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Date:   Tue, 08 May 2018 12:51:07 +0530
From:   Abhishek Sahu <absahu@codeaurora.org>
To:     Masahiro Yamada <yamada.masahiro@socionext.com>
Cc:     Boris Brezillon <boris.brezillon@bootlin.com>,
        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 2018-05-08 11:44, Masahiro Yamada wrote:
> 2018-05-07 16:39 GMT+09:00 Boris Brezillon 
> <boris.brezillon@bootlin.com>:
>> 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.
> 
> 
> Sorry, it was my misunderstanding.
> 
> My NAND chip is Toshiba.
> 
> If I remember correctly, Toshiba chips were not set
> with ECC requirements in the past,
> but as far as I tested the latest kernel now,
> the ECC requirement was set by
> drivers/mtd/nand/raw/nand_toshiba.c
> 
> 
> 
> 
> 
>>> 
>>> 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.
>> 
> 
> If we decide to not display pr_warn(),
> I think the code like denali_ecc_setup() should work, and simple.

  Thanks Boris and Masahiro.
  I will remove this print and then we can use code like 
denali_ecc_setup.

  Regards,
  Abhishek