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Subject: Re: [PATCH -next v3 1/2] mtd: nand: toshiba: Retrieve ECC
 requirements from extended ID
From:   KOBAYASHI Yoshitake <yoshitake.kobayashi@toshiba.co.jp>
To:     Boris Brezillon <boris.brezillon@free-electrons.com>
Cc:     richard@nod.at, dwmw2@infradead.org, computersforpeace@gmail.com,
        marek.vasut@gmail.com, cyrille.pitchen@wedev4u.fr,
        linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org
References: <1512569098-30038-1-git-send-email-yoshitake.kobayashi@toshiba.co.jp>
 <1512569098-30038-2-git-send-email-yoshitake.kobayashi@toshiba.co.jp>
 <20171206160805.2435094b@bbrezillon>
 <3e11d966-0801-96f2-8417-194b36a0b775@toshiba.co.jp>
 <20171219125624.58e3e8f8@bbrezillon>
 <b9e62f60-770b-89c3-a2e2-c05767cfd16a@toshiba.co.jp>
Message-ID: <0cf2e0f7-e61b-2cae-f216-e616aecf3e76@toshiba.co.jp>
Date:   Tue, 30 Jan 2018 08:44:30 +0900
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On 2017/12/27 15:06, KOBAYASHI Yoshitake wrote:
> On 2017/12/19 20:56, Boris Brezillon wrote:
>> On Tue, 19 Dec 2017 20:42:36 +0900
>> KOBAYASHI Yoshitake <yoshitake.kobayashi@toshiba.co.jp> wrote:
>>
>>> On 2017/12/07 0:08, Boris Brezillon wrote:
>>>> On Wed,  6 Dec 2017 23:04:57 +0900
>>>> KOBAYASHI Yoshitake <yoshitake.kobayashi@toshiba.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@toshiba.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?
>>>
>>
>> Toshiba NANDs with an id smaller than 6 bytes exist, so no, we should
>> not complain at all. If the controller is broken and can't read the 8 id
>> bytes the core is asking for, then it should be detected at the core
>> level not in the NAND manufacturer driver.
> 
> I understood your opinion. Please apply this patch with dropping the else block.

Should I repost patch with else block dropped? Please let me know if that is necessary.

-- Yoshi