Re: [PATCH 2/2] arch: arm64: configs: Enable UBI and UBIFS

[Dinh Nguyen]

On 6/26/23 22:40, Lee, Kah Jing wrote:
> > -----Original Message-----
> > From: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> > Sent: Monday, 26 June, 2023 4:39 PM
> > To: Lee, Kah Jing <kah.jing.lee@xxxxxxxxx>; Dinh Nguyen
> > <dinguyen@xxxxxxxxxx>; Rob Herring <robh+dt@xxxxxxxxxx>; Krzysztof
> > Kozlowski <krzysztof.kozlowski+dt@xxxxxxxxxx>; Conor Dooley
> > <conor+dt@xxxxxxxxxx>; Catalin Marinas <catalin.marinas@xxxxxxx>; Will
> > Deacon <will@xxxxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Subject: Re: [PATCH 2/2] arch: arm64: configs: Enable UBI and UBIFS
> >
> > On 26/06/2023 06:16, Lee, Kah Jing wrote:
> > > > -----Original Message-----
> > > > From: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> > > > Sent: Saturday, 24 June, 2023 3:30 PM
> > > > To: Lee, Kah Jing <kah.jing.lee@xxxxxxxxx>; Dinh Nguyen
> > > > <dinguyen@xxxxxxxxxx>; Rob Herring <robh+dt@xxxxxxxxxx>; Krzysztof
> > > > Kozlowski <krzysztof.kozlowski+dt@xxxxxxxxxx>; Conor Dooley
> > > > <conor+dt@xxxxxxxxxx>; Catalin Marinas <catalin.marinas@xxxxxxx>;
> > > > Will Deacon <will@xxxxxxxxxx>
> > > > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > > > Subject: Re: [PATCH 2/2] arch: arm64: configs: Enable UBI and UBIFS
> > > >
> > > > On 24/06/2023 05:42, Lee, Kah Jing wrote:
> > > > > > > > So you miss init ramdisk.
> > > > > > > Currently we are using the bootargs to mount the rootfs from QSPI
> > > > > > > NOR
> > > > > > flash:
> > > > > > > [    0.000000] Kernel command line: earlycon panic=-1 ubi.mtd=1
> > > > > > root=ubi0:rootfs rootfstype=ubifs rw rootwait
> > > > > > > Is it possible to mount the ubifs rootfs with the ubifs=m config
> > > > > > > during
> > > > boot?
> > > > > > I think yes. rootfs devices are for example modules, so filesystem
> > > > > > can be as well.
> > > > > Was going through mtd ubifs page -
> > > > > http://www.linux-mtd.infradead.org/faq/ubifs.html
> > > > > Quoted: 'In order to mount UBIFS as the root file system, you have
> > > > > to compile UBIFS into the kernel (instead of compiling it as a
> > > > > kernel
> > > > > module) and specify proper kernel boot arguments and make the kernel
> > > > mount UBIFS on boot.'
> > > >
> > > > Why? Module loaded by initramfs would also understand cmdline
> > > > arguments, right?
> > > The suggestion is to use initramfs for rootfs -> remount UBIFS as chroot?
> > > The concern is additional initrd image and steps to store in the
> > > limited NOR flash (256MB, Boot data + Uboot - ~66MB, UBIFS image -
> > > ~88MB, kernel.itb - ~10MB = 164MB).
> > > With the mounting Rootfs from UBIFS volume, we can skip the initrd
> > > step, and save some space for the user operations.
> > > Let me know if I understands that correctly.
> >
> > arm64 defconfig creates huge development config for all platforms, so why
> > would you ever use it in resource-constrained system? It would barely fit.
> > defconfig modules take 50 MB alone and you don't need most of them.
> >
> > I think you misunderstood the purpose of this defconfig and now try to apply
> > some arguments for different use cases.
> Understood the point. In this case, I would drop this defconfig patch, and
> document it for customers to enable through menuconfig.
>
> Will proceed to send the v3 for only dts changes.
> Thanks for the time.
> >

You can still have the defconfig build them as modules. Then you can 
include them in your initramfs.

Dinh