oobblock / 32; //oob大小(512/32=16)
busw = nand_flash_ids[i].options & NAND_BUSWIDTH_16;//获取nand flash表中定义的位宽
}
/* Try to identify manufacturer */ //比较生产商ID
for (maf_id = 0; nand_manuf_ids[maf_id].id != 0x0; maf_id++) {
if (nand_manuf_ids[maf_id].id == nand_maf_id)
break;
}
/* Check, if buswidth is correct. Hardware drivers should set
* this correct ! */
/用户定义的位宽与芯片实际的位宽不一致，取消nand flash的片选
if (busw != (this->options & NAND_BUSWIDTH_16)) {
printk (KERN_INFO "NAND device: Manufacturer ID:"
" 0x%02x, Chip ID: 0x%02x (%s %s)/n", nand_maf_id, nand_dev_id,
nand_manuf_ids[maf_id].name , mtd->name);
printk (KERN_WARNING
"NAND bus width %d instead %d bit/n",
(this->options & NAND_BUSWIDTH_16) ? 16 : 8,
busw ? 16 : 8);
this->select_chip(mtd, -1);//在s3c2410 nand flash控制器驱动中，此操作为空操作
return 1;
}
/* Calculate the address shift from the page size */
//计算页、可檫除单元、nand flash大小的偏移值
this->page_shift = ffs(mtd->oobblock) - 1;
this->bbt_erase_shift = this->phys_erase_shift = ffs(mtd->erasesize) - 1;
this->chip_shift = ffs(this->chipsize) - 1;
/* Set the bad block position */
//标注此nand flash为大页还是小页？
this->badblockpos = mtd->oobblock > 512 ?
NAND_LARGE_BADBLOCK_POS : NAND_SMALL_BADBLOCK_POS;
/* Get chip options, preserve non chip based options */
//用户没指定的选项从nand flash表中获取补上
this->options &= ~NAND_CHIPOPTIONS_MSK;
this->options |= nand_flash_ids[i].options & NAND_CHIPOPTIONS_MSK;
/* Set this as a default. Board drivers can override it, if neccecary */
this->options |= NAND_NO_AUTOINCR;
/* Check if this is a not a samsung device. Do not clear the options
* for chips which are not having an extended id.
*/
if (nand_maf_id != NAND_MFR_SAMSUNG && !nand_flash_ids[i].pagesize)
this->options &= ~NAND_SAMSUNG_LP_OPTIONS;
/* Check for AND chips with 4 page planes */
if (this->options & NAND_4PAGE_ARRAY)
this->erase_cmd = multi_erase_cmd;
else
this->erase_cmd = single_erase_cmd;
/* Do not replace user supplied command function ! */
if (mtd->oobblock > 512 && this->cmdfunc == nand_command)
this->cmdfunc = nand_command_lp;
printk (KERN_INFO "NAND device: Manufacturer ID:"
" 0x%02x, Chip ID: 0x%02x (%s %s)/n", nand_maf_id, nand_dev_id,
nand_manuf_ids[maf_id].name , nand_flash_ids[i].name);
break;
}//好的，检测结束^_^
if (!nand_flash_ids[i].name) {
printk (KERN_WARNING "No NAND device found!!!/n");
this->select_chip(mtd, -1);
return 1;
}
//统计一下同种类型的nand flash有多少块(我板上只有一块)
for (i=1; i < maxchips; i++) {
this->select_chip(mtd, i);
/* Send the command for reading device ID */
this->cmdfunc (mtd, NAND_CMD_READID, 0x00, -1);
/* Read manufacturer and device IDs */
if (nand_maf_id != this->read_byte(mtd) ||
nand_dev_id != this->read_byte(mtd))
break;
}
if (i > 1)
printk(KERN_INFO "%d NAND chips detected/n", i);
/* Allocate buffers, if neccecary */
if (!this->oob_buf) {
size_t len;
//求出一个檫除单元64K中oob所占用的总空间
len = mtd->oobsize << (this->phys_erase_shift - this->page_shift);
this->oob_buf = kmalloc (len, GFP_KERNEL);
if (!this->oob_buf) {
printk (KERN_ERR "nand_scan(): Cannot allocate oob_buf/n");
return -ENOMEM;
}
this->options |= NAND_OOBBUF_ALLOC;//oob空间已分配，置相应的标志位
}
if (!this->data_buf) {
size_t len;
len = mtd->oobblock + mtd->oobsize;//512+16=128
this->data_buf = kmalloc (len, GFP_KERNEL);
if (!this->data_buf) {
if (this->options & NAND_OOBBUF_ALLOC)
kfree (this->oob_buf);
printk (KERN_ERR "nand_scan(): Cannot allocate data_buf/n");
return -ENOMEM;
}
this->options |= NAND_DATABUF_ALLOC; //数据空间已分配，置相应的标志位
}
/* Store the number of chips and calc total size for mtd */
this->numchips = i;//记录nand flash片数
mtd->size = i * this->chipsize;//计算出nand flash总大小
/* Convert chipsize to number of pages per chip -1. */
this->pagemask = (this->chipsize >> this->page_shift) - 1;//(64M>>9)-1=128k-1=0x1ffff
/* Preset the internal oob buffer */
//oob_buf全部置为0xff
memset(this->oob_buf, 0xff, mtd->oobsize << (this->phys_erase_shift - this->page_shift));
/* If no default placement scheme is given, select an
* appropriate one */
if (!this->autooob) { //我们选用的是NAND_ECC_SOFT，autooob未设置
/* Select the appropriate default oob placement scheme for
* placement agnostic filesystems */
switch (mtd->oobsize) {
case 8:
this->autooob = &nand_oob_8;
break;
case 16:
this->autooob = &nand_oob_16;//我们的nand flash属于这一类
break;
case 64:
this->autooob = &nand_oob_64;
break;
default:
printk (KERN_WARNING "No oob scheme defined for oobsize %d/n",
mtd->oobsize);
BUG();
}
}
注：
ECC的东西不是很懂，先跳过^_^
/* The number of bytes available for the filesystem to place fs dependend
* oob data */
mtd->oobavail = 0;
for (i = 0; this->autooob->oobfree[i][1]; i++)
mtd->oobavail += this->autooob->oobfree[i][1];
/*
* check ECC mode, default to software
* if 3byte/512byte hardware ECC is selected and we have 256 byte pagesize
* fallback to software ECC
*/
this->eccsize = 256; /* set default eccsize */
this->eccbytes = 3;
switch (this->eccmode) {
case NAND_ECC_HW12_2048:
if (mtd->oobblock < 2048) {
printk(KERN_WARNING "2048 byte HW ECC not possible on %d byte page size, fallback to SW ECC/n",
mtd->oobblock);
this->eccmode = NAND_ECC_SOFT;
this->calculate_ecc = nand_calculate_ecc;
this->correct_data = nand_correct_data;
} else
this->eccsize = 2048;
break;
case NAND_ECC_HW3_512:
case NAND_ECC_HW6_512:
case NAND_ECC_HW8_512:
if (mtd->oobblock == 256) {
printk (KERN_WARNING "512 byte HW ECC not possible on 256 Byte pagesize, fallback to SW ECC /n");
this->eccmode = NAND_ECC_SOFT;
this->calculate_ecc = nand_calculate_ecc;
this->correct_data = nand_correct_data;
} else
this->eccsize = 512; /* set eccsize to 512 */
break;
