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

[Arseniy Krasnov]

On 12.04.2023 10:44, Miquel Raynal wrote:
> Hi Arseniy,
> 
> AVKrasnov@xxxxxxxxxxxxxx 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@xxxxxxxxxxxxxx>
>> ---
>>  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.

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