Re: [Qemu-devel] [Qemu-arm] Warning when DTB memory nodes are noped

Re: [Qemu-devel] [Qemu-arm] Warning when DTB memory nodes are noped

[Peter Maydell]

On Thu, 13 Dec 2018 at 14:42, Jünger, Lukas
<lukas.juenger@rwth-aachen.de> wrote:
>
> Hi all,
>
> If I understand correctly, all memory nodes contained in a DTB passed
> via the -dtb option are noped in hw/arm/boot.c:556-568.
> I did not expect this to happen and only figured it out by debugging
> the kernel.
> Do you think a warning should be issued if a DTB contains memory
> regions that are noped?

No, because generally we expect that to happen: the DTB will
have a memory node for whatever the stock amount of RAM on the
target board is, but we want to delete that so we can replace
it with a memory node saying that the system has however much
RAM the user asked for on the command line.

Was the deletion of the memory node actually wrong in your case?
If so we should look at fixing the wrong behaviour, rather than
just being noisier about what we're doing...

thanks
-- PMM

Re: [Qemu-devel] [Qemu-arm] Warning when DTB memory nodes are noped

[Jünger, Lukas]

On Thu, 2018-12-13 at 14:49 +0000, Peter Maydell wrote:
> On Thu, 13 Dec 2018 at 14:42, Jünger, Lukas
> <lukas.juenger@rwth-aachen.de> wrote:
> > 
> > Hi all,
> > 
> > If I understand correctly, all memory nodes contained in a DTB
> > passed
> > via the -dtb option are noped in hw/arm/boot.c:556-568.
> > I did not expect this to happen and only figured it out by
> > debugging
> > the kernel.
> > Do you think a warning should be issued if a DTB contains memory
> > regions that are noped?
> 
> No, because generally we expect that to happen: the DTB will
> have a memory node for whatever the stock amount of RAM on the
> target board is, but we want to delete that so we can replace
> it with a memory node saying that the system has however much
> RAM the user asked for on the command line.
> 
> Was the deletion of the memory node actually wrong in your case?
> If so we should look at fixing the wrong behaviour, rather than
> just being noisier about what we're doing...
> 
> thanks
> -- PMM

I see. In my case I wanted to specify the memory using the DTB that I
passed using the -dtb option. I had two memory ranges in the dtb and
they didn't show up in the kernel later on because they were noped by
QEMU. I found it confusing that QEMU makes changes to the DTB that I
passed via -dtb. 

Thanks,
Lukas

Re: [Qemu-devel] [Qemu-arm] Warning when DTB memory nodes are noped

[Peter Maydell]

On Thu, 13 Dec 2018 at 15:00, Jünger, Lukas
<lukas.juenger@rwth-aachen.de> wrote:
>
> On Thu, 2018-12-13 at 14:49 +0000, Peter Maydell wrote:
> > Was the deletion of the memory node actually wrong in your case?
> > If so we should look at fixing the wrong behaviour, rather than
> > just being noisier about what we're doing...

> I see. In my case I wanted to specify the memory using the DTB that I
> passed using the -dtb option. I had two memory ranges in the dtb and
> they didn't show up in the kernel later on because they were noped by
> QEMU. I found it confusing that QEMU makes changes to the DTB that I
> passed via -dtb.

Yeah, we don't edit the DTB much but we do fix it up to
indicate the memory, number of CPUs, kernel command line, etc
passed on the QEMU command line.

thanks
-- PMM