case NAND_ECC_HW3_256:
break;
case NAND_ECC_NONE:
printk (KERN_WARNING "NAND_ECC_NONE selected by board driver. This is not recommended !!/n");
this->eccmode = NAND_ECC_NONE;
break;
case NAND_ECC_SOFT:
this->calculate_ecc = nand_calculate_ecc;
this->correct_data = nand_correct_data;
break;
default:
printk (KERN_WARNING "Invalid NAND_ECC_MODE %d/n", this->eccmode);
BUG();
}
/* Check hardware ecc function availability and adjust number of ecc bytes per
* calculation step
*/
switch (this->eccmode) {
case NAND_ECC_HW12_2048:
this->eccbytes += 4;
case NAND_ECC_HW8_512:
this->eccbytes += 2;
case NAND_ECC_HW6_512:
this->eccbytes += 3;
case NAND_ECC_HW3_512:
case NAND_ECC_HW3_256:
if (this->calculate_ecc && this->correct_data && this->enable_hwecc)
break;
printk (KERN_WARNING "No ECC functions supplied, Hardware ECC not possible/n");
BUG();
}
mtd->eccsize = this->eccsize;
/* Set the number of read / write steps for one page to ensure ECC generation */
switch (this->eccmode) {
case NAND_ECC_HW12_2048:
this->eccsteps = mtd->oobblock / 2048;
break;
case NAND_ECC_HW3_512:
case NAND_ECC_HW6_512:
case NAND_ECC_HW8_512:
this->eccsteps = mtd->oobblock / 512;
break;
case NAND_ECC_HW3_256:
case NAND_ECC_SOFT:
this->eccsteps = mtd->oobblock / 256;
break;
case NAND_ECC_NONE:
this->eccsteps = 1;
break;
}
/* Initialize state, waitqueue and spinlock */
this->state = FL_READY;
init_waitqueue_head (&this->wq);
spin_lock_init (&this->chip_lock);
/* De-select the device */
this->select_chip(mtd, -1);
/* Invalidate the pagebuffer reference */
this->pagebuf = -1;
/* Fill in remaining MTD driver data */
//填充mtd结构的其它部分
mtd->type = MTD_NANDFLASH;
mtd->flags = MTD_CAP_NANDFLASH | MTD_ECC;
mtd->ecctype = MTD_ECC_SW;
mtd->erase = nand_erase;
mtd->point = NULL;
mtd->unpoint = NULL;
mtd->read = nand_read;
/* nand_read->nand_do_read_ecc->read_buf->s3c2410_nand_read_buf */
mtd->write = nand_write;
/* nand_write->nand_write_ecc->nand_write_page->write_buf->s3c2410_nand_write_buf */
mtd->read_ecc = nand_read_ecc;
mtd->write_ecc = nand_write_ecc;
mtd->read_oob = nand_read_oob;
mtd->write_oob = nand_write_oob;
mtd->readv = NULL;
mtd->writev = nand_writev;
mtd->writev_ecc = nand_writev_ecc;
mtd->sync = nand_sync;
mtd->lock = NULL;
mtd->unlock = NULL;
mtd->suspend = NULL;
mtd->resume = NULL;
mtd->block_isbad = nand_block_isbad;
mtd->block_markbad = nand_block_markbad;
/* and make the autooob the default one */
memcpy(&mtd->oobinfo, this->autooob, sizeof(mtd->oobinfo));
mtd->owner = THIS_MODULE;
/* Check, if we should skip the bad block table scan */
if (this->options & NAND_SKIP_BBTSCAN)
return 0;
/* Build bad block table */
return this->scan_bbt (mtd);
}
/**
* nand_command - [DEFAULT] Send command to NAND device
* @mtd: MTD device structure
* @command: the command to be sent
* @column: the column address for this command, -1 if none
* @page_addr: the page address for this command, -1 if none
*
* Send command to NAND device. This function is used for small page
* devices (256/512 Bytes per page)
*/
static void nand_command (struct mtd_info *mtd, unsigned command, int column, int page_addr)
{
register struct nand_chip *this = mtd->priv;
/* Begin command latch cycle */
this->hwcontrol(mtd, NAND_CTL_SETCLE); //选择写入S3C2410_NFCMD寄存器
/*
* Write out the command to the device.
*/
if (command == NAND_CMD_SEQIN) {
int readcmd;
if (column >= mtd->oobblock) { //读/写位置超出512，读oob_data
/* OOB area */
column -= mtd->oobblock;
readcmd = NAND_CMD_READOOB;
} else if (column < 256) { //读/写位置在前512，使用read0命令
/* First 256 bytes --> READ0 */
readcmd = NAND_CMD_READ0;
} else { //读/写位置在后512，使用read1命令
column -= 256;
readcmd = NAND_CMD_READ1;
}
this->write_byte(mtd, readcmd); //写入具体命令
}
this->write_byte(mtd, command);
/* Set ALE and clear CLE to start address cycle */
/* 清楚CLE，锁存命令；置位ALE，开始传输地址 */
this->hwcontrol(mtd, NAND_CTL_CLRCLE); //锁存命令
if (column != -1 || page_addr != -1) {
this->hwcontrol(mtd, NAND_CTL_SETALE); //选择写入S3C2410_NFADDR寄存器
/* Serially input address */
if (column != -1) {
/* Adjust columns for 16 bit buswidth */
if (this->options & NAND_BUSWIDTH_16)
column >>= 1;
this->write_byte(mtd, column); //写入列地址
}
if (page_addr != -1) { //写入页地址(分三个字节写入)
this->write_byte(mtd, (unsigned char) (page_addr & 0xff));
this->write_byte(mtd, (unsigned char) ((page_addr >> 8) & 0xff));
/* One more address cycle for devices > 32MiB */
if (this->chipsize > (32 << 20))
this->write_byte(mtd, (unsigned char) ((page_addr >> 16) & 0x0f));
}
/* Latch in address */
/* 锁存地址 */
this->hwcontrol(mtd, NAND_CTL_CLRALE);
}
/*
* program and erase have their own busy handlers
* status and sequential in needs no delay
*/
switch (command) {
case NAND_CMD_PAGEPROG:
case NAND_CMD_ERASE1:
case NAND_CMD_ERASE2:
case NAND_CMD_SEQIN:
case NAND_CMD_STATUS:
return;
case NAND_CMD_RESET: //复位操作
// 等待nand flash become ready
if (this->dev_ready) //判断nand flash 是否busy(1:ready 0:busy)
break;
udelay(this->chip_delay);
this->hwcontrol(mtd, NAND_CTL_SETCLE);
this->write_byte(mtd, NAND_CMD_STATUS);
this->hwcontrol(mtd, NAND_CTL_CLRCLE);
while ( !(this->read_byte(mtd) & NAND_STATUS_READY));
return;
/* This applies to read commands */
default:
/*
* If we don't have access to the busy pin, we apply the given
* command delay
*/
if (!this->dev_ready) {
udelay (this->chip_delay);//稍作延迟
return;
}
}
/* Apply this short delay always to ensure that we do wait tWB in
* any case on any machine. */
ndelay (100);
nand_wait_ready(mtd);
}
/*
* Wait for the ready pin, after a command
* The timeout is catched later.
