linux-kernel - Re: [PATCH] mtd: rawnand: Do not check for bad block if bbt is unavailable

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Date:   Mon, 1 Feb 2021 15:18:24 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     richard@....at, vigneshr@...com, boris.brezillon@...labora.com,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, bjorn.andersson@...aro.org
Subject: Re: [PATCH] mtd: rawnand: Do not check for bad block if bbt is
 unavailable

Hi Manivannan,

Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org> wrote on Sat,
30 Jan 2021 09:24:12 +0530:

> The bbt pointer will be unavailable when NAND_SKIP_BBTSCAN option is
> set for a NAND chip. The intention is to skip scanning for the bad
> blocks during boot time.

I don't have the same understanding: this flag skips the bad block
table scan, not the bad block scan. We do want to scan all the devices
in order to construct a RAM based table.

> However, the MTD core will call
> _block_isreserved() and _block_isbad() callbacks unconditionally for
> the rawnand devices due to the callbacks always present while collecting
> the ecc stats.
> 
> The _block_isreserved() callback for rawnand will bail out if bbt
> pointer is not available. But _block_isbad() will continue without
> checking for it. So this contradicts with the NAND_SKIP_BBTSCAN option
> since the bad block check will happen anyways (ie., not much difference
> between scanning for bad blocks and checking each block for bad ones).
> 
> Hence, do not check for the bad block if bbt pointer is unavailable.

Not checking for bad blocks at all feels insane. I don't really get the
scope and goal of such change?

> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
>  drivers/mtd/nand/raw/nand_base.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> index c33fa1b1847f..f18cd1db79a9 100644
> --- a/drivers/mtd/nand/raw/nand_base.c
> +++ b/drivers/mtd/nand/raw/nand_base.c
> @@ -4286,6 +4286,9 @@ static int nand_block_isbad(struct mtd_info *mtd, loff_t offs)
>  	int chipnr = (int)(offs >> chip->chip_shift);
>  	int ret;
>  
> +	if (!chip->bbt)
> +		return 0;
> +
>  	/* Select the NAND device */
>  	ret = nand_get_device(chip);
>  	if (ret)

Cheers,
Miquèl