Re: [Xen-devel] [PATCH 04/12] arm: parse modules from DT during early boot.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 3 Dec 2012, Ian Campbell wrote:
> > > diff --git a/docs/misc/arm/device-tree/booting.txt 
> > > b/docs/misc/arm/device-tree/booting.txt
> > > new file mode 100644
> > > index 0000000..2609450
> > > --- /dev/null
> > > +++ b/docs/misc/arm/device-tree/booting.txt
> > > @@ -0,0 +1,27 @@
> > > +Xen is passed the dom0 kernel and initrd via a reference in the /chosen
> > > +node of the device tree.
> > > +
> > > +Each node has the form /chosen/module@<N> and contains the following
> > > +properties:
> > 
> > Wouldn't it be better to move all the modules under /chosen/modules or
> > /chosen/multiboot?
> 
> Why, what's the benefit?
> 
> I'm happy to do whatever is more normal in DT. Is that this:
>       /foo/bar@1
>       /foo/bar@2
> or
>       /foo/bar/bar@1
>       /foo/bar/bar@2
> 
> The second (which I think is what you are suggesting) seems pretty
> redundant.

To be precise I am suggesting:

/foo/bars/bar@0
/foo/bars/bar@1

I think it is just clearer, especially if more stuff end up inside
/chosen. Also see how the cpus node is defined, for example.


> > > +- compatible
> > > +
> > > + Must be "xen,multiboot-module"
> > > +
> > > +- start
> > > +
> > > + Physical address of the start of this module
> > > +
> > > +- end
> > > +
> > > + Physical address of the end of this module
> > 
> > start and end could be encoded as one reg
> 
> Done.
> 
> > 
> > 
> > > +- bootargs (optional)
> > > +
> > > + Command line associated with this module
> > > +
> > > +The following modules are understood
> > > +
> > > +- 1 -- the domain 0 kernel
> > > +- 2 -- the domain 0 ramdisk
> > 
> > It would be nice if we could express this via the compatible property
> > instead.
> > So the linux kernel could be compatible "linux,kernel" and the initrd
> > "linux,initrd", in addition to (or instead of) "xen,multiboot-module".
> > Given that they go from the most specific to the less specific, it would
> > become:
> > 
> > compatible = "linux,kernel", "xen,multiboot-module";
> 
> This bakes the word "linux" into the interface and would require a new
> compatible tag and code changes in Xen for each new dom0 kernel type,
> which I think we want to avoid. (maybe the code changes are unavoidable
> in practice, but in principal...)
> 
> "xen,dom0-kernel", "xen,multiboot-module"
> 
> Might be an option?
> 
> I'm going to repost what I have without changing this bit yet.

"xem,dom0-kernel" is OK.
However what about the initrd? Does Xen need to know that the second
module is the kernel's initrd or is it just another opaque module from
Xen's point of view?
If Xen needs to know that it is an initrd I think we need to introduce
another compatible string. Maybe the following:

"xen,dom0-initrd"

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