*/
static void nand_wait_ready (struct mtd_info *mtd)
{
struct nand_chip *this = mtd->priv;
unsigned long timeo = jiffies + 2;
/* wait until command is processed or timeout occures */
do {
if (this->dev_ready(mtd)) //简单调用this->dev_ready(s3c2410_nand_devready)函数 等待nand flash become ready
return;
touch_softlockup_watchdog();
} while (time_before(jiffies, timeo));
}
/**
* nand_wait - [DEFAULT] wait until the command is done
* @mtd: MTD device structure
* @this: NAND chip structure
* @state: state to select the max. timeout value
*
* Wait for command done. This applies to erase and program only
* Erase can take up to 400ms and program up to 20ms according to
* general NAND and SmartMedia specs
*
*/
/* 等待知道命令传输完成，适用于檫除和写入命令 */
static int nand_wait (struct mtd_info *mtd, struct nand_chip *this, int state)
{
unsigned long timeo = jiffies;
int status;
if (state == FL_ERASING)
timeo += (HZ * 400) / 1000;//檫除操作的话，时间相对要长一些
else
timeo += (HZ * 20) / 1000;
/* Apply this short delay always to ensure that we do wait tWB in
* any case on any machine. */
ndelay (100);
if ((state == FL_ERASING) && (this->options & NAND_IS_AND))
this->cmdfunc (mtd, NAND_CMD_STATUS_MULTI, -1, -1);
else
this->cmdfunc (mtd, NAND_CMD_STATUS, -1, -1);
while (time_before(jiffies, timeo)) {
/* Check, if we were interrupted */
if (this->state != state)
return 0;
/* 等待nand flash become ready */
if (this->dev_ready) {
if (this->dev_ready(mtd))
break;
} else {
if (this->read_byte(mtd) & NAND_STATUS_READY)
break;
}
cond_resched();
}
status = (int) this->read_byte(mtd);
return status;
}
/**
* nand_block_bad - [DEFAULT] Read bad block marker from the chip
* 检查nand flash中某一页是否为坏块
* @mtd: MTD device structure
* @ofs: offset from device start
* @getchip: 0, if the chip is already selected
*
* Check, if the block is bad.
*/
static int nand_block_bad (struct mtd_info *mtd, loff_t ofs, int getchip)
{
int page, chipnr, res = 0;
struct nand_chip *this = mtd->priv;
u16 bad;
if (getchip) {
page = (int)(ofs >> this->page_shift);
chipnr = (int)(ofs >> this->chip_shift);
/* Grab the lock and see if the device is available */
nand_get_device (this, mtd, FL_READING);
/* Select the NAND device */
this->select_chip(mtd, chipnr);
} else
page = (int) ofs;
if (this->options & NAND_BUSWIDTH_16) {
this->cmdfunc (mtd, NAND_CMD_READOOB, this->badblockpos & 0xFE, page & this->pagemask);
bad = cpu_to_le16(this->read_word(mtd));
if (this->badblockpos & 0x1)
bad >>= 1;
if ((bad & 0xFF) != 0xff)
res = 1;
} else {
this->cmdfunc (mtd, NAND_CMD_READOOB, this->badblockpos, page & this->pagemask);
/* 发送读oob_data命令(oob_data的badblockpos (第6)位记录着坏块标志) */
if (this->read_byte(mtd) != 0xff)//坏块
res = 1;
}
if (getchip) {
/* Deselect and wake up anyone waiting on the device */
nand_release_device(mtd);
}
return res;
}
/**
* nand_default_block_markbad - [DEFAULT] mark a block bad
* 标志坏块
* @mtd: MTD device structure
* @ofs: offset from device start
*
* This is the default implementation, which can be overridden by
* a hardware specific driver.
*/
static int nand_default_block_markbad (struct mtd_info *mtd, loff_t ofs)
{
struct nand_chip *this = mtd->priv;
u_char buf[2] = {0, 0};
size_t retlen;
int block;
/* Get block number */
block = ((int) ofs) >> this->bbt_erase_shift;
if (this->bbt)
this->bbt[block >> 2] |= 0x01 << ((block & 0x03) << 1);
/*
这个暂时不是很好说：内核维护一个标志bad block表，使用2bit来表示1block。
这个表在开机的时候通过扫描nand flash每个block的头两页的oob数据来生成，
发现坏块后至相应的block标志位为非零(有时候至3，但有时候至1，还没搞明白有什么不同)
*/
/* Do we have a flash based bad block table ? */
if (this->options & NAND_USE_FLASH_BBT)//samsun nand flash不属于这种，暂时不去研究，以后同
return nand_update_bbt (mtd, ofs);
/* We write two bytes, so we dont have to mess with 16 bit access */
ofs += mtd->oobsize + (this->badblockpos & ~0x01);//???????????????
return nand_write_oob (mtd, ofs , 2, &retlen, buf);
}
/**
* nand_verify_buf - [DEFAULT] Verify chip data against buffer
* 检验nand flash与buffer的数据是否一致
* @mtd: MTD device structure
* @buf: buffer containing the data to compare
* @len: number of bytes to compare
*
* Default verify function for 8bit buswith
*/
static int nand_verify_buf (struct mtd_info *mtd, const u_char *buf, int len)
{
int i;
struct nand_chip *this = mtd->priv;
for (i=0; i<len; i++)
if (buf[i] != readb(this->IO_ADDR_R))
return -EFAULT;
return 0;
}
/**
* nand_default_bbt - [NAND Interface] Select a default bad block table for the device
* @mtd: MTD device structure
*
* This function selects the default bad block table
* support for the device and calls the nand_scan_bbt function
*
*/
int nand_default_bbt (struct mtd_info *mtd)
{
struct nand_chip *this = mtd->priv;
/* Default for AG-AND. We must use a flash based
* bad block table as the devices have factory marked
* _good_ blocks. Erasing those blocks leads to loss
* of the good / bad information, so we _must_ store
* this information in a good / bad table during
* startup
*/
if (this->options & NAND_IS_AND) {
/* Use the default pattern descriptors */
if (!this->bbt_td) {
this->bbt_td = &bbt_main_descr;
this->bbt_md = &bbt_mirror_descr;
}
this->options |= NAND_USE_FLASH_BBT;
return nand_scan_bbt (mtd, &agand_flashbased);
}
/* Is a flash based bad block table requested ? */
if (this->options & NAND_USE_FLASH_BBT) {
/* Use the default pattern descriptors */
if (!this->bbt_td) {
this->bbt_td = &bbt_main_descr;
this->bbt_md = &bbt_mirror_descr;
}
if (!this->badblock_pattern) {
this->badblock_pattern = (mtd->oobblock > 512) ?
&largepage_flashbased : &smallpage_flashbased;
}
} else { //samsun nand flash的坏块表不存在与nand flash里面，需要扫描来生成。
this->bbt_td = NULL;
this->bbt_md = NULL;
if (!this->badblock_pattern) {
this->badblock_pattern = (mtd->oobblock > 512) ?
&largepage_memorybased : &smallpage_memorybased;
}
}
return nand_scan_bbt (mtd, this->badblock_pattern);
}
/**
* nand_scan_bbt - [NAND Interface] scan, find, read and maybe create bad block table(s)
* @mtd: MTD device structure
* @bd: descriptor for the good/bad block search pattern
*
* The function checks, if a bad block table(s) is/are already
* available. If not it scans the device for manufacturer
* marked good / bad blocks and writes the bad block table(s) to
* the selected place.
