linux-kernel - Re: [PATCH v3 2/2] mtd: rawnand: brcmnand: improve hamming oob layout

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Message-Id: <461FD58F-ACD5-4158-BC0B-8C73C53D5C0D@gmail.com>
Date:   Tue, 12 May 2020 09:26:23 +0200
From:   Álvaro Fernández Rojas <noltari@...il.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     computersforpeace@...il.com, kdasu.kdev@...il.com, richard@....at,
        vigneshr@...com, sumit.semwal@...aro.org,
        linux-mtd@...ts.infradead.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v3 2/2] mtd: rawnand: brcmnand: improve hamming oob layout

Hi Miquèl,

> El 12 may 2020, a las 9:19, Miquel Raynal <miquel.raynal@...tlin.com> escribió:
> 
> Hi Álvaro,
> 
> Álvaro Fernández Rojas <noltari@...il.com> wrote on Tue, 12 May 2020
> 09:12:10 +0200:
> 
>> Hi Miquel,
>> 
>> I also had a hard time understanding your email.
>> It was quite misleading.
>> 
>>> El 12 may 2020, a las 9:08, Miquel Raynal <miquel.raynal@...tlin.com> escribió:
>>> 
>>> Hi Álvaro,
>>> 
>>> Álvaro Fernández Rojas <noltari@...il.com> wrote on Tue, 12 May 2020
>>> 08:00:23 +0200:
>>> 
>>>> The current code generates 8 oob sections:
>>>> S1	1-5
>>>> ECC	6-8
>>>> S2	9-15
>>>> S3	16-21
>>>> ECC	22-24
>>>> S4	25-31
>>>> S5	32-37
>>>> ECC	38-40
>>>> S6	41-47
>>>> S7	48-53
>>>> ECC	54-56
>>>> S8	57-63
>>>> 
>>>> Change it by merging continuous sections:
>>>> S1	1-5
>>>> ECC	6-8
>>>> S2	9-21
>>>> ECC	22-24
>>>> S3	25-37
>>>> ECC	38-40
>>>> S4	41-53
>>>> ECC	54-56
>>>> S5	57-63
>>>> 
>>>> Fixes: ef5eeea6e911 ("mtd: nand: brcm: switch to mtd_ooblayout_ops")  
>>> 
>>> Sorry for leading you the wrong way, actually this patch does not
>>> deserve a Fixes tag.  
>> 
>> Do I need to resend this again?
>> Looks like no matter what I do it’s always wrong...
> 
> Please don't give up! It is normal to work back and forth with the
> community. I need the patch to be clear and bug-free so I ask you to
> make changes and ask questions, that's how it works. But all your
> patches are enhancing this driver so please keep posting!
> 
>> 
>>> 
>>>> Signed-off-by: Álvaro Fernández Rojas <noltari@...il.com>
>>>> ---
>>>> v3: invert patch order
>>>> v2: keep original comment and fix correctly skip byte 6 for small-page nand
>>>> 
>>>> drivers/mtd/nand/raw/brcmnand/brcmnand.c | 37 ++++++++++++------------
>>>> 1 file changed, 18 insertions(+), 19 deletions(-)
>>>> 
>>>> diff --git a/drivers/mtd/nand/raw/brcmnand/brcmnand.c b/drivers/mtd/nand/raw/brcmnand/brcmnand.c
>>>> index 1c1070111ebc..0a1d76fde37b 100644
>>>> --- a/drivers/mtd/nand/raw/brcmnand/brcmnand.c
>>>> +++ b/drivers/mtd/nand/raw/brcmnand/brcmnand.c
>>>> @@ -1100,33 +1100,32 @@ static int brcmnand_hamming_ooblayout_free(struct mtd_info *mtd, int section,
>>>> 	struct brcmnand_cfg *cfg = &host->hwcfg;
>>>> 	int sas = cfg->spare_area_size << cfg->sector_size_1k;
>>>> 	int sectors = cfg->page_size / (512 << cfg->sector_size_1k);
>>>> +	u32 next;
>>>> 
>>>> -	if (section >= sectors * 2)
>>>> +	if (section > sectors)
>>>> 		return -ERANGE;
>>>> 
>>>> -	oobregion->offset = (section / 2) * sas;
>>>> +	next = (section * sas);
>>>> +	if (section < sectors)
>>>> +		next += 6;
>>>> 
>>>> -	if (section & 1) {
>>>> -		oobregion->offset += 9;
>>>> -		oobregion->length = 7;
>>>> +	if (section) {
>>>> +		oobregion->offset = ((section - 1) * sas) + 9;
>>>> 	} else {
>>>> -		oobregion->length = 6;
>>>> -
>>>> -		/* First sector of each page may have BBI */
>>>> -		if (!section) {
>>>> -			/*
>>>> -			 * Small-page NAND use byte 6 for BBI while large-page
>>>> -			 * NAND use bytes 0 and 1.
>>>> -			 */
>>>> -			if (cfg->page_size > 512) {
>>>> -				oobregion->offset += 2;
>>>> -				oobregion->length -= 2;
>>>> -			} else {
>>>> -				oobregion->length--;
>>>> -			}
>>>> +		/*
>>>> +		 * Small-page NAND use byte 6 for BBI while large-page
>>>> +		 * NAND use bytes 0 and 1.
>>>> +		 */
>>>> +		if (cfg->page_size > 512) {
>>>> +			oobregion->offset = 2;
>>>> +		} else {
>>>> +			oobregion->offset = 0;
>>>> +			next--;  
>>> 
>>> This next-- seems very strange, can you explain?  
>> 
>> In this case next will be 6 (which is the first ECC byte).
>> However, for small page NANDs byte 5 is reserved for BBT, so we want next to be 5 only in this case.
> 
> That's clear, please add a comment there then.

Isn’t “Small-page NAND use byte 6 for BBI while large-page NAND use bytes 0 and 1.” enough?
Do we really need a specific comment before next--?

> 
>> 
>>> 
>>>> 		}
>>>> 	}
>>>> 
>>>> +	oobregion->length = next - oobregion->offset;
>>>> +
>>>> 	return 0;
>>>> }
>>>> 
>>> 
>>> 
>>> Thanks,
>>> Miquèl  
>> 
>> Regards,
>> Álvaro.
> 
> 
> 
> Thanks,
> Miquèl

Regards,
Álvaro.