linux-kernel - Re: [PATCH v1 4/5] mtd: rawnand: meson: clear OOB buffer before read

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Message-ID: <4baac18b-c223-d346-503c-f5f9ae49320d@amlogic.com>
Date:   Wed, 12 Apr 2023 18:51:18 +0800
From:   Liang Yang <liang.yang@...ogic.com>
To:     Arseniy Krasnov <avkrasnov@...rdevices.ru>,
        Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Jianxin Pan <jianxin.pan@...ogic.com>,
        Yixun Lan <yixun.lan@...ogic.com>, oxffffaa@...il.com,
        kernel@...rdevices.ru, linux-mtd@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 4/5] mtd: rawnand: meson: clear OOB buffer before read

Hi Arseniy and Miquel,

On 2023/4/12 18:14, Arseniy Krasnov wrote:
> [ EXTERNAL EMAIL ]
> 
> 
> 
> On 12.04.2023 12:36, Miquel Raynal wrote:
>> Hi Arseniy,
>>
>> avkrasnov@...rdevices.ru wrote on Wed, 12 Apr 2023 12:20:55 +0300:
>>
>>> On 12.04.2023 10:44, Miquel Raynal wrote:
>>>> Hi Arseniy,
>>>>
>>>> AVKrasnov@...rdevices.ru wrote on Wed, 12 Apr 2023 09:16:58 +0300:
>>>>    
>>>>> This NAND reads only few user's bytes in ECC mode (not full OOB), so
>>>>
>>>> "This NAND reads" does not look right, do you mean "Subpage reads do
>>>> not retrieve all the OOB bytes,"?
>>>>    
>>>>> fill OOB buffer with zeroes to not return garbage from previous reads
>>>>> to user.
>>>>> Otherwise 'nanddump' utility prints something like this for just erased
>>>>> page:
>>>>>
>>>>> ...
>>>>> 0x000007f0: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>>>>>    OOB Data: ff ff ff ff 00 00 ff ff 80 cf 22 99 cb ad d3 be
>>>>>    OOB Data: 63 27 ae 06 16 0a 2f eb bb dd 46 74 41 8e 88 6e
>>>>>    OOB Data: 38 a1 2d e6 77 d4 05 06 f2 a5 7e 25 eb 34 7c ff
>>>>>    OOB Data: 38 ea de 14 10 de 9b 40 33 16 6a cc 9d aa 2f 5e
>>>>>
>>>>> Signed-off-by: Arseniy Krasnov <AVKrasnov@...rdevices.ru>
>>>>> ---
>>>>>   drivers/mtd/nand/raw/meson_nand.c | 5 +++++
>>>>>   1 file changed, 5 insertions(+)
>>>>>
>>>>> diff --git a/drivers/mtd/nand/raw/meson_nand.c b/drivers/mtd/nand/raw/meson_nand.c
>>>>> index f84a10238e4d..f2f2472cb511 100644
>>>>> --- a/drivers/mtd/nand/raw/meson_nand.c
>>>>> +++ b/drivers/mtd/nand/raw/meson_nand.c
>>>>> @@ -858,9 +858,12 @@ static int meson_nfc_read_page_sub(struct nand_chip *nand,
>>>>>   static int meson_nfc_read_page_raw(struct nand_chip *nand, u8 *buf,
>>>>>   				   int oob_required, int page)
>>>>>   {
>>>>> +	struct mtd_info *mtd = nand_to_mtd(nand);
>>>>>   	u8 *oob_buf = nand->oob_poi;
>>>>>   	int ret;
>>>>>   
>>>>> +	memset(oob_buf, 0, mtd->oobsize);
>>>>
>>>> I'm surprised raw reads do not read the entire OOB?
>>>
>>> Yes! Seems in case of raw access (what i see in this driver) number of OOB bytes read
>>> still depends on ECC parameters: for each portion of data covered with ECC code we can
>>> read it's ECC code and "user bytes" from OOB - it is what i see by dumping DMA buffer by
>>> printk(). For example I'm working with 2K NAND pages, each page has 2 x 1K ECC blocks.
>>> For each ECC block I have 16 OOB bytes which I can access by read/write. Each 16 bytes
>>> contains 2 bytes of user's data and 14 bytes ECC codes. So when I read page in raw mode
>>> controller returns 32 bytes (2 x (2 + 14)) of OOB. While OOB is reported as 64 bytes.
>>
>> In all modes, when you read OOB, you should get the full OOB. The fact
>> that ECC correction is enabled or disabled does not matter. If the NAND
>> features OOB sections of 64 bytes, you should get the 64 bytes.
>>
>> What happens sometimes, is that some of the bytes are not protected
>> against bitflips, but the policy is to return the full buffer.
> 
> Ok, so to clarify case for this NAND controller:
> 1) In both ECC and raw modes i need to return the same raw OOB data (e.g. user bytes
>     + ECC codes)?
> 2) If I have access to only 32 bytes of OOB (in case above), I must report that size
>     of OOB is only 32 bytes during initialization?
> 
> Thanks, Arseniy

Yes. it should return all the OOB data. i make a mistake on raw read and 
there is wrong code in meson_nfc_read_page_raw().
	meson_nfc_get_data_oob(nand, buf, oob_buf);
changed to:
	if (oob_required)
		memcpy(oob_buf, buf + mtd->writesize, mtd->oobsize)

for the ECC mode, i define the meson_ooblayout_ops in host driver.

> 
>>
>>>
>>> Thanks, Arseniy
>>>
>>>>    
>>>>> +
>>>>>   	ret = meson_nfc_read_page_sub(nand, page, 1);
>>>>>   	if (ret)
>>>>>   		return ret;
>>>>> @@ -881,6 +884,8 @@ static int meson_nfc_read_page_hwecc(struct nand_chip *nand, u8 *buf,
>>>>>   	u8 *oob_buf = nand->oob_poi;
>>>>>   	int ret, i;
>>>>>   
>>>>> +	memset(oob_buf, 0, mtd->oobsize);
>>>>> +
>>>>>   	ret = meson_nfc_read_page_sub(nand, page, 0);
>>>>>   	if (ret)
>>>>>   		return ret;
>>>>
>>>>
>>>> Thanks,
>>>> Miquèl
>>
>>
>> Thanks,
>> Miquèl
> 

-- 
Thanks,
Liang