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

Liang Yang
2023-04-12T10:52:11Z

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@sberdevices.ru wrote on Wed, 12 Apr 2023 12:20:55 +0300:
>>
>>> On 12.04.2023 10:44, Miquel Raynal wrote:
>>>> Hi Arseniy,
>>>>
>>>> AVKrasnov@sberdevices.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@sberdevices.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