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SubjectRe: [PATCH v3 01/16] mtd: rawnand: helper function for setting up ECC configuration
On Sat, 26 May 2018 10:42:47 +0200
Miquel Raynal <miquel.raynal@bootlin.com> wrote:

> Hi Abhishek,
>
> On Fri, 25 May 2018 17:51:29 +0530, Abhishek Sahu
> <absahu@codeaurora.org> wrote:
>
> > commit 2c8f8afa7f92 ("mtd: nand: add generic helpers to check,
> > match, maximize ECC settings") provides generic helpers which
> > drivers can use for setting up ECC parameters.
> >
> > Since same board can have different ECC strength nand chips so
> > following is the logic for setting up ECC strength and ECC step
> > size, which can be used by most of the drivers.
> >
> > 1. If both ECC step size and ECC strength are already set
> > (usually by DT) then just check whether this setting
> > is supported by NAND controller.
> > 2. If NAND_ECC_MAXIMIZE is set, then select maximum ECC strength
> > supported by NAND controller.
> > 3. Otherwise, try to match the ECC step size and ECC strength closest
> > to the chip's requirement. If available OOB size can't fit the chip
> > requirement then select maximum ECC strength which can be fit with
> > available OOB size.
> >
> > This patch introduces nand_ecc_choose_conf function which calls the
> > required helper functions for the above logic. The drivers can use
> > this single function instead of calling the 3 helper functions
> > individually.
> >
> > CC: Masahiro Yamada <yamada.masahiro@socionext.com>
> > Signed-off-by: Abhishek Sahu <absahu@codeaurora.org>
> > ---
> > * Changes from v2:
> >
> > 1. Renamed function to nand_ecc_choose_conf.
> > 2. Minor code reorganization to remove warning and 2 function calls
> > for nand_maximize_ecc.
> >
> > * Changes from v1:
> > NEW PATCH
> >
> > drivers/mtd/nand/raw/nand_base.c | 42 ++++++++++++++++++++++++++++++++++++++++
> > drivers/mtd/nand/raw/nand_base.c | 31 +++++++++++++++++++++++++++++++
> > include/linux/mtd/rawnand.h | 3 +++
> > 2 files changed, 34 insertions(+)
> >
> > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> > index 72f3a89..e52019d 100644
> > --- a/drivers/mtd/nand/raw/nand_base.c
> > +++ b/drivers/mtd/nand/raw/nand_base.c
> > @@ -6249,6 +6249,37 @@ int nand_maximize_ecc(struct nand_chip *chip,
> > }
> > EXPORT_SYMBOL_GPL(nand_maximize_ecc);
> >
> > +/**
> > + * nand_ecc_choose_conf - Set the ECC strength and ECC step size
> > + * @chip: nand chip info structure
> > + * @caps: ECC engine caps info structure
> > + * @oobavail: OOB size that the ECC engine can use
> > + *
> > + * Choose the ECC configuration according to following logic
> > + *
> > + * 1. If both ECC step size and ECC strength are already set (usually by DT)
> > + * then check if it is supported by this controller.
> > + * 2. If NAND_ECC_MAXIMIZE is set, then select maximum ECC strength.
> > + * 3. Otherwise, try to match the ECC step size and ECC strength closest
> > + * to the chip's requirement. If available OOB size can't fit the chip
> > + * requirement then fallback to the maximum ECC step size and ECC strength.
> > + *
> > + * On success, the chosen ECC settings are set.
> > + */
> > +int nand_ecc_choose_conf(struct nand_chip *chip,
> > + const struct nand_ecc_caps *caps, int oobavail)
> > +{
> > + if (chip->ecc.size && chip->ecc.strength)
> > + return nand_check_ecc_caps(chip, caps, oobavail);
> > +
> > + if (!(chip->ecc.options & NAND_ECC_MAXIMIZE) &&
> > + !nand_match_ecc_req(chip, caps, oobavail))
> > + return 0;
> > +
> > + return nand_maximize_ecc(chip, caps, oobavail);
>
> I personally don't mind if nand_maximize_ecc() is called twice in
> the function if it clarifies the logic. Maybe the following will be
> more clear for the user?
>
> if (chip->ecc.size && chip->ecc.strength)
> return nand_check_ecc_caps(chip, caps, oobavail);
>
> if (chip->ecc.options & NAND_ECC_MAXIMIZE)
> return nand_maximize_ecc(chip, caps, oobavail);
>
> if (!nand_match_ecc_req(chip, caps, oobavail))
> return 0;
>
> return nand_maximize_ecc(chip, caps, oobavail);

I personally don't mind, and it seems Masahiro wanted to keep the logic
he had used in the denali driver.

>
> Also, I'm not sure we should just error out when nand_check_ecc_caps()
> fails. What about something more robust, like:
>
> int ret;
>
> if (chip->ecc.size && chip->ecc.strength) {
> ret = nand_check_ecc_caps(chip, caps, oobavail);
> if (ret)
> goto maximize_ecc;

Nope. When someone asked for a specific ECC config by passing the
nand-ecc-xxx props we should apply it or return an erro if it's not
supported. People passing those props should now what the ECC engine
supports and pick one valid values.

>
> return 0;
> }
>
> if (chip->ecc.options & NAND_ECC_MAXIMIZE)
> goto maximize_ecc;
>
> ret = nand_match_ecc_req(chip, caps, oobavail);
> if (ret)
> goto maximize_ecc;
>
> return 0;
>
> maximize_ecc:
> return nand_maximize_ecc(chip, caps, oobavail);
>

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