Hi,

On Mon, Feb 01, 2021 at 03:18:24PM +0100, Miquel Raynal wrote:

Hi Manivannan,

Manivannan Sadhasivam [off-list ref] wrote on Sat,
30 Jan 2021 09:24:12 +0530:

quoted

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.

quoted

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?

The issue I encountered is, on the Telit FN980 device one of the
partition seems to be protected. So trying to read the bad blocks in
that partition makes the device to reboot during boot.

There seems to be no flag passed by the parser for this partition. So
the only way I could let the device to boot is to completely skip the
bad block check.

AFAIK, MTD core only supports checking for the reserved blocks to be
used for BBM and there is no way to check for a reserved partition like
this.

I agree that skipping bad block check is not a sane way but I don't know
any other way to handle this problem.

Thanks,
Mani

quoted

Signed-off-by: Manivannan Sadhasivam <redacted>
---
 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