*
* The bad block table memory is allocated here. It must be freed
* by calling the nand_free_bbt function.
*
*/
int nand_scan_bbt (struct mtd_info *mtd, struct nand_bbt_descr *bd)
{
struct nand_chip *this = mtd->priv;
int len, res = 0;
uint8_t *buf;
struct nand_bbt_descr *td = this->bbt_td;
struct nand_bbt_descr *md = this->bbt_md;
len = mtd->size >> (this->bbt_erase_shift + 2);
/* Allocate memory (2bit per block) */
/* 2bit per block=(2/8)byte per block，所以上面要多右移2位 */
this->bbt = kmalloc (len, GFP_KERNEL);
if (!this->bbt) {
printk (KERN_ERR "nand_scan_bbt: Out of memory/n");
return -ENOMEM;
}
/* Clear the memory bad block table */
memset (this->bbt, 0x00, len);
/* If no primary table decriptor is given, scan the device
* to build a memory based bad block table
*/
if (!td) {
if ((res = nand_memory_bbt(mtd, bd))) {
printk (KERN_ERR "nand_bbt: Can't scan flash and build the RAM-based BBT/n");
kfree (this->bbt);
this->bbt = NULL;
}
return res;
}
/* Allocate a temporary buffer for one eraseblock incl. oob */
/* 分配1 block所需要的oob data空间 */
len = (1 << this->bbt_erase_shift);
len += (len >> this->page_shift) * mtd->oobsize;
buf = kmalloc (len, GFP_KERNEL);
if (!buf) {
printk (KERN_ERR "nand_bbt: Out of memory/n");
kfree (this->bbt);
this->bbt = NULL;
return -ENOMEM;
}
//由于td、md均为NULL，一下函数基本不起作用，先不去研究它
/* Is the bbt at a given page ? */
if (td->options & NAND_BBT_ABSPAGE) {
res = read_abs_bbts (mtd, buf, td, md);
} else {
/* Search the bad block table using a pattern in oob */
res = search_read_bbts (mtd, buf, td, md);
}
if (res)
res = check_create (mtd, buf, bd);
/* Prevent the bbt regions from erasing / writing */
mark_bbt_region (mtd, td);
if (md)
mark_bbt_region (mtd, md);
kfree (buf);
return res;
}
/**
* nand_memory_bbt - [GENERIC] create a memory based bad block table
* @mtd: MTD device structure
* @bd: descriptor for the good/bad block search pattern
*
* The function creates a memory based bbt by scanning the device
* for manufacturer / software marked good / bad blocks
*/
static inline int nand_memory_bbt (struct mtd_info *mtd, struct nand_bbt_descr *bd)
{
struct nand_chip *this = mtd->priv;
bd->options &= ~NAND_BBT_SCANEMPTY;
//我们只需要扫描oob data，不需要扫描全部(512+16bytes的数据)
return create_bbt (mtd, this->data_buf, bd, -1);
}
/**
* create_bbt - [GENERIC] Create a bad block table by scanning the device
* @mtd: MTD device structure
* @buf: temporary buffer
* @bd: descriptor for the good/bad block search pattern
* @chip: create the table for a specific chip, -1 read all chips.
* Applies only if NAND_BBT_PERCHIP option is set
*
* Create a bad block table by scanning the device
* for the given good/bad block identify pattern
*/
static int create_bbt (struct mtd_info *mtd, uint8_t *buf, struct nand_bbt_descr *bd, int chip)
{
struct nand_chip *this = mtd->priv;
int i, j, numblocks, len, scanlen;
int startblock;
loff_t from;
size_t readlen, ooblen;
printk (KERN_INFO "Scanning device for bad blocks/n");
if (bd->options & NAND_BBT_SCANALLPAGES)//扫描所有都页
len = 1 << (this->bbt_erase_shift - this->page_shift);//求出每block所含的page数
else {
if (bd->options & NAND_BBT_SCAN2NDPAGE)//只检查2 page
len = 2;
else
len = 1;//只检查1 page
}
if (!(bd->options & NAND_BBT_SCANEMPTY)) {
/* We need only read few bytes from the OOB area */
/* 我们只需要检查OOB的某些数据 */
scanlen = ooblen = 0;
readlen = bd->len;
} else {
/* Full page content should be read */
/* 读取整页内容 */
scanlen = mtd->oobblock + mtd->oobsize;
readlen = len * mtd->oobblock;
ooblen = len * mtd->oobsize;
}
if (chip == -1) {
/* Note that numblocks is 2 * (real numblocks) here, see i+=2 below as it
* makes shifting and masking less painful */
/* 计算出nand flash所包含都block数目(注意这里总数目经过林乘2操作)*/
numblocks = mtd->size >> (this->bbt_erase_shift - 1);
startblock = 0;
from = 0;
} else {
if (chip >= this->numchips) {
printk (KERN_WARNING "create_bbt(): chipnr (%d) > available chips (%d)/n",
chip + 1, this->numchips);
return -EINVAL;
}
numblocks = this->chipsize >> (this->bbt_erase_shift - 1);
startblock = chip * numblocks;
numblocks += startblock;
from = startblock << (this->bbt_erase_shift - 1);
}
for (i = startblock; i < numblocks;) {
int ret;
if (bd->options & NAND_BBT_SCANEMPTY) //整页数据读取
if ((ret = nand_read_raw (mtd, buf, from, readlen, ooblen)))
return ret;
for (j = 0; j < len; j++) {
if (!(bd->options & NAND_BBT_SCANEMPTY)) {
size_t retlen;
/* Read the full oob until read_oob is fixed to
* handle single byte reads for 16 bit buswidth */
/* 读取当前页的oob区的所有数据 */
ret = mtd->read_oob(mtd, from + j * mtd->oobblock,
mtd->oobsize, &retlen, buf);
if (ret)
return ret;
/* 检查oob data的bad block标志位，判断是否是坏块 */
if (check_short_pattern (buf, bd)) {
this->bbt[i >> 3] |= 0x03 << (i & 0x6);
/* 注意：这里i=实际值*2。由于一个block的状态用2bit来表示，那么一个字节可以存放4个block的状态。
这里i>>3刚好是实际block/4，4个block的状态刚好存放在this->bbt所指向的一个字节里面
*/
printk (KERN_WARNING "Bad eraseblock %d at 0x%08x/n",
i >> 1, (unsigned int) from);
break;
}
} else {
if (check_pattern (&buf[j * scanlen], scanlen, mtd->oobblock, bd)) {
this->bbt[i >> 3] |= 0x03 << (i & 0x6);
printk (KERN_WARNING "Bad eraseblock %d at 0x%08x/n",
i >> 1, (unsigned int) from);
break;
}
}
}
i += 2;//更新block的序号
from += (1 << this->bbt_erase_shift);//更新nand flash的地址
}
return 0;
}
/**
* nand_release - [NAND Interface] Free resources held by the NAND device
* @mtd: MTD device structure
*/
void nand_release (struct mtd_info *mtd)
{
struct nand_chip *this = mtd->priv;
#ifdef CONFIG_MTD_PARTITIONS
/* Deregister partitions */
del_mtd_partitions (mtd);
#endif
/* Deregister the device */
del_mtd_device (mtd);
/* Free bad block table memory, if allocated */
if (this->bbt)
kfree (this->bbt);
/* Buffer allocated by nand_scan ? */
if (this->options & NAND_OOBBUF_ALLOC)
kfree (this->oob_buf);
/* Buffer allocated by nand_scan ? */
if (this->options & NAND_DATABUF_ALLOC)
kfree (this->data_buf);
}
附录：
/arch/arm/mach-s3c2410/dev.c文件：
static struct mtd_partition partition_info[]={
[0]={
name :"vivi",
size :0x20000,
offset :0,
},[1]={
name :"param",
size :0x10000,
offset :0x20000,
},[2]={
name :"kernel",
size :0x1d0000,
offset :0x30000,
},[3]={
name :"root",
size :0x3c00000,
offset :0x200000,
}
};
struct s3c2410_nand_set nandset={
nr_partitions :4,
partitions :partition_info,
};
struct s3c2410_platform_nand superlpplatform={
tacls :0,
twrph0 :30,
twrph1 :0,
sets :&nandset,
nr_sets :1,
};
struct platform_device s3c_device_nand = {
.name = "s3c2410-nand",
.id = -1,
.num_resources = ARRAY_SIZE(s3c_nand_resource),
.resource = s3c_nand_resource,
.dev={
.platform_data=&superlpplatform
}
};
nand_flash_ids表
/driver/mtd/nand/nand_ids.c文件：
struct nand_flash_dev nand_flash_ids[] = {
................................................................................
