[U-Boot] Booting linux zImage on vexpress-a15

[Andre Wagner]

Hi @all,

I'm trying to build a linux kernel as zImage and boot it with u-boot on 
a qemu vexpress-a15 machine. The host machine is a Ubuntu 18.04.

What I tried until now:

1. Get Linux from git, export ARCH=arm and 
CROSS_COMPILE=arm-linux-gnueabihf-

2. Make Defconfig: make vexpress_defconfig

3. Enable 'Early Printk' with make menuconfig

4. Make Kernel: make

5. Get U-Boot from git, export ARCH=arm and 
CROSS_COMPILE=arm-linux-gnueabihf-

6. Make Defconfig: make vexpress_ca15_tc2_defconfig

7. Make U-Boot: make

8. Generate empty image file and mount it: truncate -s 100M image; 
mkfs.ext4 image; mount -o loop image /mnt

9. Copy zImage and DTB to image: cp arch/arm/boot/zImage /mnt ; cp 
arch/arm/boot/dts/vexpress-v2p-ca15_a7.dtb /mnt

10. Unmount Image: umount /mnt

11. Start u-boot in qemu: qemu-system-arm -m 1024M -M vexpress-a15 -cpu 
cortex-a15 -kernel u-boot -serial stdio -sd image => U-Boot comes up and 
I can hit a key to stop automount, ok so far

12. In u-boot, checking filesystem on image: ext4ls mmc 0:0 => I can see 
my zImage and my DTB file, ok so far

13. In u-boot, loading kernel: ext4load mmc 0:0 82008000 zImage => XXXX 
bytes read is shown, ok so far

14. In u-boot, loading DTB: ext4load mmc 0:0 85000000 
vexpress-v2p-ca15_a7.dtb => YYYY bytes read, ok so far

15. In u-boot, boot: bootz 82008000 - 85000000 => 'Starting kernel ....' 
and 'Uncompressing kernel done' is shown and then nothing at all...


Cross-checks I have done right now:

- Booting kernel and DTB directly from qemu with 'qemu-system-arm -m 
1024M -M vexpress-a15 -cpu cortex-a15 -kernel arch/arm/boot/zImage  -dtb 
arch/arm/boot/dts/vexpress-v2p-ca15-tc1.dtb -serial stdio' works, normal 
boot output is shown. Also the standard console device ttyAMA0 is 
available after mounting devtmpfs.

- Same setup with vexpress-a9  (uboot with vexpress_ca9x4_defconfig, 
linux with vexpress_defconfig and DTB vexpress-v2p-ca9.dtb. The kernel 
was loaded to 62008000 and the DTB to 65000000) worked, Normal boot 
output was shown.


What I don't understand right now is:

- Am I using the corrected DTB? vexpress-v2p-ca15-tc1.dtb or 
vexpress-v2p-ca15_a7.dtb ? Which is the right one?

- What are the addresses I need to load kernel and the DTB? In the 
working vexpress-a9 sample the kernel was loaded with a offset of 
2008000h and the DTB with a offset of 5000000h to start of RAM at 
60000000h. So I decided use the same offsets with the alternate start of 
RAM address of 8000000h of vexpress-a15, i.e. kernel at 82008000 and DTB 
at 85000000. Is this assumption correct?

- 'Starting kernel...' is a last message from u-boot and 'Uncompressing 
kernel done' the first from the kernels self extractor?

- Where in RAM is the zImage decompressed by u-boot bootz? Between start 
of RAM at 80000000h and kernels loadaddr at 82008000h?

- What are the differences between loading kernel and DTB by qemu 
directly and loading kernel and DTB indirectly via u-boot?


Thank you very very much for your replies in advance.


Greetings,

André


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