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Date:   Mon, 7 May 2018 09:39:33 +0200
From:   Boris Brezillon <boris.brezillon@bootlin.com>
To:     Masahiro Yamada <yamada.masahiro@socionext.com>
Cc:     Abhishek Sahu <absahu@codeaurora.org>,
        Archit Taneja <architt@codeaurora.org>,
        Richard Weinberger <richard@nod.at>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Marek Vasut <marek.vasut@gmail.com>,
        linux-mtd <linux-mtd@lists.infradead.org>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Andy Gross <andy.gross@linaro.org>,
        Brian Norris <computersforpeace@gmail.com>,
        David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH v2 01/14] mtd: rawnand: helper function for setting up
 ECC parameters
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On Mon, 7 May 2018 12:40:39 +0900
Masahiro Yamada <yamada.masahiro@socionext.com> wrote:

> 2018-05-03 21:20 GMT+09:00 Abhishek Sahu <absahu@codeaurora.org>:
> > 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@socionext.com>
> > Signed-off-by: Abhishek Sahu <absahu@codeaurora.org>
> > ---
> > * 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()?

As long as the code does the same thing, I don't care that much.

> 
> My code is simpler,

and I don't see how your code is simpler. Mainly a matter of taste
AFAICS.

> and does not display
> false-positive warning.

I agree on the false-positive warning though, this should be avoided.

> 
> 
> > +       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.

Well, if you have a chip that requires ECC but exposes 0bits/0bytes
then this should be fixed. 0,0 should only be valid when the chip does
not require ECC at all (so, only really old chips). For all other chips,
including non-ONFI ones, we should have a valid value here.

> 
> will be always displayed.
> 
> 
> The strength will be checked by nand_ecc_strength_good() anyway.

True. So, I agree that the pr_warn() is unneeded, but I still think we
should fix all cases where ECC reqs are missing, so if you have such a
setup, please add some code to nand_<vendor>.c to initialize
->ecc_xxx_ds properly.

Thanks,

Boris