{"NAND 64MiB 3,3V 8-bit", 0x76, 512, 64, 0x4000, 0},
................................................................................
};
注：
这里只列出常用的samsun 64M Nand Flash的资料，对应的信息请看该结构体的定义：
struct nand_flash_dev {
char *name;
int id;
unsigned long pagesize;
unsigned long chipsize;
unsigned long erasesize;
unsigned long options;
};
可知该nand flash 设备ID号为0x76，页大小为512，大小为64(M)，檫除单元大小为16(K)。
上一个贴由下到上的介绍了FLASH硬件驱动是如何与MTD原始设备建立联系的，现在再由上到下的研究一下是如何通过MTD原始设备来访问FLASH硬件驱动的。
首先分析一下如何通过MTD原始设备进而通过FLASH硬件驱动来读取FLASH存储器的数据。
引用自<<Linux系统移植>>一文：
"读Nand Flash：
当对nand flash的设备文件(nand flash在/dev下对应的文件)执行系统调用read(),或在某个文件系统中对该
设备进行读操作时. 会调用struct mtd_info中的read方法,他们缺省调用函数为nand_read(),在
drivers/mtd/nand/nand_base.c中定义.nand_read()调用nand_do_read_ecc(),执行读操作. 在
nand_do_read_ecc()函数中,主要完成如下几项工作：
1. 会调用在nand flash驱动中对struct nand_chip重载的select_chip方法,即
s3c2410_nand_select_chip()选择要操作的MTD芯片.
2. 会调用在struct nand_chip中系统缺省的方法cmdfunc发送读命令到nand flash.
3. 会调用在nand flash驱动中对struct nand_chip重载的read_buf(),即s3c2410_nand_read_buf()
从Nand Flash的控制器的数据寄存器中读出数据.
4. 如果有必要的话,会调用在nand flash驱动中对struct nand_chip重载的
enable_hwecc,correct_data以及calculate_ecc方法,进行数据ECC校验。"
下面研究一下其中的细节：
/**
* nand_read - [MTD Interface] MTD compability function for nand_do_read_ecc
* @mtd: MTD device structure
* @from: offset to read from
* @len: number of bytes to read
* @retlen: pointer to variable to store the number of read bytes
* @buf: the databuffer to put data
*
* This function simply calls nand_do_read_ecc with oob buffer and oobsel = NULL
* and flags = 0xff
*/
static int nand_read (struct mtd_info *mtd, loff_t from, size_t len, size_t * retlen, u_char * buf)
{
return nand_do_read_ecc (mtd, from, len, retlen, buf, NULL, &mtd->oobinfo, 0xff);
}
注：
以参数oob_buf为NULL，flags为0xff调用nand_do_read_ecc函数。
/**
* nand_do_read_ecc - [MTD Interface] Read data with ECC
* @mtd: MTD device structure
* @from: offset to read from
* @len: number of bytes to read
* @retlen: pointer to variable to store the number of read bytes
* @buf: the databuffer to put data
* @oob_buf: filesystem supplied oob data buffer (can be NULL)
* @oobsel: oob selection structure
* @flags: flag to indicate if nand_get_device/nand_release_device should be preformed
* and how many corrected error bits are acceptable:
* bits 0..7 - number of tolerable errors
* bit 8 - 0 == do not get/release chip, 1 == get/release chip
*
* NAND read with ECC
*/
int nand_do_read_ecc (struct mtd_info *mtd, loff_t from, size_t len,
size_t * retlen, u_char * buf, u_char * oob_buf,
struct nand_oobinfo *oobsel, int flags)
{
int i, j, col, realpage, page, end, ecc, chipnr, sndcmd = 1;
int read = 0, oob = 0, ecc_status = 0, ecc_failed = 0;
struct nand_chip *this = mtd->priv;
u_char *data_poi, *oob_data = oob_buf;//目前oob_data指针为空，以后会去修改它。
u_char ecc_calc[32];//该数组用于存放计算出来的ecc结果
u_char ecc_code[32];//该数组用于存放oob中ecc部分的数据
int eccmode, eccsteps;//eccmode存放ecc的类型(ECC_SOFT)；
eccsteps用于记录一个page所需的ecc校验次数(2)。
int *oob_config, datidx;
int blockcheck = (1 << (this->phys_erase_shift - this->page_shift)) - 1;
int eccbytes;
int compareecc = 1;//是否需要ecc标志(如果设置成ECC_NONE，这个标志将被清0)
int oobreadlen;
DEBUG (MTD_DEBUG_LEVEL3, "nand_read_ecc: from = 0x%08x, len = %i/n", (unsigned int) from, (int) len);
/* Do not allow reads past end of device */
/* 不允许超越设备容量的读操作 */
if ((from + len) > mtd->size) {
DEBUG (MTD_DEBUG_LEVEL0, "nand_read_ecc: Attempt read beyond end of device/n");
*retlen = 0;
return -EINVAL;
}
/* Grab the lock and see if the device is available */
/* 获取自旋锁，等待设备可用并获取其控制权 */
if (flags & NAND_GET_DEVICE)
nand_get_device (this, mtd, FL_READING);
/* Autoplace of oob data ? Use the default placement scheme */
if (oobsel->useecc == MTD_NANDECC_AUTOPLACE)
oobsel = this->autooob;
/*
* 感觉这一步有点多余，因为nand_scan中已经调用了以下代码：
* memcpy(&mtd->oobinfo, this->autooob, sizeof(mtd->oobinfo));
* 把this->autooob的内容拷贝到mtd->oobinfo中了
*/
eccmode = oobsel->useecc ? this->eccmode : NAND_ECC_NONE;
oob_config = oobsel->eccpos;//记录ecc在oob数据中的位置
/* Select the NAND device */
chipnr = (int)(from >> this->chip_shift);
this->select_chip(mtd, chipnr);//选择nand flash芯片(在s3c2410 nand flash控制器中为空操作)
/* First we calculate the starting page */
/* 首先，我们计算出开始页码 */
realpage = (int) (from >> this->page_shift);
page = realpage & this->pagemask;
/* Get raw starting column */
/* 其次，我们计算页内偏址 */
col = from & (mtd->oobblock - 1);
end = mtd->oobblock;//页大小(512)
ecc = this->eccsize;//ecc保护下的数据大小(256)
eccbytes = this->eccbytes;//ecc所占的字节数(3)
if ((eccmode == NAND_ECC_NONE) || (this->options & NAND_HWECC_SYNDROME))
compareecc = 0;//如果设置为关闭ECC或写操作才需要ECC，那把ecc给禁用(现在可是读操作^_^)
oobreadlen = mtd->oobsize;//16
if (this->options & NAND_HWECC_SYNDROME)
oobreadlen -= oobsel->eccbytes;
/* Loop until all data read */
while (read < len) {
int aligned = (!col && (len - read) >= end);
/*
* If the read is not page aligned, we have to read into data buffer
* due to ecc, else we read into return buffer direct
