Re: [Xen-devel] [PATCH v5 p2 16/19] tools/libxl: arm: Use an higher value for the GIC phandle

[Julien Grall <julien.grall.oss@xxxxxxxxx>]

Hi Ian,

On 09/04/15 17:17, Ian Jackson wrote:
> Julien Grall writes ("[PATCH v5 p2 16/19] tools/libxl: arm: Use an higher 
> value for the GIC phandle"):
>> The partial device tree may contains phandle. The Device Tree Compiler
>> tends to allocate the phandle from 1.
> 
> I have to say I have no idea what a phandle is...

A phandle is a way to reference another node in the device tree.
Any node that can referenced defines a phandle property with a unique
unsigned 32 bit value.

>> 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.
> 
> Do we control the DT compiler ?  What if it should change its
> phandle allocation algorithm ?


We don't control the DT compiler. But the algorithm of the phandle will
unlikely change. FWIW, the compiler is very tiny, it's not GCC.

I only expect people using the partial device tree in very specific use
case. Generic use case is not even possible with the current status of
non-PCI (i.e device tree) passthrough. So people control their environment.

As I said later in patch, supporting dynamic allocation will require
some rework in the device tree creation for the guest.

So I was suggesting this solution as temporary in order to not block the
DT passthrough.

>> +/*
>> + * The device tree compiler (DTC) is allocating the phandle from 1 to
>> + * onwards. Reserve a high value for the GIC phandle.
>> + */
> 
> FYI this should read "The device tree compiler (DTC) allocates phandle
> values frrom 1 onwards".

Thanks, I will update the comment.

Regards,

-- 
Julien Grall

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