Messages in this thread | | | Subject | Re: [PATCH v7] mtd: rawnand: use bit-wise majority to recover the contents of ONFI parameter | From | Chris Moore <> | Date | Wed, 16 May 2018 09:32:57 +0200 |
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Hi,
Le 15/05/2018 à 09:34, Boris Brezillon a écrit : > On Tue, 15 May 2018 06:45:51 +0200 > Chris Moore <moore@free.fr> 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 <Jane.Wan@nokia.com> >>> --- >>> 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. >>
I do understand that the ONFI specifications permit more than 3 copies. However elsewhere the proposed code shows no intention of handling other cases. The constant 3 is hard coded in the following lines extracted from the proposed code: ... + p = kzalloc((sizeof(*p) * 3), GFP_KERNEL); ... for (i = 0; i < 3; i++) { ... if (i == 3) { ... + const void *srcbufs[3] = {p, p + 1, p + 2};
Moreover the last of these is difficult to generalize.
Cheers, Chris
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