* 如果要读的位置不是页对齐都话，那么只要先把整页读出来，
* 取出所需要读取的数据，然后修改读位置，那么以后的读操作都是页对齐的了。
*/
if (aligned)
data_poi = &buf[read];
else
data_poi = this->data_buf;
/* Check, if we have this page in the buffer
*
* FIXME: Make it work when we must provide oob data too,
* check the usage of data_buf oob field
* 如果我们所需要的数据还存在于缓冲中都话：
* 1 如果读位置页对齐，我们只要把缓冲中的数据直接拷贝到data_poi(buf[read])中即可(因为数据存在与缓存中，所以也无需要考虑ecc问题)
* 2 如果读位置不是页对齐，什么读不要作，让其继续留在缓存(data_buf)中，以后会从data_poi(指向缓存data_buf)中提取所需要的数据。
*/
if (realpage == this->pagebuf && !oob_buf) {
/* aligned read ? */
if (aligned)
memcpy (data_poi, this->data_buf, end);
goto readdata;
}
/* Check, if we must send the read command */
/* 发送读命令，页地址为page，列地址为0x00 */
if (sndcmd) {
this->cmdfunc (mtd, NAND_CMD_READ0, 0x00, page);
sndcmd = 0;
}
/* get oob area, if we have no oob buffer from fs-driver */
if (!oob_buf || oobsel->useecc == MTD_NANDECC_AUTOPLACE ||
oobsel->useecc == MTD_NANDECC_AUTOPL_USR)
oob_data = &this->data_buf[end];//以上情况，oob_data暂存在data_buf缓存中
eccsteps = this->eccsteps;//2
switch (eccmode) {
case NAND_ECC_NONE: { /* No ECC, Read in a page */
static unsigned long lastwhinge = 0;
if ((lastwhinge / HZ) != (jiffies / HZ)) {
printk (KERN_WARNING "Reading data from NAND FLASH without ECC is not recommended/n");
lastwhinge = jiffies;
}
this->read_buf(mtd, data_poi, end);
break;
}
case NAND_ECC_SOFT: /* Software ECC 3/256: Read in a page + oob data */
this->read_buf(mtd, data_poi, end);//读取数据到data_poi
for (i = 0, datidx = 0; eccsteps; eccsteps--, i+=3, datidx += ecc)
this->calculate_ecc(mtd, &data_poi[datidx], &ecc_calc[i]);
/* 计算出读取到data_poi的数据的ecc值，并存放到ecc_calc数组中。
* 因为读都数据有一页大小(512)，需要分别对其上半部和下半部分计算一次ecc值，并分开存放到ecc_calc数组相应都位置中。
*/
break;
default:
for (i = 0, datidx = 0; eccsteps; eccsteps--, i+=eccbytes, datidx += ecc) {
this->enable_hwecc(mtd, NAND_ECC_READ);
this->read_buf(mtd, &data_poi[datidx], ecc);
/* HW ecc with syndrome calculation must read the
* syndrome from flash immidiately after the data */
if (!compareecc) {
/* Some hw ecc generators need to know when the
* syndrome is read from flash */
this->enable_hwecc(mtd, NAND_ECC_READSYN);
this->read_buf(mtd, &oob_data[i], eccbytes);
/* We calc error correction directly, it checks the hw
* generator for an error, reads back the syndrome and
* does the error correction on the fly */
ecc_status = this->correct_data(mtd, &data_poi[datidx], &oob_data[i], &ecc_code[i]);
if ((ecc_status == -1) || (ecc_status > (flags && 0xff))) {
DEBUG (MTD_DEBUG_LEVEL0, "nand_read_ecc: "
"Failed ECC read, page 0x%08x on chip %d/n", page, chipnr);
ecc_failed++;
}
} else {
this->calculate_ecc(mtd, &data_poi[datidx], &ecc_calc[i]);
}
}
break;
}
/* read oobdata */
this->read_buf(mtd, &oob_data[mtd->oobsize - oobreadlen], oobreadlen);
//读取oob_data存放到oob_data[mtd->oobsize - oobreadlen]，在这里是data_buf[end]中
/* Skip ECC check, if not requested (ECC_NONE or HW_ECC with syndromes) */
/* 跳过ecc检测 */
if (!compareecc)
goto readoob;
/* Pick the ECC bytes out of the oob data */
/* 从刚读出来都oob_data中取出ecc数据(在这里是前三个字节) */
for (j = 0; j < oobsel->eccbytes; j++)
ecc_code[j] = oob_data[oob_config[j]];
/* correct data, if neccecary */
for (i = 0, j = 0, datidx = 0; i < this->eccsteps; i++, datidx += ecc) {
ecc_status = this->correct_data(mtd, &data_poi[datidx], &ecc_code[j], &ecc_calc[j]);
/* 拿前面计算出来都ecc_cal数组都数据与读出来的ecc数据作比较，并尝试修正错误(但不保证能修复，具体看返回值) */
/* Get next chunk of ecc bytes */
j += eccbytes;
/* Check, if we have a fs supplied oob-buffer,
* This is the legacy mode. Used by YAFFS1
* Should go away some day
*/
if (oob_buf && oobsel->useecc == MTD_NANDECC_PLACE) {
int *p = (int *)(&oob_data[mtd->oobsize]);
p[i] = ecc_status;
}
/* 很不幸，ecc检测发现错误且未能修复，报告错误 */
if ((ecc_status == -1) || (ecc_status > (flags && 0xff))) {
DEBUG (MTD_DEBUG_LEVEL0, "nand_read_ecc: " "Failed ECC read, page 0x%08x/n", page);
ecc_failed++;
}
}
readoob:
/* check, if we have a fs supplied oob-buffer */
if (oob_buf) {
/* without autoplace. Legacy mode used by YAFFS1 */
switch(oobsel->useecc) {
case MTD_NANDECC_AUTOPLACE:
case MTD_NANDECC_AUTOPL_USR:
/* Walk through the autoplace chunks */
for (i = 0; oobsel->oobfree[i][1]; i++) {
int from = oobsel->oobfree[i][0];
int num = oobsel->oobfree[i][1];
memcpy(&oob_buf[oob], &oob_data[from], num);
oob += num;
}
break;
case MTD_NANDECC_PLACE:
/* YAFFS1 legacy mode */
oob_data += this->eccsteps * sizeof (int);
default:
oob_data += mtd->oobsize;
}
}
readdata:
/* Partial page read, transfer data into fs buffer
* 读位置不是页对齐，从data_poi(data_buf中)提取所需要都数据
*/
if (!aligned) {
for (j = col; j < end && read < len; j++)
buf[read++] = data_poi[j];//read自增
this->pagebuf = realpage;
} else
read += mtd->oobblock;//整页读取，计数值加上整页的数目(512)
/* Apply delay or wait for ready/busy pin
* Do this before the AUTOINCR check, so no problems
* arise if a chip which does auto increment
* is marked as NOAUTOINCR by the board driver.
