Messages in this thread | | | Date | Thu, 13 Apr 2023 13:32:03 +0800 | Subject | Re: [PATCH v1 4/5] mtd: rawnand: meson: clear OOB buffer before read | From | Liang Yang <> |
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Hi Miquel,
On 2023/4/12 22:32, Miquel Raynal wrote: > [ EXTERNAL EMAIL ] > > Hello, > > liang.yang@amlogic.com wrote on Wed, 12 Apr 2023 22:04:28 +0800: > >> Hi Miquel and Arseniy, >> >> On 2023/4/12 20:57, Miquel Raynal wrote: >>> [ EXTERNAL EMAIL ] >>> >>> Hi Arseniy, >>> >>> avkrasnov@sberdevices.ru wrote on Wed, 12 Apr 2023 15:22:26 +0300: >>> >>>> On 12.04.2023 15:18, Miquel Raynal wrote: >>>>> Hi Arseniy, >>>>> >>>>> avkrasnov@sberdevices.ru wrote on Wed, 12 Apr 2023 13:14:52 +0300: >>>>> >>>> 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)? >>>>> >>>>> Well, you need to cover the same amount of data, yes. But in the ECC >>>>> case the data won't be raw (at least not all of it). >>>> >>>> So "same amount of data", in ECC mode current implementation returns only user OOB bytes (e.g. >>>> OOB data excluding ECC codes), in raw it returns user bytes + ECC codes. IIUC correct >>>> behaviour is to always return user bytes + ECC codes as OOB data even in ECC mode ? >>> >>> If the page are 2k+64B you should read 2k+64B when OOB are requested. >>> >>> If the controller only returns 2k+32B, then perform a random read to >>> just move the read pointer to mtd->size + mtd->oobsize - 32 and >>> retrieve the missing 32 bytes? >> >> 1) raw read can read out the whole page data 2k+64B, decided by the len in the controller raw read command: >> cmd = (len & GENMASK(5, 0)) | scrambler | DMA_DIR(dir); >> after that, the missing oob bytes(not used) can be copied from meson_chip->data_buf. so the implementation of meson_nfc_read_page_raw() is like this if need. >> { >> ...... >> meson_nfc_read_page_sub(nand, page, 1); >> meson_nfc_get_data_oob(nand, buf, oob_buf); >> oob_len = (nand->ecc.bytes + 2) * nand->ecc.steps; >> memcpy(oob_buf + oob_len, meson_chip->data_buf + oob_len, mtd->oobsize - oob_len); >> >> } >> 2) In ECC mode, the controller can't bring back the missing OOB bytes. it can read out the user bytes and ecc bytes per meson_ooblayout_ops define. > > And then (if oob_required) you can bring the missing bytes with > something along: > nand_change_read_column_op(chip, mtd->writesize + oob_len, > oob_buf + oob_len, > mtd->oobsize - oob_len, > false); > Should not be a huge performance hit.
After finishing ECC mode reading, the column address internal in NAND device should be the right pos; it doesn't need to change the column again. so adding controller raw read for the missing bytes after ECC reading may works.
> >> >>> >>> This applies to the two modes, the only difference is: >>> - with correction (commonly named "ECC mode"): the user bytes and ECC >>> bytes should be fixed if there are any bitflips >>> - without correction (commonly referred as "raw mode"): no correction >>> applies, if there are bitflips, give them >>> >>> Please mind the raw mode can be slow, it's meant for debugging and >>> testing, mainly. Page reads however should be fast, so if just moving >>> the column pointer works, then do it, otherwise we'll consider >>> returning FFs. >>> >>> Thanks, >>> Miquèl >>> >> > > > Thanks, > Miquèl >
-- Thanks, Liang
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