linux-kernel - Re: [PATCH -next v3 1/2] mtd: nand: toshiba: Retrieve ECC requirements from extended ID

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Message-ID: <3e11d966-0801-96f2-8417-194b36a0b775@toshiba.co.jp>
Date:   Tue, 19 Dec 2017 20:42:36 +0900
From:   KOBAYASHI Yoshitake <yoshitake.kobayashi@...hiba.co.jp>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     richard@....at, dwmw2@...radead.org, computersforpeace@...il.com,
        marek.vasut@...il.com, cyrille.pitchen@...ev4u.fr,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next v3 1/2] mtd: nand: toshiba: Retrieve ECC
 requirements from extended ID

On 2017/12/07 0:08, Boris Brezillon wrote:
> On Wed,  6 Dec 2017 23:04:57 +0900
> KOBAYASHI Yoshitake <yoshitake.kobayashi@...hiba.co.jp> wrote:
> 
>> This patch enables support to read the ECC strength and size from the
>> NAND flash using Toshiba Memory SLC NAND extended-ID. This patch is
>> based on the information of the 6th ID byte of the Toshiba Memory SLC
>> NAND.
>>
>> Signed-off-by: KOBAYASHI Yoshitake <yoshitake.kobayashi@...hiba.co.jp>
>> ---
>>  drivers/mtd/nand/nand_toshiba.c | 28 ++++++++++++++++++++++++++++
>>  1 file changed, 28 insertions(+)
>>
>> diff --git a/drivers/mtd/nand/nand_toshiba.c b/drivers/mtd/nand/nand_toshiba.c
>> index 57df857..c2c141b 100644
>> --- a/drivers/mtd/nand/nand_toshiba.c
>> +++ b/drivers/mtd/nand/nand_toshiba.c
>> @@ -35,6 +35,34 @@ static void toshiba_nand_decode_id(struct nand_chip *chip)
>>  	    (chip->id.data[5] & 0x7) == 0x6 /* 24nm */ &&
>>  	    !(chip->id.data[4] & 0x80) /* !BENAND */)
>>  		mtd->oobsize = 32 * mtd->writesize >> 9;
>> +
>> +	/*
>> +	 * Extract ECC requirements from 6th id byte.
>> +	 * For Toshiba SLC, ecc requrements are as follows:
>> +	 *  - 43nm: 1 bit ECC for each 512Byte is required.
>> +	 *  - 32nm: 4 bit ECC for each 512Byte is required.
>> +	 *  - 24nm: 8 bit ECC for each 512Byte is required.
>> +	 */
>> +	if (chip->id.len >= 6 && nand_is_slc(chip)) {
>> +		chip->ecc_step_ds = 512;
>> +		switch (chip->id.data[5] & 0x7) {
>> +		case 0x4:
>> +			chip->ecc_strength_ds = 1;
>> +			break;
>> +		case 0x5:
>> +			chip->ecc_strength_ds = 4;
>> +			break;
>> +		case 0x6:
>> +			chip->ecc_strength_ds = 8;
>> +			break;
>> +		default:
>> +			WARN(1, "Could not get ECC info");
>> +			chip->ecc_step_ds = 0;
>> +			break;
>> +		}
>> +	} else if (chip->id.len < 6 && nand_is_slc(chip)) {
>> +		WARN(1, "Could not get ECC info, 6th nand id byte does not exist.");
> 
> I'm pretty sure you have old NAND chips that do not have 6bytes ids
> (see the table here [1]), and printing a huge backtrace in this case is
> probably not what you want.
> 
> If you're okay with dropping this else block, I'll do the change when
> applying, no need to send a new version.

Some controllers may have limitation in reading ids beyond 5 bytes, 
considering such scenario we think it is better to keep this warning.
However if you feel huge backtrace is an issue, how about we using pr_warn() instead?