*/
if (!this->dev_ready)
udelay (this->chip_delay);
else
nand_wait_ready(mtd);
if (read == len)//所需数据读完都情况，退出读循环 。
break;
/* For subsequent reads align to page boundary. */
col = 0;//对于读位置不是页对齐都情况，前面已对其进行林相应都处理，现在读位置变得页对齐了。
/* Increment page address */
realpage++;//页地址加1,读取下一页。
page = realpage & this->pagemask;
/* Check, if we cross a chip boundary */
if (!page) {
chipnr++;
this->select_chip(mtd, -1);
this->select_chip(mtd, chipnr);
}
/* Check, if the chip supports auto page increment
* or if we have hit a block boundary.
* 如果芯片支持页自增操作,且未到block boundary(15)的话，不用再发送读命令
*/
if (!NAND_CANAUTOINCR(this) || !(page & blockcheck))
sndcmd = 1;
}
/* Deselect and wake up anyone waiting on the device */
if (flags & NAND_GET_DEVICE)
nand_release_device(mtd);//放弃对设备都控制权，好让其它进程获取并占有它
/*
* Return success, if no ECC failures, else -EBADMSG
* fs driver will take care of that, because
* retlen == desired len and result == -EBADMSG
*/
*retlen = read;
return ecc_failed ? -EBADMSG : 0;
}
好的，接着研究一下如何通过MTD原始设备进而通过FLASH硬件驱动向FLASH存储器写数据。
引用自<<Linux系统移植>>一文：
写Nand Flash
当对nand flash的设备文件(nand flash在/dev下对应的文件)执行系统调用write(),或在某个文件系统中对该设备
进行读操作时, 会调用struct mtd_info中write方法,他们缺省调用函数为nand_write(),这两个函数在
drivers/mtd/nand/nand_base.c中定义. nand_write()调用nand_write_ecc(),执行写操作.在
nand_do_write_ecc()函数中,主要完成如下几项工作：
1. 会调用在nand flash驱动中对struct nand_chip重载的select_chip方法,即
s3c2410_nand_select_chip()选择要操作的MTD芯片.
2. 调用nand_write_page()写一个页.
3. 在nand_write_page()中,会调用在struct nand_chip中系统缺省的方法cmdfunc发送写命令
到nand flash.
4. 在nand_write_page()中,会调用在nand flash驱动中对struct nand_chip重载的
write_buf(),即s3c2410_nand_write_buf()从Nand Flash的控制器的数据寄存器中写入数据.
5. 在nand_write_page()中,会调用在nand flash驱动中对struct nand_chip重载waitfunc方法,
该方法调用系统缺省函数nand_wait(),该方法获取操作状态,并等待nand flash操作完成.等
待操作完成,是调用nand flash驱动中对struct nand_chip中重载的dev_ready方法,即
s3c2410_nand_devready()函数.
下面研究一下其中的细节：
/**
* nand_write - [MTD Interface] compability function for nand_write_ecc
* @mtd: MTD device structure
* @to: offset to write to
* @len: number of bytes to write
* @retlen: pointer to variable to store the number of written bytes
* @buf: the data to write
*
* This function simply calls nand_write_ecc with oob buffer and oobsel = NULL
*
*/
static int nand_write (struct mtd_info *mtd, loff_t to, size_t len, size_t * retlen, const u_char * buf)
{
return (nand_write_ecc (mtd, to, len, retlen, buf, NULL, NULL));
}
注：
以参数eccbuf、oobsel为NULL，调用nand_write_ecc函数。
/**
* nand_write_ecc - [MTD Interface] NAND write with ECC
* @mtd: MTD device structure
* @to: offset to write to
* @len: number of bytes to write
* @retlen: pointer to variable to store the number of written bytes
* @buf: the data to write
* @eccbuf: filesystem supplied oob data buffer
* @oobsel: oob selection structure
*
* NAND write with ECC
*/
static int nand_write_ecc (struct mtd_info *mtd, loff_t to, size_t len,
size_t * retlen, const u_char * buf, u_char * eccbuf, struct nand_oobinfo *oobsel)
{
int startpage, page, ret = -EIO, oob = 0, written = 0, chipnr;
int autoplace = 0, numpages, totalpages;
struct nand_chip *this = mtd->priv;
u_char *oobbuf, *bufstart;
int ppblock = (1 << (this->phys_erase_shift - this->page_shift));//page/block
DEBUG (MTD_DEBUG_LEVEL3, "nand_write_ecc: to = 0x%08x, len = %i/n", (unsigned int) to, (int) len);
/* Initialize retlen, in case of early exit */
*retlen = 0;
/* Do not allow write past end of device */
/* 超越nand flash容量的写操作是不允许的 */
if ((to + len) > mtd->size) {
DEBUG (MTD_DEBUG_LEVEL0, "nand_write_ecc: Attempt to write past end of page/n");
return -EINVAL;
}
/* reject writes, which are not page aligned */
/* 不按页对齐的写操作同样是不允许的 */
if (NOTALIGNED (to) || NOTALIGNED(len)) {
printk (KERN_NOTICE "nand_write_ecc: Attempt to write not page aligned data/n");
return -EINVAL;
}
/* Grab the lock and see if the device is available */
/* 获取设备的控制权 */
nand_get_device (this, mtd, FL_WRITING);
/* Calculate chipnr */
/*
* 存在多片flash的情况下，计算出所要写的是哪片flash？
* (当然，像我的板，只用一片nand flash，所以这个操作是不必要的)
*/
chipnr = (int)(to >> this->chip_shift);
/* Select the NAND device */
/* 片选操作 */
this->select_chip(mtd, chipnr);
/* Check, if it is write protected */
/* 如果nand flash写保护，当然不能再写了 */
if (nand_check_wp(mtd))
goto out;
/* if oobsel is NULL, use chip defaults */
if (oobsel == NULL)
oobsel = &mtd->oobinfo;
/* Autoplace of oob data ? Use the default placement scheme */
if (oobsel->useecc == MTD_NANDECC_AUTOPLACE) {
oobsel = this->autooob;
autoplace = 1;
}
if (oobsel->useecc == MTD_NANDECC_AUTOPL_USR)
autoplace = 1;
/* Setup variables and oob buffer */
totalpages = len >> this->page_shift;//计算所要读取的数据长度共有多少页
page = (int) (to >> this->page_shift);//计算数据所要写到的开始页码
/* Invalidate the page cache, if we write to the cached page */
/* 如果缓存保存的数据在我们要写数据的范围内，把缓存里的数据设置为不可用???? */
if (page <= this->pagebuf && this->pagebuf < (page + totalpages))
this->pagebuf = -1;
/* Set it relative to chip */
page &= this->pagemask;
startpage = page;
/* Calc number of pages we can write in one go */
numpages = min (ppblock - (startpage & (ppblock - 1)), totalpages);//计算出本block中允许被写的页数
oobbuf = nand_prepare_oobbuf (mtd, eccbuf, oobsel, autoplace, numpages);//先不深入研究~_~
bufstart = (u_char *)buf;//获取所要写数据的地址
/* Loop until all data is written */
/* 循环进行写操作 */
while (written < len) {
this->data_poi = (u_char*) &buf[written];//先把所要写的数据缓冲到data_poi下
/* Write one page. If this is the last page to write
* or the last page in this block, then use the
* real pageprogram command, else select cached programming
* if supported by the chip.
