How u-boot can chain "grub" and booting a mainline kernel on my ARM Chromebook

[Peter Robinson]

On Sat, Jul 1, 2023 at 1:25 PM Mario Marietto <marietto2008 at gmail.com> wrote:
>
> Hello.
>
> I would like to enable KVM virtualization on my old ARM Chromebook
> laptop,based on the Exynos5250 arm 32 bit cpu aka snow,model xe303c12.

Upstream Linux kernel dropped support for running virt on 32 bit hosts
(you can still run a 32 bit guest on a 64 bit host) in the upstream
linux kernel with the 5.7 release (May 31st, 2020) so you'll probably
have to run a 5.4.x LTS kernel rather than 5.18.x (not sure why you
chose that one) at the very least.

> The first thing I did has been to dd the image below directly on the sd
> card :
>
> https://github.com/hexdump0815/imagebuilder/releases/download/220619-01/chromebook_snow-armv7l-jammy.img.gz
>
> and it worked like a charm,but kvm was disabled. So,I have started to look
> for a good documentation to understand how to enable kvm and I found this :
>
> http://www.virtualopensystems.com/en/solutions/guides/kvm-on-chromebook/
>
> I've followed all the instructions and it worked,but only with Ubuntu 13.04
> and 14.04. More upgraded ubuntu versions give a lot of problems and they
> don't work.
>
> So,I've thought about a fresh idea. What about to install the virtual open
> systems "non-verified u-boot" on the first partition like explained in the
> tutorial,and,instead of starting another u-boot after the original,can I
> chain grub with the kernel installed for example by the ubuntu jammy iso
> image created by "hexdump0815" ? To be honest I'm not sure if hexdump0815
> used grub,but I will explain this later.
>
> Anyway,I've got the idea by reading here :
>
> https://unix.stackexchange.com/questions/599141/how-to-install-grub-bootloader-as-second-stage-bootloader
> So,now,I'm going to explain what's the content of the partitions on my
> Frankenstein sd card.
>
> 1) /dev/sdh1 = unknown = 16 MB. I've created this partition by doing :
>
> $ sudo dd if=nv_uboot-snow.kpart of=/dev/sdh1
>
> Where I've got the file nv_uboot-snow.kpart ? From here :
>
> http://www.virtualopensystems.com/downloads/guides/kvm_on_chromebook/nv_u-boot-snow.kpart
>
> 2) /dev/sdh2 = unknown = 16 MB. This partition has been created by
> executing the following
>
> script :
>
> $ sudo ./scripts/sdcard.sh /dev/sdh
>
> 3) /dev/sdh3 = ext2 BOOT.
>
> Inside the partition /dev/sdh3 I have copied the following files and
> folders (taken
> from the hexdump0815 "chromebook_snow-armv7l-jammy.img.gz" file :
>
> a) dtb-5.18.1-stb-cbe+ = directory
> b) extlinux = directory
> c) extra = directory
>
> d) config.5.18.1-stb-cbe+ : file
> e) initrd.img-5.18.1-stb-cbe+ : file
> f) System.map-5.18.1-stb-cbe+ : file
> g) vmlinux.kpart-5.18.1-stb-cbe+ : file
> h) zImage-5.18.1-stb.cbe+ : file
>
> Inside the directory "dtb-5.18.1-stb-cbe+" there are the following files :
>
> a) exynos5250-snow.dtb
> b) exynos5250-snow-rev5.dtb
> c) exynos5250-spring.dtb
>
> Inside the directory "extlinux",there is the following file :
>
> a) extlinux.conf : that has the following content :
>
> TIMEOUT 30
>
> DEFAULT linux-snow-rev4
>
> MENU TITLE snow chromebook boot options
>
> # rev4 snow chromebook
> LABEL linux-snow-rev4
>       MENU LABEL linux rev4 snow
>       LINUX ../zImage-5.18.1-stb-cbe+
>       INITRD ../initrd.img-5.18.1-stb-cbe+
>       FDT ../dtb-5.18.1-stb-cbe+/exynos5250-snow.dtb
>       APPEND console=tty1 root=LABEL=rootpart ro rootwait net.ifnames=0
> ipv6.disable=1 fsck.repair=yes noresume
>
> # rev5 snow chromebook
> LABEL linux-snow-rev5
>       MENU LABEL linux rev5 snow
>       LINUX ../zImage-5.18.1-stb-cbe+
>       INITRD ../initrd.img-5.18.1-stb-cbe+
>       FDT ../dtb-5.18.1-stb-cbe+/exynos5250-snow-rev5.dtb
>       APPEND console=tty1 root=LABEL=rootpart ro rootwait net.ifnames=0
> ipv6.disable=1 fsck.repair=yes noresume
>
> # spring chromebook - untested
> LABEL linux-spring
>       MENU LABEL linux spring
>       LINUX ../zImage-5.18.1-stb-cbe+
>       INITRD ../initrd.img-5.18.1-stb-cbe+
>       # rev4 snow chromebook
>       FDT ../dtb-5.18.1-stb-cbe+/exynos5250-spring.dtb
>       APPEND console=tty1 root=LABEL=rootpart ro rootwait net.ifnames=0
> ipv6.disable=1 fsck.repair=yes noresume
>
> Inside the extra directory there are the following files :
>
> a) kernel-chromebook_snow-legacy.tar.gz
> b) uboot.kpart.cbe-snow
> c) uboot.kpart.cbe-snow-alternative
> d) uboot.kpart.cbe-spring
>
> 4) /dev/sdh4 : inside here I have copied all the files of the jammy
> userland prepared by hexdump0818.
>
> That's all. What I want to do is if and how can I chainload the
> "non-verified u-boot"
> that is installed on the partition /dev/sdh1 with grub or whatever
> mechanism it is able to boot the hexdump0815 jammy iso image.
>
> As I repeat,the "non-verified u-boot" is produced by the script called
> "build.sh",that's stored inside the u-boot/scripts directory. And if what I
> want to do is impossible,can you explain to me how I can enable kvm on my
> chromebook arm,using the most recent kernel possible ? I already know that
> the support for kvm on arm 32 has been dropped on kernel 5.7,but for me to
> use a lower kernel than 5.7 is ok. I've been working on this project for a
> lot of months. I would like to see some progress. Thanks.
>
> --
> Mario.