Messages in this thread Patch in this message | | | Subject | Re: [PATCH] mtd: fsl_ifc_nand: Recover corrupted empty page for preventing read-only mount in UBIFS | From | Scott Wood <> | Date | Wed, 20 Aug 2014 20:52:52 -0500 |
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On Tue, 2014-04-01 at 01:49 +0000, Eunbong Song wrote: > Even if the meaning of EUCLEAN was changed by commit edbc4540. > There is still possibility of read-only mount in UBIFS with ubifs_scan() "corrupt empty space at LEB". > So i made this patch for fix that problem.
Please elaborate on the nature of the problem.
> This patch do as follow. > - If there are ecc errors which is equal to or less than chip->ecc.strength in page. > - Check that page has how many zero bits, and if zero bits are equal to or less than > chip->ecc.strength then overwrite 1 to zero bits in buf.
This is difficult to parse, with no mention in this sentence that you're talking about corrupted empty pages.
> ubifs_scan() cannot detect corrupted empty space because buf is recovered by this patch. > And this is safe because ecc controller can correct up to chip->ecc.strength bits.
So the concern is that is_blank is failing to report a page that has not been written to but has errors that would have been correctable if the page had been written?
Do most drivers handle this?
> Signed-off-by: Eunbong Song <eunb.song@samsung.com> > --- > drivers/mtd/nand/fsl_ifc_nand.c | 41 +++++++++++++++++++++++++++++++++++++++ > 1 files changed, 41 insertions(+), 0 deletions(-) > > diff --git a/drivers/mtd/nand/fsl_ifc_nand.c b/drivers/mtd/nand/fsl_ifc_nand.c > index 90ca7e7..2129c39 100644 > --- a/drivers/mtd/nand/fsl_ifc_nand.c > +++ b/drivers/mtd/nand/fsl_ifc_nand.c > @@ -277,6 +277,42 @@ static int is_blank(struct mtd_info *mtd, unsigned int bufnum) > return 1; > } > > +static int num_zero_bits(uint8_t val) > +{ > + int i, ret=0; > + > + for(i=7; i>=0 ; i--) > + if(!(0x1 & (val >> i))) > + ret++;
Whitespace (here and elsewhere)
Also, use hweight8(~val) instead of reimplementing it. Or better, use hweight64() and process the data in larger chunks.
> + return ret; > +} > + > +static int is_corrupted_blank(struct mtd_info *mtd, uint8_t * buf) > +{ > + struct nand_chip *chip = mtd->priv; > + int i; > + int zero_bits = 0; > + > + for (i = 0; i < mtd->writesize ; i++) { > + if(buf[i] != 0xff) { > + zero_bits += num_zero_bits(buf[i]); > + } > + } > + > + if(zero_bits && (zero_bits <= chip->ecc.strength)){ > + return 1; > + } > + > + return 0; > +}
What if it's a page that legitimately has only a handful of zero bits? You need to count zero bits in the ECC as well.
Also, this could be combined with is_blank().
> +static void recover_corrupted_blank(struct mtd_info *mtd, uint8_t * buf) > +{ > + memset(buf, 0xff, mtd->writesize); > + return; > +} > + > /* returns nonzero if entire page is blank */ > static int check_read_ecc(struct mtd_info *mtd, struct fsl_ifc_ctrl *ctrl, > u32 *eccstat, unsigned int bufnum) > @@ -760,6 +796,11 @@ static int fsl_ifc_read_page(struct mtd_info *mtd, struct nand_chip *chip, > if (ctrl->nand_stat != IFC_NAND_EVTER_STAT_OPC) > mtd->ecc_stats.failed++; > > + if(nctrl->max_bitflips && (nctrl->max_bitflips <= chip->ecc.strength)){ > + if(is_corrupted_blank(mtd, buf)) > + recover_corrupted_blank(mtd, buf); > + }
If the page is blank except for errors, most likely max_bitflips will be zero because fsl_ifc_run_command() already considered it an uncorrectable error and set ECCER instead. Moving corrupted blank page detection into is_blank() wouldn't have this problem.
How did you test this patch?
-Scott
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