[U-Boot] [nand] [ubi] Discrepancy Between U-Boot and Linux NAND PEBs

[Ken Sloat]

> -----Original Message-----
> From: Heiko Schocher <hs at denx.de>
> Sent: Monday, June 24, 2019 3:41 AM
> To: Ken Sloat <KSloat at aampglobal.com>
> Cc: oss at buserror.net; tudor.ambarus at microchip.com;
> kmpark at infradead.org; hs at denx.de; u-boot at lists.denx.de; linux-
> mtd at lists.infradead.org
> Subject: Re: [U-Boot] [nand] [ubi] Discrepancy Between U-Boot and Linux
> NAND PEBs
> 
> [This is an EXTERNAL EMAIL]
> ________________________________
> 
> Hello Ken,
> 
> Am 20.06.2019 um 14:55 schrieb Ken Sloat:
> > Hello All,
> >
> > I have been working on a system using a NAND flash along with U-Boot
> 2018.07 and Linux Kernel 4.14. This is an Atmel based system FYI so it uses the
> Atmel NAND driver. I create a UBI image with 3 separate volumes - 2 of these
> are a specified fixed size and the third is specified as the minimum needed to
> hold the current files with the auto resize flag set. As a note, before the first
> run auto resize operation, there is over 200 MiB of unused space in the
> NAND - meaning there should be plenty of free space available for UBI to
> leave overhead when auto-resizing for bad block handling. Another point of
> note, is that I use UBI within U-Boot as well in order to read the kernel image
> and dtb out of the UBIFS.
> >
> > I have noticed warnings in Linux when attaching UBI regarding not having
> enough reserved PEBs for bad block handling (it's short by 2). Upon further
> investigation into the issue, it appears as though there is a discrepancy
> between what U-Boot and Linux see in terms of the number of bad blocks:
> >
> > U-Boot:
> > ubi0: good PEBs: 4093, bad PEBs: 3, corrupted PEBs: 0
> > ubi0: user volume: 3, internal volumes: 1, max. volumes count: 128
> >
> > Linux:
> > ubi0 warning: ubi_eba_init: cannot reserve enough PEBs for bad PEB
> handling, reserved 71, need 73
> > ......
> > ubi0: good PEBs: 4089, bad PEBs: 7, corrupted PEBs: 0
> > ubi0: user volume: 3, internal volumes: 1, max. volumes count: 128
> >
> > After production flashing of a UBI image to NAND (with a "dumb" non UBI
> aware flasher), U-Boot will be the program to mount UBI. What this means is
> that it will complete the one time re-size operation. I used a Linux ramdisk
> image to flash from Linux and mount UBI in Linux for the first time to allow it
> to complete the auto-resize operation instead and compared:
> >
> > U-Boot:
> > ubi0: attaching mtd1
> > ubi0: scanning is finished
> > ubi0: volume 1 ("rootfs") re-sized from 1501 to 3385 LEBs
> > ubi0: attached mtd1 (name "mtd=0", size 512 MiB)
> > ubi0: PEB size: 131072 bytes (128 KiB), LEB size: 126976 bytes
> > ubi0: min./max. I/O unit sizes: 2048/2048, sub-page size 2048
> > ubi0: VID header offset: 2048 (aligned 2048), data offset: 4096
> > ubi0: good PEBs: 4093, bad PEBs: 3, corrupted PEBs: 0
> >
> > Linux:
> > ubi0: attaching mtd6
> > ubi0: scanning is finished
> > ubi0: volume 1 ("rootfs") re-sized from 1501 to 3383 LEBs
> > ubi0: attached mtd6 (name "atmel_nand", size 512 MiB)
> > ubi0: PEB size: 131072 bytes (128 KiB), LEB size: 126976 bytes
> > ubi0: min./max. I/O unit sizes: 2048/2048, sub-page size 2048
> > ubi0: VID header offset: 2048 (aligned 2048), data offset: 4096
> > ubi0: good PEBs: 4089, bad PEBs: 7, corrupted PEBs: 0
> >
> > As you can see, U-Boot resizes the image to 3385 blocks while Linux only
> 3383 - hence the 2 blocks that Linux would complain about had U-Boot
> resized the volume.
> >
> > I am not sure exactly what is causing this discrepancy as I just figured this
> out - but thought I would reach out and discuss it here. Obviously there are
> ways around this issue (program and mount UBI from Linux initially, don't use
> autoresize and specify all volume sizes, etc) but was wondering if there is
> some underlying problem. I noticed an older mailing discussion from several
> years ago where someone reported a similar issue regarding number of bad
> PEBs and seems the issue was chalked up to a potential driver problem on
> one side:
> > https://lists.denx.de/pipermail/u-boot/2015-June/216482.html
> >
> > Any insight would be helpful.
> 
> We use in U-Boot the code from linux 4.2 (commit
> 64291f7db5bd8150a74ad2036f1037e6a0428df2)
> (Yes, very old in the meantime)
> 
> So may there is a problem with this old code base in U-Boot?
> 
> Volunteers for rebasing the U-Boot ubi/ubifs code with a newer
> linux version are welcome.
> 
> But reading your Email again, may you should first investigate, why U-Boot
> and Linux see different good PEBs.
> 
> Also your kernel drops the warning:
> 
> ubi0 warning: ubi_eba_init: cannot reserve enough PEBs for bad PEB
> handling, reserved 71, need 73
> 
> You should look here deeper into it.
> 
> bye,
> Heiko
> --
> DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
> Phone: +49-8142-66989-52   Fax: +49-8142-66989-80   Email: hs at denx.de

Thanks for the info Heiko,

I will see what I can find

Thanks,
Ken Sloat