Re: [PATCH v5 19/19] libxl: build a device tree for ARM guests

[Julien Grall <julien.grall@linaro.org>]

On 11/14/2013 12:17 PM, Stefano Stabellini wrote:
> On Thu, 14 Nov 2013, Ian Jackson wrote:
>> Ian Campbell writes ("[PATCH v5 19/19] libxl: build a device tree for ARM guests"):
>>> Uses xc_dom_devicetree_mem which was just added. The call to this needs to be
>>> carefully sequenced to be after xc_dom_parse_image (so we can tell which kind
>>> of guest we are building, although we don't use this yet) and before
>>> xc_dom_mem_init which tries to decide where to place the FDT in guest RAM.
>>>
>>> Removes libxl_noarch which would only have been used by IA64 after this
>>> change. Remove IA64 as part of this patch.
>>>
>>> There is no attempt to expose this as a configuration setting for the user.
>>>
>>> Includes a debug hook to dump the dtb to a file for inspection.
>>
>> Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
>>
>>> TODO:
>>> - v7 CPU compat is hardcoded to cortex-a15 -- may need to define something more
>>>    generic via mach-virt dt bindngs?
>>
>> I don't have an opinion on this.  I hope someone else does :-).
>
> Wouldn't it be better to use the same cpu compatibility string of the
> platform? After all it's the physical cpu that we are time slicing for
> the guest: if any quirks are present, it is likely that they are going
> to affect the guest too.
>

/proc doesn't always expose the device tree. It depends on 
CONFIG_PROC_DEVICETREE:
	- if it's enabled, you will still need to browse all the directory to 
find where are the cpus node. But you will need to assume all CPUs are 
homogeneous.
         - if it's not enabled, you will need to create a fake one based 
on, for instance, /proc/cpuinfo.

In any case, Linux doesn't seem to care about the cpu compatible string 
for now.

-- 
Julien Grall