linux-kernel - Re: [PATCH v3] mtd: rawnand: brcmnand: correctly verify erased pages

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Date:   Tue, 12 May 2020 09:16:37 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Álvaro Fernández Rojas <noltari@...il.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] mtd: rawnand: brcmnand: correctly verify erased
 pages

Hi Álvaro,

Álvaro Fernández Rojas <noltari@...il.com> wrote on Tue, 12 May 2020
08:51:11 +0200:

> The current code checks that the whole OOB area is erased.
> This is a problem when JFFS2 cleanmarkers are added to the OOB, since it will
> fail due to the usable OOB bytes not being 0xff.
> Correct this by only checking that data and ECC bytes aren't 0xff.
> 
> Fixes: 02b88eea9f9c ("mtd: brcmnand: Add check for erased page bitflips")
> Signed-off-by: Álvaro Fernández Rojas <noltari@...il.com>
> ---
>  v3: Fix commit log and merge nand_check_erased_ecc_chunk calls.
>  v2: Add Fixes tag
> 
>  drivers/mtd/nand/raw/brcmnand/brcmnand.c | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/brcmnand/brcmnand.c b/drivers/mtd/nand/raw/brcmnand/brcmnand.c
> index e4e3ceeac38f..80fe01f03516 100644
> --- a/drivers/mtd/nand/raw/brcmnand/brcmnand.c
> +++ b/drivers/mtd/nand/raw/brcmnand/brcmnand.c
> @@ -2018,8 +2018,9 @@ static int brcmnand_read_by_pio(struct mtd_info *mtd, struct nand_chip *chip,
>  static int brcmstb_nand_verify_erased_page(struct mtd_info *mtd,
>  		  struct nand_chip *chip, void *buf, u64 addr)
>  {
> +	struct mtd_oob_region oobecc;
>  	int i, sas;
> -	void *oob = chip->oob_poi;
> +	void *oob;
>  	int bitflips = 0;
>  	int page = addr >> chip->page_shift;
>  	int ret;
> @@ -2035,11 +2036,19 @@ static int brcmstb_nand_verify_erased_page(struct mtd_info *mtd,
>  	if (ret)
>  		return ret;
>  
> -	for (i = 0; i < chip->ecc.steps; i++, oob += sas) {
> +	for (i = 0; i < chip->ecc.steps; i++) {
>  		ecc_chunk = buf + chip->ecc.size * i;
> -		ret = nand_check_erased_ecc_chunk(ecc_chunk,
> -						  chip->ecc.size,
> -						  oob, sas, NULL, 0,
> +
> +		if (mtd->ooblayout->ecc(mtd, i, &oobecc)) {

Please use the mtdcore.c's helpers
(mtd_ooblayout_set/get_data/free/ecc/bytes).

Also, what are you trying to discriminate with the return code of the
function? Shouldn't this function "always" work?

> +			oob = NULL;
> +			oobecc.length = 0;
> +		} else {
> +			oob = chip->oob_poi + oobecc.offset;
> +		}
> +
> +		ret = nand_check_erased_ecc_chunk(ecc_chunk, chip->ecc.size,
> +						  oob, oobecc.length,
> +						  NULL, 0,
>  						  chip->ecc.strength);

As I told you, this helper takes "maid data" then "spare area" then
"ecc bytes". The names are pretty important here as you want to avoid
checking the spare OOB bytes on purpose, so maybe you could have more
meaningful names and call "ecc" instead of "oob" the ecc region?
 
>  		if (ret < 0)
>  			return ret;


Thanks,
Miquèl