Re: [PATCH v2 01/14] mtd: rawnand: helper function for setting up ECC parameters

[Abhishek Sahu]

On 2018-05-07 09:10, Masahiro Yamada wrote:
> 2018-05-03 21:20 GMT+09:00 Abhishek Sahu <absahu@xxxxxxxxxxxxxx>:
> > 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 with warning.
> >
> > This patch introduces nand_ecc_param_setup 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@xxxxxxxxxxxxx>
> > Signed-off-by: Abhishek Sahu <absahu@xxxxxxxxxxxxxx>
> > ---
> > * Changes from v1:
> >
> >   NEW PATCH
> >
> >  drivers/mtd/nand/raw/nand_base.c | 42 
> > ++++++++++++++++++++++++++++++++++++++++
> >  include/linux/mtd/rawnand.h      |  3 +++
> >  2 files changed, 45 insertions(+)
> >
> > diff --git a/drivers/mtd/nand/raw/nand_base.c 
> > b/drivers/mtd/nand/raw/nand_base.c
> > index 72f3a89..dd7a984 100644
> > --- a/drivers/mtd/nand/raw/nand_base.c
> > +++ b/drivers/mtd/nand/raw/nand_base.c
> > @@ -6249,6 +6249,48 @@ int nand_maximize_ecc(struct nand_chip *chip,
> >  }
> >  EXPORT_SYMBOL_GPL(nand_maximize_ecc);
> >
> > +/**
> > + * nand_ecc_param_setup - 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 strength 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
> > + *    and print the warning.
> > + *
> > + * On success, the chosen ECC settings are set.
> > + */
> > +int nand_ecc_param_setup(struct nand_chip *chip,
> > +                        const struct nand_ecc_caps *caps, int 
> > oobavail)
> > +{
> > +       int ret;
> > +
> > +       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;
> > +
> > +       ret = nand_maximize_ecc(chip, caps, oobavail);
>
>
> Why two calls for nand_maximize_ecc()?
>
> My code is simpler, and does not display
> false-positive warning.

 Thanks Masahiro.

 Since, Now this is in moved to generic layer that's why I put
 this warning that this function is falling back to some
 other ECC settings which is not recommend by chip.

 If this warning seems unnecessary then I can remove this
 and then directly your code changes can be put here
 instead of calling nand_maximize_ecc 2 times.

> > +       if (!ret)
> > +               pr_warn("ECC (step, strength) = (%d, %d) not supported 
> > on this controller. Fallback to (%d, %d)\n",
> > +                       chip->ecc_step_ds, chip->ecc_strength_ds,
> > +                       chip->ecc.size, chip->ecc.strength);
>
>
> This is annoying.
>
> {ecc_step_ds, ecc_strength_ds} are not provided by Non-ONFi devices.
>
> So,
>   ECC (step, strength) = (0, 0) not supported on this controller.
>
> will be always displayed.
>
>
> The strength will be checked by nand_ecc_strength_good() anyway.

 But for most of the non ONFI devices also, this is being calculated
 by ID.

 You can get some background for this in
 http://lists.infradead.org/pipermail/linux-mtd/2018-April/080193.html

 Regards,
 Abhishek