linux-kernel - Re: [PATCH v1] mtd: rawnand: meson: handle OOB buffer according OOB layout

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Message-ID: <98c5a6ef-3865-9254-0af7-2d041a64d368@salutedevices.com>
Date:   Thu, 9 Nov 2023 12:09:34 +0300
From:   Arseniy Krasnov <avkrasnov@...utedevices.com>
To:     Viacheslav Bocharov <adeep@...ina.in>,
        Liang Yang <liang.yang@...ogic.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
CC:     <oxffffaa@...il.com>, <kernel@...rdevices.ru>,
        <linux-mtd@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-amlogic@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] mtd: rawnand: meson: handle OOB buffer according OOB
 layout

Hello, thanks for review!

On 09.11.2023 11:06, Viacheslav Bocharov wrote:
> Hi!
> 
> On Thu, 2023-11-09 at 08:39 +0300, Arseniy Krasnov wrote:
>> In case of MTD_OPS_AUTO_OOB mode, MTD/NAND layer fills/reads OOB buffer
>> according current OOB layout so we need to follow it in the driver.
>>
>> Signed-off-by: Arseniy Krasnov <avkrasnov@...utedevices.com>
>> ---
>>  drivers/mtd/nand/raw/meson_nand.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mtd/nand/raw/meson_nand.c b/drivers/mtd/nand/raw/meson_nand.c
>> index 561d46d860b7..0d4d358152d7 100644
>> --- a/drivers/mtd/nand/raw/meson_nand.c
>> +++ b/drivers/mtd/nand/raw/meson_nand.c
>> @@ -510,7 +510,7 @@ static void meson_nfc_set_user_byte(struct nand_chip *nand, u8 *oob_buf)
>>  	__le64 *info;
>>  	int i, count;
>>  
>> -	for (i = 0, count = 0; i < nand->ecc.steps; i++, count += 2) {
>> +	for (i = 0, count = 0; i < nand->ecc.steps; i++, count += (2 + nand->ecc.bytes)) {
>>  		info = &meson_chip->info_buf[i];
>>  		*info |= oob_buf[count];
>>  		*info |= oob_buf[count + 1] << 8;
> Seems something wrong with your logic here.
> I think this code should most likely look like this:
> 
> for (i = 0, count = 0; i < nand->ecc.steps; i++, count += nand->ecc.bytes) {
>     info = &meson_chip->info_buf[i];
>     *info |= oob_buf[count];
>     if (nand->ecc.bytes > 1)
>       *info |= oob_buf[count + 1] << 8;
> }

For 64 bytes OOB and 512 bytes ECC this driver reports free areas as:

AA AA BB BB BB BB BB BB BB BB BB BB BB BB BB BB
AA AA BB BB BB BB BB BB BB BB BB BB BB BB BB BB
AA AA BB BB BB BB BB BB BB BB BB BB BB BB BB BB
AA AA BB BB BB BB BB BB BB BB BB BB BB BB BB BB

where AA is free byte(user byte), BB - ECC codes. So to access user bytes
we need bytes 0,1,16,17,32,33,48,49. nand->ecc.bytes == 14, so 'count' is
increased at 16 every iteration, so i guess this is correct.

WDYT?

Thanks, Arseniy

> 
> 
>> @@ -523,7 +523,7 @@ static void meson_nfc_get_user_byte(struct nand_chip *nand, u8 *oob_buf)
>>  	__le64 *info;
>>  	int i, count;
>>  
>> -	for (i = 0, count = 0; i < nand->ecc.steps; i++, count += 2) {
>> +	for (i = 0, count = 0; i < nand->ecc.steps; i++, count += (2 + nand->ecc.bytes)) {
>>  		info = &meson_chip->info_buf[i];
>>  		oob_buf[count] = *info;
>>  		oob_buf[count + 1] = *info >> 8;
> And there:
> 
> for (i = 0, count = 0; i < nand->ecc.steps; i++, count += nand->ecc.bytes) {
>     info = &meson_chip->info_buf[i];
>     oob_buf[count] = *info;
>     if (nand->ecc.bytes > 1)
>         oob_buf[count + 1] = *info >> 8;
> }
> 
> 
> This is more similar to the behavior of similar functions in the proprietary U-Boot.
> 
> --
> Viacheslav Bocharov
>