On Wed, 16 May 2018 09:32:57 +0200 Chris Moore <[email protected]> wrote:
> Hi, > > Le 15/05/2018 à 09:34, Boris Brezillon a écrit : > > 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. > >> > > 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. Not that much. We just have to allocate srcbufs dynamically and krealloc() everytime we want to add a new entry. May I ask why you care that much about this optimization? As I said, if we really have to read all the copies to realize none of them is good, we already lost a lot of time, so having a "suboptimal but generic" version of the bit-wise majority shouldn't hurt that much.
