[PATCH v6 09/25] arm: xenguest_arm64: Add a fake devicetree file

Simon Glass sjg at chromium.org
Fri Dec 3 17:23:01 CET 2021

Hi Oleksandr,

On Thu, 2 Dec 2021 at 22:41, Oleksandr Andrushchenko
<Oleksandr_Andrushchenko at epam.com> wrote:
> Hi, Simon!
> On 02.12.21 19:57, Simon Glass wrote:
> > Hi Oleksandr,
> >
> > On Thu, 2 Dec 2021 at 10:40, Oleksandr Andrushchenko
> > <Oleksandr_Andrushchenko at epam.com> wrote:
> >> Hi, Simon!
> >>
> >> Sorry for being late to the party
> >>
> >> On 02.12.21 17:59, Simon Glass wrote:
> >>> Add an empty file to prevent build errors when building with
> >>> CONFIG_OF_SEPARATE enabled.
> >>>
> >>> The build instructions in U-Boot do not provide enough detail to build a
> >>> useful devicetree, unfortunately.
> >> Xen guest doesn't use any built-in device trees as the guest's device tree is provided
> >> by the Xen hypervisor itself and is generated at the virtual machine creation time: it is
> >> populated with memory size, number of CPUs etc. based on [1].
> >> So, even if we provide some device tree here it must not be used by U-boot at
> >> the end of the day. Thus, it might be a reasonable solution to provide an empty device
> >> tree as you do, but put a comment that it is not used.
> > OK we can go with an empty one if we have to, but where are the
> > instructions to create the DT that is used?
> You don't need to create the device tree yourself, but instead it is
> provided by Xen and generated at run-time while creating a
> virtual machine. So, it is up to Xen to provide one.
> There are cases [1] when you may want providing a so called
> partial device tree to better tune what a virtual machine gets.
> But again, it is used by Xen toolstack outside of the virtual machine
> and serves as a sort of overlay to the generated device tree.
> So, we can provide some device tree to be embedded in U-boot,
> but it will have no practical meaning and will make more harm than good
> >
> > I'm not even sure how to run U-Boot with Xen? The in-tree instructions
> > don't help...
> This is just a virtual machine from Xen POV, so U-boot is nothing
> different here from Linux kernel or anything else.
> Thus no specific instructions are needed nor provided

I'd like to try it out. How??


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