* 如果这是所写数据的最后一个页或许这是所写block的最后一个页，调用nand flash的
* pageprogram指令，真正把数据写入nand flash中(nand flash的最小擦除单元为block)
*/
ret = nand_write_page (mtd, this, page, &oobbuf[oob], oobsel, (--numpages > 0));
if (ret) {
DEBUG (MTD_DEBUG_LEVEL0, "nand_write_ecc: write_page failed %d/n", ret);
goto out;
}
/* Next oob page */
oob += mtd->oobsize;
/* Update written bytes count */
/* 更新写入计数值 */
written += mtd->oobblock;
if (written == len)//写入完毕，退出
goto cmp;
/* Increment page address */
page++;//下一页
/* Have we hit a block boundary ? Then we have to verify and
* if verify is ok, we have to setup the oob buffer for
* the next pages.
* 暂时不是很明白， 需要先搞明白 nand_prepare_oobbuf函数的作用
*/
if (!(page & (ppblock - 1))){
int ofs;
this->data_poi = bufstart; //怀疑 nand_verify_pages用到
ret = nand_verify_pages (mtd, this, startpage,
page - startpage,
oobbuf, oobsel, chipnr, (eccbuf != NULL));//一页写完，检查数据
if (ret) {
DEBUG (MTD_DEBUG_LEVEL0, "nand_write_ecc: verify_pages failed %d/n", ret);
goto out;
}
*retlen = written;
ofs = autoplace ? mtd->oobavail : mtd->oobsize;
if (eccbuf)
eccbuf += (page - startpage) * ofs;
totalpages -= page - startpage;//更新需要写的页数
numpages = min (totalpages, ppblock);//更新可以写的页数
page &= this->pagemask;//更新页码
startpage = page;//更新开始页码
oobbuf = nand_prepare_oobbuf (mtd, eccbuf, oobsel,
autoplace, numpages);
/* Check, if we cross a chip boundary */
if (!page) {
chipnr++;
this->select_chip(mtd, -1);
this->select_chip(mtd, chipnr);
}
}
}
/* Verify the remaining pages */
cmp:
this->data_poi = bufstart;//怀疑 nand_verify_pages用到
ret = nand_verify_pages (mtd, this, startpage, totalpages,
oobbuf, oobsel, chipnr, (eccbuf != NULL));
if (!ret)
*retlen = written;
else
DEBUG (MTD_DEBUG_LEVEL0, "nand_write_ecc: verify_pages failed %d/n", ret);
out:
/* Deselect and wake up anyone waiting on the device */
nand_release_device(mtd);//放弃对设备的控制权
return ret;
}
/**
* nand_write_page - [GENERIC] write one page
* @mtd: MTD device structure
* @this: NAND chip structure
* @page: startpage inside the chip, must be called with (page & this->pagemask)
* @oob_buf: out of band data buffer
* @oobsel: out of band selecttion structre
* @cached: 1 = enable cached programming if supported by chip
*
* Nand_page_program function is used for write and writev !
* This function will always program a full page of data
* If you call it with a non page aligned buffer, you're lost :)
*
* Cached programming is not supported yet.
*/
static int nand_write_page (struct mtd_info *mtd, struct nand_chip *this, int page,
u_char *oob_buf, struct nand_oobinfo *oobsel, int cached)
{
int i, status;
u_char ecc_code[32];
int eccmode = oobsel->useecc ? this->eccmode : NAND_ECC_NONE;
int *oob_config = oobsel->eccpos;
int datidx = 0, eccidx = 0, eccsteps = this->eccsteps;
int eccbytes = 0;
/* FIXME: Enable cached programming */
cached = 0;//在高版本的内核下找到这样的解释：
/*
* Cached progamming disabled for now, Not sure if its worth the
* trouble. The speed gain is not very impressive. (2.3->2.6Mib/s)
*/
/* Send command to begin auto page programming */
/* 发送页编程指令 */
this->cmdfunc (mtd, NAND_CMD_SEQIN, 0x00, page);
/* Write out complete page of data, take care of eccmode */
switch (eccmode) {
/* No ecc, write all */
case NAND_ECC_NONE:
printk (KERN_WARNING "Writing data without ECC to NAND-FLASH is not recommended/n");
this->write_buf(mtd, this->data_poi, mtd->oobblock);
break;
/* Software ecc 3/256, write all */
case NAND_ECC_SOFT:
for (; eccsteps; eccsteps--) {
this->calculate_ecc(mtd, &this->data_poi[datidx], ecc_code);//计算出一页的ecc数据
for (i = 0; i < 3; i++, eccidx++)
oob_buf[oob_config[eccidx]] = ecc_code[i];//存放到ecc_code数组中
datidx += this->eccsize;
}
this->write_buf(mtd, this->data_poi, mtd->oobblock);//调用FLASH硬件驱动层进行写操作
break;
default:
eccbytes = this->eccbytes;
for (; eccsteps; eccsteps--) {
/* enable hardware ecc logic for write */
this->enable_hwecc(mtd, NAND_ECC_WRITE);
this->write_buf(mtd, &this->data_poi[datidx], this->eccsize);
this->calculate_ecc(mtd, &this->data_poi[datidx], ecc_code);
for (i = 0; i < eccbytes; i++, eccidx++)
oob_buf[oob_config[eccidx]] = ecc_code[i];
/* If the hardware ecc provides syndromes then
* the ecc code must be written immidiately after
* the data bytes (words) */
if (this->options & NAND_HWECC_SYNDROME)
this->write_buf(mtd, ecc_code, eccbytes);
datidx += this->eccsize;
}
break;
}
/* Write out OOB data */
if (this->options & NAND_HWECC_SYNDROME)
this->write_buf(mtd, &oob_buf[oobsel->eccbytes], mtd->oobsize - oobsel->eccbytes);
else
this->write_buf(mtd, oob_buf, mtd->oobsize);//写oob data，主要把上面计算的ecc值写进去
/* Send command to actually program the data */
this->cmdfunc (mtd, cached ? NAND_CMD_CACHEDPROG : NAND_CMD_PAGEPROG, -1, -1);
if (!cached) {
/* call wait ready function */
status = this->waitfunc (mtd, this, FL_WRITING);//等待写入完成
/* See if operation failed and additional status checks are available */
if ((status & NAND_STATUS_FAIL) && (this->errstat)) {
status = this->errstat(mtd, this, FL_WRITING, status, page);
}
/* See if device thinks it succeeded */
if (status & NAND_STATUS_FAIL) {
DEBUG (MTD_DEBUG_LEVEL0, "%s: " "Failed write, page 0x%08x, ", __FUNCTION__, page);
return -EIO;
}
} else {
/* FIXME: Implement cached programming ! */
/* wait until cache is ready*/
// status = this->waitfunc (mtd, this, FL_CACHEDRPG);//cached的写操作暂时没用
}
return 0;
}