Re: AW: DT with memory bank of size 0 (WAS: Re: AW: AW: Colibri imx8qxp: Missing kernel boot module)

[Julien Grall <julien@xxxxxxx>]

Hi Daniel,

On 17/09/2020 10:47, Daniel Wagner2 wrote:
> > > > Btw 8_8000_0000 is the start address of this systems DDR Main
> > > > memory, according to the Reference Manual of the i.MX8QXP.
> > > I couldn't find this value in the DT. It is possible that U-boot is
> > > modifying the memory node before jumping to Xen (or Linux).
> > >
> > > Looking at Linux, they seem to ignore any bank with size == 0. I am
> > > starting to wonder whether your DT is (ab)using it.
> > >
> > > Do you have Linux running on baremetal on this board? If so would you
> > > mind to dump the DT from the userspace (via /proc/device-tree) this
> time?
>
> I do have linux running on baremetal on the plattform.
> Created dtb and dts with devicetree-compiler:
> dtc -I fs -O dtb -o ~/dtb-dump /proc/device-tree
> dtc -I dtb -O dts -o ~/dts-dump ~/dtb-dump
>
> uploaded both to google drive:
> https://drive.google.com/drive/folders/1jbpnz35sC0NbCyEjrkLqelBsKBztW1S6
>
> You were right, after the boot, the memory node contains the second bank
> with
> size=0.
>
> memory@80000000 {
>         device_type = "memory";
>         reg = < 0x00 0x80200000 0x00 0x7fe00000 0x08 0x80000000 0x00 0x00 >;
> };
Thank you for the testing. I am glad we finally found the reason!

> > > In any case, we may want to relax the check in Xen. Any opinions?
> > Yeah, ignoring a bank with size=0 is fine. I checked the epapr and it
> doesn't
> > specify that size=0 is invalid, so I think it is actually better to ignore
> it and
> > continue even from a spec perspective.
I have sent a patch to ignore empty bank ([1]). Would you mind to test it?

The patch is based on unstable, but it should be easy to apply it on 
older release.
Best regards,

[1] https://lore.kernel.org/xen-devel/20200918171116.29005-1-julien@xxxxxxx/

--
Julien Grall