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Date:   Sat, 13 Jun 2020 11:16:28 -0400
From:   Kamal Dasu <kdasu.kdev@...il.com>
To:     Álvaro Fernández Rojas <noltari@...il.com>
Cc:     Brian Norris <computersforpeace@...il.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        "R, Vignesh" <vigneshr@...com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        MTD Maling List <linux-mtd@...ts.infradead.org>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH] mtd: rawnand: brcmnand: force raw OOB writes

Alvaro,


On Sat, Jun 13, 2020 at 5:01 AM Álvaro Fernández Rojas
<noltari@...il.com> wrote:
>
> Hi Kamal,
>
> > El 12 jun 2020, a las 20:47, Kamal Dasu <kdasu.kdev@...il.com> escribió:
> >
> > On Fri, Jun 5, 2020 at 1:07 PM Álvaro Fernández Rojas <noltari@...il.com> wrote:
> >>
> >> MTD_OPS_AUTO_OOB is writting OOB with ECC enabled, which changes all ECC bytes
> >> from an erased page to 0x00 when JFFS2 cleanmarkers are added with mtd-utils.
> >>         | BBI |   JFFS2   |   ECC   |   JFFS2   | Spare  |
> >> 00000800  ff ff 19 85 20 03 00 00  00 00 00 00 08 ff ff ff
> >>
> >> However, if OOB is written with ECC disabled, the JFFS2 cleanmarkers are
> >> correctly written without changing the ECC bytes:
> >>         | BBI |   JFFS2   |   ECC   |   JFFS2   | Spare  |
> >> 00000800  ff ff 19 85 20 03 ff ff  ff 00 00 00 08 ff ff ff
> >
> > Both brcmand_write_oob_raw() and brcmnand_write_oob() use
> > brcmnand_write() that uses PROGRAM_PAGE cmd, means also programs data
> > areas and ECC when enabled  is always calculated on DATA+OOB.  since
>
> Are you sure about that? I think that HW ECC is only calculated for DATA, not for OOB.
> The fact that we’re not writing any DATA seems to be the problem that is changing all ECC bytes to 0x00.
>

Only true for 1-bit hamming code on early controller versions.  For
BCH algorithms both data+oob are covered. And the controller driver
intentionally does not implement a spare area program cmd, even for
OOB writes. Also BRCMNAND_ACC_CONTROL_PARTIAL_PAGE=0 (when present)
does not allow for spare areas only writes.

> > in both cases we only want to modify OOB, data is always assumed to be
> > 0xffs (means erased state). So as far as this api always is used on
> > the erased page it should be good. Are the sub-pages/oob areas read by
> > jffs2  also read without ecc enabled?. Just want to be sure that it
> > does not break any other utilities like nandwrite.
>
> No, sub-pages/oob areas read by JFFS2 with ECC enabled.
> I don’t think this breaks anything at all, since I tested nandwrite with OOB enabled and everything was written perfectly.
>

Going by the commit message you are assuming 1-bit hamming  code, that
is the only exception on early version controllers where only data was
covered for ecc calculations when enabled.
Which version of the controller are you using  ?. Did you test with
BCH-4 or any BCH ?.

> BTW, I tried another approach that forced MTD_OPS_AUTO_OOB to be written as raw OOB, but it was rejected:
> http://patchwork.ozlabs.org/project/linux-mtd/patch/20200504094253.2741109-1-noltari@gmail.com/
> https://lkml.org/lkml/2020/5/4/215
>

Are there any other use cases other than jffs2 where only oob needs to
be modified ?. But surely intentionally disabling ecc instead of
forcing it is the way, but I am not sure it will still work for other
BCH algorithms though where both data and oob are covered.

> >
> >>
> >> Signed-off-by: Álvaro Fernández Rojas <noltari@...il.com>
> >> ---
> >> drivers/mtd/nand/raw/brcmnand/brcmnand.c | 9 +--------
> >> 1 file changed, 1 insertion(+), 8 deletions(-)
> >>
> >> diff --git a/drivers/mtd/nand/raw/brcmnand/brcmnand.c b/drivers/mtd/nand/raw/brcmnand/brcmnand.c
> >> index 8f9ffb46a09f..566281770841 100644
> >> --- a/drivers/mtd/nand/raw/brcmnand/brcmnand.c
> >> +++ b/drivers/mtd/nand/raw/brcmnand/brcmnand.c
> >> @@ -2279,13 +2279,6 @@ static int brcmnand_write_page_raw(struct nand_chip *chip, const uint8_t *buf,
> >>        return nand_prog_page_end_op(chip);
> >> }
> >>
> >> -static int brcmnand_write_oob(struct nand_chip *chip, int page)
> >> -{
> >> -       return brcmnand_write(nand_to_mtd(chip), chip,
> >> -                             (u64)page << chip->page_shift, NULL,
> >> -                             chip->oob_poi);
> >> -}
> >> -
> >> static int brcmnand_write_oob_raw(struct nand_chip *chip, int page)
> >> {
> >>        struct mtd_info *mtd = nand_to_mtd(chip);
> >> @@ -2642,7 +2635,7 @@ static int brcmnand_init_cs(struct brcmnand_host *host, struct device_node *dn)
> >>        chip->ecc.write_oob_raw = brcmnand_write_oob_raw;
> >>        chip->ecc.read_oob_raw = brcmnand_read_oob_raw;
> >>        chip->ecc.read_oob = brcmnand_read_oob;
> >> -       chip->ecc.write_oob = brcmnand_write_oob;
> >> +       chip->ecc.write_oob = brcmnand_write_oob_raw;
> >>
> >>        chip->controller = &ctrl->controller;
> >>
> >> --
> >> 2.26.2
> >>
>
> Best regards,
> Álvaro.

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