Re: [Xen-devel] [PATCH v3 22/24] tools/libxl: arm: Use an higher value for the GIC phandle

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 29 Jan 2015, Julien Grall wrote:
> On 29/01/15 12:28, Stefano Stabellini wrote:
> > On Thu, 29 Jan 2015, Julien Grall wrote:
> >> On 29/01/15 11:07, Stefano Stabellini wrote:
> >>> On Tue, 13 Jan 2015, Julien Grall wrote:
> >>>> The partial device tree may contains phandle. The Device Tree Compiler
> >>>> tends to allocate the phandle from 1.
> >>>>
> >>>> Reserve the ID 65000 for the GIC phandle. I think we can safely assume
> >>>> that the partial device tree will never contain a such ID.
> >>>>
> >>>> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> >>>> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> >>>> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> >>>>
> >>>
> >>> Shouldn't we at least check that the partial device tree doesn't contain
> >>> a conflicting phandle?
> >>
> >> I don't think so. This will unlikely happen, and if it happens the guest
> >> will crash with an obvious error.
> > 
> > It is good that the error is obvious.
> > 
> > But how expensive is to check for it?
> 
> I would have to check the validity of the properties (name + value
> size). At least the properties "linux,phandle" and "phandle" should be
> checked.
> 
> Though I could do in copy_properties but I find it hackish.
> 
> > Think about the poor user that ends up in this situation: the fact that
> > is unlikely only makes it harder for a user to figure out what to do to
> > fix it.
> 
> The poor use will have to write his device tree by hand to hit this
> error ;).
> 
> So using the right phandle is not a huge drawback.

Fair enough.  Please document this limitation in the docs and/or manuals.

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