On Tue, 15 May 2018 06:45:51 +0200 Chris Moore <[email protected]> wrote:
> Hi, > > Le 13/05/2018 à 06:30, Wan, Jane (Nokia - US/Sunnyvale) a écrit : > > Per ONFI specification (Rev. 4.0), if all parameter pages have invalid CRC > > values, the bit-wise majority may be used to recover the contents of the > > parameter pages from the parameter page copies present. > > > > Signed-off-by: Jane Wan <[email protected]> > > --- > > v7: change debug print messages > > v6: support the cases that srcbufs are not contiguous > > v5: make the bit-wise majority functon generic > > v4: move the bit-wise majority code in a separate function > > v3: fix warning message detected by kbuild test robot > > v2: rebase the changes on top of v4.17-rc1 > > > > drivers/mtd/nand/raw/nand_base.c | 50 > > ++++++++++++++++++++++++++++++++++---- > > 1 file changed, 45 insertions(+), 5 deletions(-) > > > > diff --git a/drivers/mtd/nand/raw/nand_base.c > > b/drivers/mtd/nand/raw/nand_base.c > > index 72f3a89..b43b784 100644 > > --- a/drivers/mtd/nand/raw/nand_base.c > > +++ b/drivers/mtd/nand/raw/nand_base.c > > @@ -5087,6 +5087,35 @@ static int nand_flash_detect_ext_param_page(struct > > nand_chip *chip, > > } > > > > /* > > + * Recover data with bit-wise majority > > + */ > > +static void nand_bit_wise_majority(const void **srcbufs, > > + unsigned int nsrcbufs, > > + void *dstbuf, > > + unsigned int bufsize) > > +{ > > + int i, j, k; > > + > > + for (i = 0; i < bufsize; i++) { > > + u8 cnt, val; > > + > > + val = 0; > > + for (j = 0; j < 8; j++) { > > + cnt = 0; > > + for (k = 0; k < nsrcbufs; k++) { > > + const u8 *srcbuf = srcbufs[k]; > > + > > + if (srcbuf[i] & BIT(j)) > > + cnt++; > > + } > > + if (cnt > nsrcbufs / 2) > > + val |= BIT(j); > > + } > > + ((u8 *)dstbuf)[i] = val; > > + } > > +} > > + > > +/* > > * Check if the NAND chip is ONFI compliant, returns 1 if it is, 0 > > otherwise. > > */ > > static int nand_flash_detect_onfi(struct nand_chip *chip) > > @@ -5102,7 +5131,7 @@ static int nand_flash_detect_onfi(struct nand_chip > > *chip) > > return 0; > > > > /* ONFI chip: allocate a buffer to hold its parameter page */ > > - p = kzalloc(sizeof(*p), GFP_KERNEL); > > + p = kzalloc((sizeof(*p) * 3), GFP_KERNEL); > > if (!p) > > return -ENOMEM; > > > > @@ -5113,21 +5142,32 @@ static int nand_flash_detect_onfi(struct nand_chip > > *chip) > > } > > > > for (i = 0; i < 3; i++) { > > - ret = nand_read_data_op(chip, p, sizeof(*p), true); > > + ret = nand_read_data_op(chip, &p[i], sizeof(*p), true); > > if (ret) { > > ret = 0; > > goto free_onfi_param_page; > > } > > > > - if (onfi_crc16(ONFI_CRC_BASE, (uint8_t *)p, 254) == > > + if (onfi_crc16(ONFI_CRC_BASE, (u8 *)&p[i], 254) == > > le16_to_cpu(p->crc)) { > > + if (i) > > + memcpy(p, &p[i], sizeof(*p)); > > break; > > } > > } > > > > if (i == 3) { > > - pr_err("Could not find valid ONFI parameter page; aborting\n"); > > - goto free_onfi_param_page; > > + const void *srcbufs[3] = {p, p + 1, p + 2}; > > + > > + pr_warn("Could not find a valid ONFI parameter page, trying > > bit-wise majority to recover it\n"); > > + nand_bit_wise_majority(srcbufs, ARRAY_SIZE(srcbufs), p, > > + sizeof(*p)); > > + > > + if (onfi_crc16(ONFI_CRC_BASE, (u8 *)p, 254) != > > + le16_to_cpu(p->crc)) { > > + pr_err("ONFI parameter recovery failed, aborting\n"); > > + goto free_onfi_param_page; > > + } > > } > > > > /* Check version */ > > This version is still hard coded for a three sample bitwise majority vote. > So why not use the method which I suggested previously for v2 and which > I repeat below? Because I want the nand_bit_wise_majority() function to work with nsrcbufs > 3 (the ONFI spec says there's at least 3 copy of the param page, but NAND vendor can decide to put more). Also, if the X copies of the PARAM are corrupted (which is rather unlikely), that means we already spent quite a lot of time reading the different copies and calculating the CRC, so I think we don't care about perf optimizations when doing bit-wise majority. > > The three sample bitwise majority can be implemented without bit level > manipulation using the identity: > majority3(a, b, c) = (a & b) | (a & c) | (b & c) > This can be factorized slightly to (a & (b | c)) | (b & c) > This enables the operation to be performed 8, 16, 32 or even 64 bits at > a time depending on the hardware. > > This method is not only faster and but also more compact. > > Cheers, > Chris > > > ______________________________________________________ > Linux MTD discussion mailing list > http://lists.infradead.org/mailman/listinfo/linux-mtd/
