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Date:   Thu, 13 Apr 2023 10:22:53 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     Liang Yang <liang.yang@amlogic.com>
Cc:     Arseniy Krasnov <avkrasnov@sberdevices.ru>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Kevin Hilman <khilman@baylibre.com>,
        Jerome Brunet <jbrunet@baylibre.com>,
        Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
        Jianxin Pan <jianxin.pan@amlogic.com>,
        Yixun Lan <yixun.lan@amlogic.com>, oxffffaa@gmail.com,
        kernel@sberdevices.ru, linux-mtd@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org,
        linux-amlogic@lists.infradead.org, linux-kernel@vger.kernel.org,
        "yonghui.yu" <yonghui.yu@amlogic.com>
Subject: Re: [PATCH v1 4/5] mtd: rawnand: meson: clear OOB buffer before
 read
Message-ID: <20230413102253.2ee6bae4@xps-13>
In-Reply-To: <0c61eaae-053e-5768-a533-70b2ff0cc95d@amlogic.com>
References: <20230412061700.1492474-1-AVKrasnov@sberdevices.ru>
        <20230412061700.1492474-5-AVKrasnov@sberdevices.ru>
        <20230412094400.3c82f631@xps-13>
        <ac4b66da-6a76-c2ec-7e21-31632f3448d5@sberdevices.ru>
        <20230412113654.183350d0@xps-13>
        <4eace0a0-f6af-7d99-a52f-7913a2139330@sberdevices.ru>
        <20230412141824.755b2bca@xps-13>
        <eedaaed9-0a41-2c18-9eb2-792613566986@sberdevices.ru>
        <20230412145715.58c2be4a@xps-13>
        <7c996832-258f-001c-56bd-87bbdf23eeaa@amlogic.com>
        <20230412163214.0c764bb3@xps-13>
        <0c61eaae-053e-5768-a533-70b2ff0cc95d@amlogic.com>
Organization: Bootlin
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Hi Liang,

liang.yang@amlogic.com wrote on Thu, 13 Apr 2023 13:32:03 +0800:

> Hi Miquel,
>=20
> On 2023/4/12 22:32, Miquel Raynal wrote:
> > [ EXTERNAL EMAIL ]
> >=20
> > Hello,
> >=20
> > liang.yang@amlogic.com wrote on Wed, 12 Apr 2023 22:04:28 +0800:
> >  =20
> >> Hi Miquel and Arseniy,
> >>
> >> On 2023/4/12 20:57, Miquel Raynal wrote: =20
> >>> [ EXTERNAL EMAIL ]
> >>>
> >>> Hi Arseniy,
> >>>
> >>> avkrasnov@sberdevices.ru wrote on Wed, 12 Apr 2023 15:22:26 +0300: =20
> >>>    >>>> On 12.04.2023 15:18, Miquel Raynal wrote: =20
> >>>>> Hi Arseniy,
> >>>>>
> >>>>> avkrasnov@sberdevices.ru wrote on Wed, 12 Apr 2023 13:14:52 +0300: =
=20
> >>>>>     >>>> On 12.04.2023 12:36, Miquel Raynal wrote: =20
> >>>>>>> Hi Arseniy,
> >>>>>>>
> >>>>>>> avkrasnov@sberdevices.ru wrote on Wed, 12 Apr 2023 12:20:55 +0300=
: =20
> >>>>>>>       >>>>>> On 12.04.2023 10:44, Miquel Raynal wrote: =20
> >>>>>>>>> Hi Arseniy,
> >>>>>>>>>
> >>>>>>>>> AVKrasnov@sberdevices.ru wrote on Wed, 12 Apr 2023 09:16:58 +03=
00: =20
> >>>>>>>>>         >>>>>>>> This NAND reads only few user's bytes in ECC m=
ode (not full OOB), so =20
> >>>>>>>>>
> >>>>>>>>> "This NAND reads" does not look right, do you mean "Subpage rea=
ds do
> >>>>>>>>> not retrieve all the OOB bytes,"? =20
> >>>>>>>>>         >>>>>>>> fill OOB buffer with zeroes to not return garb=
age from previous reads =20
> >>>>>>>>>> to user.
> >>>>>>>>>> Otherwise 'nanddump' utility prints something like this for ju=
st 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/n=
and/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 =3D nand_to_mtd(nand);
> >>>>>>>>>>    	u8 *oob_buf =3D nand->oob_poi;
> >>>>>>>>>>    	int ret; =20
> >>>>>>>>>>    >>>>>>>> +	memset(oob_buf, 0, mtd->oobsize); =20
> >>>>>>>>>
> >>>>>>>>> I'm surprised raw reads do not read the entire OOB? =20
> >>>>>>>>
> >>>>>>>> Yes! Seems in case of raw access (what i see in this driver) num=
ber of OOB bytes read
> >>>>>>>> still depends on ECC parameters: for each portion of data covere=
d 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 rea=
d/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. =20
> >>>>>>>
> >>>>>>> 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 th=
e NAND
> >>>>>>> features OOB sections of 64 bytes, you should get the 64 bytes.
> >>>>>>>
> >>>>>>> What happens sometimes, is that some of the bytes are not protect=
ed
> >>>>>>> against bitflips, but the policy is to return the full buffer. =20
> >>>>>>
> >>>>>> Ok, so to clarify case for this NAND controller:
> >>>>>> 1) In both ECC and raw modes i need to return the same raw OOB dat=
a (e.g. user bytes
> >>>>>>      + ECC codes)? =20
> >>>>>
> >>>>> 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). =20
> >>>>
> >>>> 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 co=
des. IIUC correct
> >>>> behaviour is to always return user bytes + ECC codes as OOB data eve=
n in ECC mode ? =20
> >>>
> >>> 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? =20
> >>
> >> 1) raw read can read out the whole page data 2k+64B, decided by the le=
n in the controller raw read command:
> >> 	cmd =3D (len & GENMASK(5, 0)) | scrambler | DMA_DIR(dir);
> >> after that, the missing oob bytes(not used) can be copied from meson_c=
hip->data_buf. so the implementation of meson_nfc_read_page_raw() is like t=
his if need.
> >> 	{
> >> 		......
> >> 		meson_nfc_read_page_sub(nand, page, 1);
> >> 		meson_nfc_get_data_oob(nand, buf, oob_buf);
> >> 		oob_len =3D (nand->ecc.bytes + 2) * nand->ecc.steps;
> >> 		memcpy(oob_buf + oob_len, meson_chip->data_buf + oob_len, mtd->oobsi=
ze - 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 defin=
e. =20
> >=20
> > 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. =20
>=20
> After finishing ECC mode reading, the column address internal in NAND dev=
ice 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 wor=
ks.

Yes, if the last byte read is the one right before the "missing" bytes,
then that will work.

Thanks,
Miqu=C3=A8l