Re: imx27: No space left to write bad block table

Guillaume Tucker
2021-04-21T20:46:24Z

On 20/04/2021 07:26, Stefan Riedmüller wrote:
> Hi Miquel,
>
> On Mon, 2021-04-19 at 17:36 +0200, Miquel Raynal wrote:
>> Hi Stefan,
>>
>>>> Interesting. Maybe I overlooked the below commit when applying. Indeed,
>>>> BBT may be considered as bad blocks, so I wonder if the below change is
>>>> valid now...
>>>>
>>>> Guillaume, would you have a way to revert this patch on top of
>>>> linux-next? Stefan, would you mind giving more details on the testing
>>>> procedure?

Sorry I'm late to the party, was busy with some other kernelci
issues. I gather this is being reverted anyway now, but please
let me know if you still need to check anything. As far as I can
tell, there hasn't been any automated bisection landing on this
commit.

It's generally possible to re-run anything, i.e. make a kernel
build with a custom patchset and run one given test on any of the
platforms in KernelCI. There just isn't any public self-service
for doing that (yet).

Best wishes,
Guillaume

>>> I have tested this on an i.MX 6 by simulating two bad BBT blocks by simply
>>> returning -EIO in nand_erase_nand when the block to be erased is one of
>>> the
>>> first two BBT blocks.
>>>
>>> I have seen this once on a customer board but were not able to reproduce
>>> it
>>> anymore, thus the simulation of the two bad blocks.
>>>
>>> Without the patch below new versions of the BBT can no longer be written
>>> to
>>> the first two blocks reserved for the BBT but they are still evaluated to
>>> read
>>> the BBT from during boot due the lack of a test if these blocks are bad.
>>> So
>>> changes to the BBT after these two blocks turn bad are only kept and used
>>> until the next reboot where again the old version of the two worn blocks
>>> is
>>> used as a basis.
>>>
>>> I tried to use the same mechanism that is used to identify bad blocks
>>> during a
>>> scan for bad blocks. But maybe I missed something there? Or were my
>>> assumptions wrong in the first place?
>>
>> Honestly I don't know what is wrong exactly in this patch.
>>
>> We will revert the commit as it clearly breaks something fundamental
>> and the merge window is too close to adopt a hackish attitude.
>>
>> I would propose the following tests with your board:
>> - Hack the core to allow yourself to access bad blocks from userspace
>> for testing purposes.
>> - With the below commit, you should have the same behavior than
>> reported by Fabio.
>> - Revert the commit.
>> - Manually change the bad block markers (nanddump, flash_erase,
>> nandwrite) to declare the two tables bad. Reboot and observe if there
>> are any issues. You can try to work from there.
>
> Thanks for the input! I will follow your suggestions and let you guys know my
> findings.
>
> Regards,
> Stefan
>
>>
>>>> ---8<---
>>>>
>>>> commit bd9c9fe2ad04546940f4a9979d679e62cae6aa51
>>>> Author: Stefan Riedmueller <s.riedmueller@phytec.de>
>>>> Date: Thu Mar 25 11:23:37 2021 +0100
>>>>
>>>> mtd: rawnand: bbt: Skip bad blocks when searching for the BBT in
>>>> NAND
>>>>
>>>> The blocks containing the bad block table can become bad as well. So
>>>> make sure to skip any blocks that are marked bad when searching for
>>>> the
>>>> bad block table.
>>>>
>>>> Otherwise in very rare cases where two BBT blocks wear out it might
>>>> happen that an obsolete BBT is used instead of a newer available
>>>> version.
>>>>
>>>> Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
>>>> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
>>>> Link:
>>>> https://lore.kernel.org/linux-mtd/20210325102337.481172-1-s.riedmueller@phytec.de
>>>>
>>>> diff --git a/drivers/mtd/nand/raw/nand_bbt.c
>>>> b/drivers/mtd/nand/raw/nand_bbt.c
>>>> index dced32a126d9..6e25a5ce5ba9 100644
>>>> --- a/drivers/mtd/nand/raw/nand_bbt.c
>>>> +++ b/drivers/mtd/nand/raw/nand_bbt.c
>>>> @@ -525,6 +525,7 @@ static int search_bbt(struct nand_chip *this,
>>>> uint8_t
>>>> *buf,
>>>> {
>>>> u64 targetsize = nanddev_target_size(&this->base);
>>>> struct mtd_info *mtd = nand_to_mtd(this);
>>>> + struct nand_bbt_descr *bd = this->badblock_pattern;
>>>> int i, chips;
>>>> int startblock, block, dir;
>>>> int scanlen = mtd->writesize + mtd->oobsize;
>>>> @@ -560,6 +561,10 @@ static int search_bbt(struct nand_chip *this,
>>>> uint8_t
>>>> *buf,
>>>> int actblock = startblock + dir * block;
>>>> loff_t offs = (loff_t)actblock << this-
>>>>> bbt_erase_shift;
>>>>
>>>> + /* Check if block is marked bad */
>>>> + if (scan_block_fast(this, bd, offs, buf))
>>>> + continue;
>>>> +
>>>> /* Read first page */
>>>> scan_read(this, buf, offs, mtd->writesize, td);
>>>> if (!check_pattern(buf, scanlen, mtd->writesize,
>>>> td)) {
>>>>
>>>>
>>>> Thanks,
>>>> Miquèl
>>
>> Thanks,
>> Miquèl