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

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

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

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.


Julien Grall

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