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

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 23/02/2015 14:36, Ian Campbell wrote:
> On Thu, 2015-01-29 at 13:48 +0000, 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.
> Can't you just track the largest phandle ever seen during
> copy_properties and then use N+1 for the GIC?
Now the we decided to trust the input device tree, it would be easier to 
write the code.
I will give a look.

> > > 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 ;).
> Or use a new version of dtc which does things differently for some
> reason.
And you would not be able to get a phandle for the GIC if largest 
phandle is too high.
So the guest won't work correctly.

Regards,

--
Julien Grall

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