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

[Arseniy Krasnov <avkrasnov@sberdevices.ru>]

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

> 
>>
>> 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

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