Messages in this thread | | | Subject | Re: [PATCH v2 2/2] mtd: rawnand: fsl_ifc: use bit-wise majority to | From | Chris Moore <> | Date | Fri, 11 May 2018 07:03:31 +0200 |
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Hi,
Le 04/05/2018 à 04:09, Wan, Jane (Nokia - US/Sunnyvale) a écrit > The following is the reposting of patch with v2 version indication based on comment on "[PATCH 1/2]" (also in the attachment). > > Subject: [PATCH v2 2/2] mtd: rawnand: fsl_ifc: use bit-wise majority to > recover the contents of ONFI parameter > > 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> > --- > drivers/mtd/nand/raw/nand_base.c | 36 ++++++++++++++++++++++++++++++------ > 1 file changed, 30 insertions(+), 6 deletions(-) > > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c > index 72f3a89..464c4fb 100644 > --- a/drivers/mtd/nand/raw/nand_base.c > +++ b/drivers/mtd/nand/raw/nand_base.c
[snip]
> > + pr_info("Recover ONFI params with bit-wise majority\n"); > + for (j = 0; j < pagesize; j++) { > + v = 0; > + for (k = 0; k < 8; k++) { > + m = 0; > + for (l = 0; l < 3; l++) > + m += GET_BIT(k, buf[l*pagesize + j]); > + if (m > 1) > + v |= BIT(k); > + } > + ((u8 *)p)[j] = v; > + }
I am not familiar with the context of this but the three way bit-wise majority can be implemented much more efficiently 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.
Cheers, Chris
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