分类： LINUX
2009-03-25 17:56:19
Arm-linux东东nand之7: nand_scan_tail
.进入这个函数请大家打十二分精神……因为这个函数会跑MFC那样长的路
………………….
int nand_scan_tail(struct mtd_info *mtd)
{
int i;
struct nand_chip *chip = mtd->priv;
if (!(chip->options & NAND_OWN_BUFFERS))
chip->buffers = kmalloc(sizeof(*chip->buffers), GFP_KERNEL);
if (!chip->buffers)
return -ENOMEM;
/* Set the internal oob buffer location, just after the page data */
chip->oob_poi = chip->buffers->databuf + mtd->writesize;
chip里有个buffers:
struct nand_buffers {
uint8_t ecccalc[NAND_MAX_OOBSIZE];
uint8_t ecccode[NAND_MAX_OOBSIZE];
uint8_t databuf[NAND_MAX_PAGESIZE + NAND_MAX_OOBSIZE];
};
这里oob_poi就是指向databuf的第512个字节.这个地址是放ECC数据的..下面会看到.
……………………
if (!chip->ecc.layout) {
switch (mtd->oobsize) {
case 8:
chip->ecc.layout = &nand_oob_8;
break;
case 16:
chip->ecc.layout = &nand_oob_16;
break;
case 64:
chip->ecc.layout = &nand_oob_64;
break;
default:
printk(KERN_WARNING "No oob scheme defined for "
"oobsize %d\n", mtd->oobsize);
BUG();
}
}
if (!chip->write_page)
chip->write_page = nand_write_page;
/*
* check ECC mode, default to software if 3byte/512byte hardware ECC is
* selected and we have 256 byte pagesize fallback to software ECC
*/
if (!chip->ecc.read_page_raw)
chip->ecc.read_page_raw = nand_read_page_raw;
if (!chip->ecc.write_page_raw)
chip->ecc.write_page_raw=nand_write_page_raw;…………………………………………………………
layout是有值的.接下来就是ecc内的函数指针定值.还是用到再说.
……………………….
switch (chip->ecc.mode) {
case NAND_ECC_HW:
/* Use standard hwecc read page function ? */
if (!chip->ecc.read_page)
chip->ecc.read_page = nand_read_page_hwecc;
if (!chip->ecc.write_page)
chip->ecc.write_page = nand_write_page_hwecc;
if (!chip->ecc.read_oob)
chip->ecc.read_oob = nand_read_oob_std;
if (!chip->ecc.write_oob)
chip->ecc.write_oob = nand_write_oob_std;
case NAND_ECC_HW_SYNDROME:
if ((!chip->ecc.calculate || !chip->ecc.correct ||
!chip->ecc.hwctl) &&
(!chip->ecc.read_page ||
chip->ecc.read_page == nand_read_page_hwecc ||
!chip->ecc.write_page ||
chip->ecc.write_page == nand_write_page_hwecc)) {
printk(KERN_WARNING "No ECC functions supplied, "
"Hardware ECC not possible\n");
BUG();
}
/* Use standard syndrome read/write page function ? */
if (!chip->ecc.read_page)
chip->ecc.read_page = nand_read_page_syndrome;
if (!chip->ecc.write_page)
chip->ecc.write_page = nand_write_page_syndrome;
if (!chip->ecc.read_oob)
chip->ecc.read_oob = nand_read_oob_syndrome;
if (!chip->ecc.write_oob)
chip->ecc.write_oob = nand_write_oob_syndrome;
if (mtd->writesize >= chip->ecc.size)
break;
printk(KERN_WARNING "%d byte HW ECC not possible on "
"%d byte page size, fallback to SW ECC\n",
chip->ecc.size, mtd->writesize);
chip->ecc.mode = NAND_ECC_SOFT;
case NAND_ECC_SOFT:
chip->ecc.calculate = nand_calculate_ecc;
chip->ecc.correct = nand_correct_data;
chip->ecc.read_page = nand_read_page_swecc;
chip->ecc.write_page = nand_write_page_swecc;
chip->ecc.read_oob = nand_read_oob_std;
chip->ecc.write_oob = nand_write_oob_std;
chip->ecc.size = 256;
chip->ecc.bytes = 3;
break;
case NAND_ECC_NONE:
printk(KERN_WARNING "NAND_ECC_NONE selected by board driver. "
"This is not recommended !!\n");
chip->ecc.read_page = nand_read_page_raw;
chip->ecc.write_page = nand_write_page_raw;
chip->ecc.read_oob = nand_read_oob_std;
chip->ecc.write_oob = nand_write_oob_std;
chip->ecc.size = mtd->writesize;
chip->ecc.bytes = 0;
break;
default:
printk(KERN_WARNING "Invalid NAND_ECC_MODE %d\n",
chip->ecc.mode);
BUG();
}
……………………….
