Re: UBIFS on write-protected NAND

[Richard Weinberger <richard.weinberger@gmail.com>]

On Sun, Jun 2, 2019 at 4:08 PM Leon Pollak <leon.pollak@gmail.com> wrote:
>
> I am sorry to disturb the list with the problem most probably already
> solved ion later versions...
>
> I am running Linux 2.6.32 from TI and my root FS is on NAND UBIFS.
> Linux boots with command line:
> root=ubi0:ubi_rootfs ro noinitrd ubi.mtd=4,2048 rootfstype=ubifs
> Please, note the "ro" in the command line.
> Also the HW write-protect line is always set to "protected" state.
> UBIFS stays most of the time in write protected HW state (system
> requirement) and RO mounted, except the very rare cases when some
> update is required.
>
> For this update purpose:
> - HW write-protect is removed in SW;
> - root FS is remounted to RW (mount -o remount,rw /);
> - the change is performed;
> - sync, sleep 3;
> - mount -o,remount,ro / ;
> - sleep 2, return HW write-protection;
> - reboot.
>
> For some unknown reason (may be you know?), sometimes something still
> remains in journal and on the next boot we receive a bundle of error
> messages with error codes -5 and -30. This happens despite the RO

More details please. Can you share a full back trace?

But in general a re-mount to ro does not guarantee a clean journal.
All it does is making sure that no new files can be opened in write-mode,
it is a VFS thing. UBIFS tries to be nice as possible and disables further
writes. Maybe your kernel has a bug, it is very old. Dunno...

> state of the FS and effectively blocks all the system:
> - after these errors detection, UBIFS switches to read-only state,
> blocking any possible corrections/repairs.
> - we can't remove HW protection to allow it to finish desired work as
> it happens in the Linux boot, when initd is just starting.
>
> Now, I suppose that this issue (that everything is RO and shouldn't be
> tried to recover) is treated already in the new versions. My problem
> is that I can't move to newer Linux because of TI HW.
>
> So, my questions are:
> 1. Where in the code of UBI (UBIFS?) can I insert the HW write-protect
> removal in order to allow the UBI/UBIFS to do its desired work?
> 2. When can I put write-protection back?

Using a write protected NAND is not recommend.
You basically remove the wear-leveling feature from UBI.
Blocks can gain bit-flips also in a read-only environment, consider
read disturb or other influences such as temperature changes.

-- 
Thanks,
//richard

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