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

Abhishek Sahu
2018-05-07T06:02:14Z

On 2018-05-07 09:10, Masahiro Yamada 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()?
>
> 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