Re: MTD: Lots of mtdblock warnings on bootup logs

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Pintu,

pintu.ping@gmail.com wrote on Wed, 12 Jul 2023 19:29:39 +0530:

> Hi,
> 
> We are getting below warning messages in dmesg logs on a NAND device
> for every raw partition.
> Kernel: 5.15 ; arm64 ; NAND + ubi + squashfs
> We have some RAW partitions and one UBI partition (with ubifs/squashfs volumes).
> 
> We are seeing large numbers of these logs on the serial console that
> impact the boot time.
> [....]
> [    9.667240][    T9] Creating 58 MTD partitions on "1c98000.nand":
> [....]
> [   39.975707][  T519] mtdblock: MTD device 'uefi_a' is NAND, please
> consider using UBI block devices instead.
> [   39.975707][  T519] mtdblock: MTD device 'uefi_b' is NAND, please
> consider using UBI block devices instead.
> [....]
> 
> This was added as part of this commit:
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/drivers/mtd/mtdblock.c?h=v5.15.120&id=f41c9418c5898c01634675150696da290fb86796
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/drivers/mtd/mtdblock.c?h=v5.15.120&id=e07403a8c6be01857ff75060b2df9a1aa8320fe5
> 
> I think this warning was decided after my last year's discussion about
> mtdblock vs ubiblock for squashfs.
> 
> But these are raw NAND partitions and not mounted by us.
> 
> What is the exact meaning of these warnings ?

mtdblock is legacy, ubiblock is better (on NAND devices).

> We have both these configs enabled:
> CONFIG_MTD_BLOCK=y
> CONFIG_MTD_UBI_BLOCK=y
> 
> Through this warning, are we telling that only one of the above config
> should be enabled ?

If you don't need both, then yes.

> And the recommendation is to use ubi_block and disable mtd_block ?

Yes.

> We are already using ubiblock for mounting squashfs volumes.
> But how to get rid of these warnings for raw NAND partitions ?
> 
> Is there a way to avoid or we are missing something which we are not aware of?
> 

In theory the warning should only appear if you open the device (IOW,
only if you use it). For this to happen, you need:
96a3295c351d ("mtdblock: warn if opened on NAND")
This commit was maybe not backported to stable kernels, you can send it
to stable@vger.kernel.org in order to ask for that. I also see that the
mtdblock_ro path was not corrected, maybe that's also a problem in your
case? Same, you can adapt the above patch and send it upstream.

Thanks,
Miquèl