Re: [qemu-system-aarch64] dtb flag for aarch64 Linux kernel

[Oleksii Kurochko]

Hello Peter,

Thanks for your reply.

Hmm. In theory that's supposed to work, but it's a bit of
an odd thing to do -- generally you just let the virt
board autogenerate the DTB and you don't need to use
the -dtb option at all. (If you do this it's important
that the options you pass to the qemu binary when you
do the dumpdtb exactly match the ones you use when you
later use the virt.dtb, but it seems like you're doing that.)

I agree that it is a bit of an odd thing to do, but I need the DTB

for the Linux kernel which is loaded by my custom

bootloader, so  I decided to dump the DTB using the dumpdtb

Qemu option and then concatenate it with the kernel.

In general, it looks like that the dumpdtb option dump incorrect

the DTB file. Because when I saved the pointer to the DTB in my

bootloader, it is in x0 register if I am right, and pass it to the
Linux kernel then all is working fine. So for some reason dtb

that is already in memory differs from that generated by

the dumpdtb option.

Thanks.

Best regards,

 Oleksii

сб, 12 окт. 2019 г. в 22:20, Peter Maydell <address@hidden>:

On Sat, 12 Oct 2019 at 13:30, Oleksii Kurochko
<address@hidden> wrote:
> First I successfully booted it without dtb flag in the next way:
> qemu-system-aarch64 -M virt -cpu cortex-a57 -nographic -m 2048 -kernel kernel/arch/arm64/boot/Image -append "console=ttyAMA0"

Yes, this is the expected way to use the 'virt' board.

> After that I decided to dump dtb that is generated inside Qemu:
> qemu-system-aarch64 -M virt,dumpdtb=virt.dtb -cpu cortex-a57 -nographic -m 2048 -kernel kernel/arch/arm64/boot/Image -append "console=ttyAMA0"
>
> Finally I tried to boot it with dumped dtb:
> qemu-system-aarch64 -M virt -cpu cortex-a57 -nographic -m 2048 -kernel kernel/arch/arm64/boot/Image -append "console=ttyAMA0
> " -dtb virt.dtb
> But I did not see any messages.

Hmm. In theory that's supposed to work, but it's a bit of
an odd thing to do -- generally you just let the virt
board autogenerate the DTB and you don't need to use
the -dtb option at all. (If you do this it's important
that the options you pass to the qemu binary when you
do the dumpdtb exactly match the ones you use when you
later use the virt.dtb, but it seems like you're doing that.)

thanks
-- PMM