ECC又来了.还记得在s3c2410_nand_init_chip中有一句这样的吗:
chip->ecc.mode = NAND_ECC_HW;
这里顺便说下:ECC检验错的问题.如果用硬件算ECC会出错.很多众人就干脆不用.为什么呢.因为bootloader的ECC算法与这里硬件的算法不同.所以就出错.建议在bootloader中的ECC算法改成由硬件来算.
先把下面的说完.等下还会回来的
……………………
chip->ecc.layout->oobavail = 0;
for (i = 0; chip->ecc.layout->oobfree[i].length; i++)
chip->ecc.layout->oobavail +=
chip->ecc.layout->oobfree[i].length;
mtd->oobavail = chip->ecc.layout->oobavail;
/*
* Set the number of read / write steps for one page depending on ECC
* mode
*/
chip->ecc.steps = mtd->writesize / chip->ecc.size;
if(chip->ecc.steps * chip->ecc.size != mtd->writesize) {
printk(KERN_WARNING "Invalid ecc parameters\n");
BUG();
}
chip->ecc.total = chip->ecc.steps * chip->ecc.bytes;
……………………..
Ecc.steps就是算ECC有多少步了.如果ecc.size是256的那么就需要2步.这里的ecc.size是512的所以一步就行了. ecc.total就是所有步下来生成的ecc大小…..
好:来看上面了.对于硬件算ECC来说
if (!chip->ecc.read_page)
chip->ecc.read_page = nand_read_page_hwecc;
if (!chip->ecc.write_page)
chip->ecc.write_page = nand_write_page_hwecc;
if (!chip->ecc.read_oob)
chip->ecc.read_oob = nand_read_oob_std;
if (!chip->ecc.write_oob)
chip->ecc.write_oob = nand_write_oob_std;
这里只说二个函数就是: nand_write_page_hwecc,, nand_read_page_hwecc
…………………………………………………………….
static void nand_write_page_hwecc(struct mtd_info *mtd, struct nand_chip *chip,
const uint8_t *buf)
{
int i, eccsize = chip->ecc.size;
int eccbytes = chip->ecc.bytes;
int eccsteps = chip->ecc.steps;
uint8_t *ecc_calc = chip->buffers->ecccalc;
const uint8_t *p = buf;
uint32_t *eccpos = chip->ecc.layout->eccpos;
for (i = 0; eccsteps; eccsteps--, i += eccbytes, p += eccsize) {
chip->ecc.hwctl(mtd, NAND_ECC_WRITE);
chip->write_buf(mtd, p, eccsize);
chip->ecc.calculate(mtd, p, &ecc_calc[i]);
}
for (i = 0; i < chip->ecc.total; i++)
chip->oob_poi[eccpos[i]] = ecc_calc[i];
chip->write_buf(mtd, chip->oob_poi, mtd->oobsize);
}
……………………………………………………….
有多少步for的循环多少次.我没有骗你吧 . write_buff一次就算一下ECC.
对于nand_read_page_hwecc就比较难了.
……………………………
static int nand_read_page_hwecc(struct mtd_info *mtd, struct nand_chip *chip,
uint8_t *buf)
{
int i, eccsize = chip->ecc.size;
int eccbytes = chip->ecc.bytes;
int eccsteps = chip->ecc.steps;
uint8_t *p = buf;
uint8_t *ecc_calc = chip->buffers->ecccalc;
uint8_t *ecc_code = chip->buffers->ecccode;
uint32_t *eccpos = chip->ecc.layout->eccpos;
for (i = 0; eccsteps; eccsteps--, i += eccbytes, p += eccsize) {
chip->ecc.hwctl(mtd, NAND_ECC_READ);
chip->read_buf(mtd, p, eccsize);
chip->ecc.calculate(mtd, p, &ecc_calc[i]);
}
chip->read_buf(mtd, chip->oob_poi, mtd->oobsize);
for (i = 0; i < chip->ecc.total; i++)
ecc_code[i] = chip->oob_poi[eccpos[i]];
eccsteps = chip->ecc.steps;
p = buf;
…………………………
这里红色的read_buf就是读上面写进去的ECC.放在chip->oob_poi
上面的那个ecc.calculate就是在ECC寄存器的数据.
ecc.layout这里就用到了.拿出对照一下就清楚了.这里就不说了.
………………..
for (i = 0 ; eccsteps; eccsteps--, i += eccbytes, p += eccsize) {
int stat;
stat = chip->ecc.correct(mtd, p, &ecc_code[i], &ecc_calc[i]);
if (stat < 0)
mtd->ecc_stats.failed++;
else
mtd->ecc_stats.corrected += stat;
}
return 0;
…………………..
接下来就要看一下两个ECC的值能不能对的上.
stat = chip->ecc.correct(mtd, p, &ecc_code[i], &ecc_calc[i]);就是调用:
s3c2410_nand_correct_data
static int s3c2410_nand_correct_data(struct mtd_info *mtd, u_char *dat,
u_char *read_ecc, u_char *calc_ecc)
{
struct s3c2410_nand_info *info = s3c2410_nand_mtd_toinfo(mtd);
unsigned int diff0, diff1, diff2;
unsigned int bit, byte;
pr_debug("%s(%p,%p,%p,%p)\n", __func__, mtd, dat, read_ecc, calc_ecc);
diff0 = read_ecc[0] ^ calc_ecc[0];
diff1 = read_ecc[1] ^ calc_ecc[1];
diff2 = read_ecc[2] ^ calc_ecc[2];
pr_debug("%s: rd %02x%02x%02x calc %02x%02x%02x diff %02x%02x%02x\n",
__func__,
read_ecc[0], read_ecc[1], read_ecc[2],
calc_ecc[0], calc_ecc[1], calc_ecc[2],
diff0, diff1, diff2);
if (diff0 == 0 && diff1 == 0 && diff2 == 0)
return 0; /* ECC is ok */
这里diff0 = read_ecc[0] ^ calc_ecc[0];异或是吧.大一的时候老师说了:两个相同的值异或就是0如果read_ecc[0]与calc_ecc[0]相同.那么diff0就是0
if (diff0 == 0 && diff1 == 0 && diff2 == 0)
return 0; /* ECC is ok */
如果个个都为0.那么很好ECC没有问题….
如果不为0呢?接着看:
……………..
if (read_ecc[0] == 0xff && read_ecc[1] == 0xff && read_ecc[2] == 0xff
&& info->platform->ignore_unset_ecc)
return 0;
………………….
为什么是等于0XFF就说明ECC没有问题呢?
在NAND出厂的时候由于没有写过那么所有的内容就是0xFF.如果某个bootleader在写NAND的时候并没有用ECC,那么其内容是不是还是0xFF…OK
……………………
if (((diff0 ^ (diff0 >> 1)) & 0x55) == 0x55 &&
((diff1 ^ (diff1 >> 1)) & 0x55) == 0x55 &&
((diff2 ^ (diff2 >> 1)) & 0x55) == 0x55) {
/* calculate the bit position of the error */
bit = ((diff2 >> 3) & 1) |
((diff2 >> 4) & 2) |
((diff2 >> 5) & 4);
/* calculate the byte position of the error */
byte = ((diff2 << 7) & 0x100) |
((diff1 << 0) & 0x80) |
((diff1 << 1) & 0x40) |
((diff1 << 2) & 0x20) |
((diff1 << 3) & 0x10) |
((diff0 >> 4) & 0x08) |
((diff0 >> 3) & 0x04) |
((diff0 >> 2) & 0x02) |
((diff0 >> 1) & 0x01);
dev_dbg(info->device, "correcting error bit %d, byte %d\n",
bit, byte);
dat[byte] ^= (1 << bit);
return 1;
}
/* if there is only one bit difference in the ECC, then
* one of only a row or column parity has changed, which
* means the error is most probably in the ECC itself */
diff0 |= (diff1 << 8);
diff0 |= (diff2 << 16);
if ((diff0 & ~(1<
return 1;
return -1;
}
…………………………………….
接下来就是有问题的了.但是还能够用ECC把数据恢复过来,谢天谢地.
如果你的程序到了这里,相信这块NAND也不长命的了..
这里的算法不是很懂.所以没有办法说了.
s3c2410_nand_correct_data就完了.一直返回到nand_scan_tail
中来………………..
