[PATCH V8] kbuild: create a rule to run the pre-processor on *.dts files

[Stephen Warren]

On 02/08/2013 07:45 AM, Grant Likely wrote:
> On Tue,  5 Feb 2013 12:06:28 -0700, Stephen Warren <swarren at wwwdotorg.org> wrote:
>> From: Stephen Warren <swarren at nvidia.com>
>>
>> Create cmd_dtc_cpp to run the C pre-processor on *.dts file before
>> passing them to dtc for final compilation. This allows the use of #define
>> and #include within the .dts file.
>>
>> Acked-by: Simon Glass <sjg at chromium.org>
>> Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj at jcrosoft.com>
>> Acked-by: Michal Marek <mmarek at suse.cz>
>> Acked-by: Srinivas Kandagatla <srinivas.kandagatla at st.com>
>> Signed-off-by: Stephen Warren <swarren at nvidia.com>
> 
> I've applied this and was going to push it out, but I've just thought of
> a problem that could be a show stopper. Once a dtsp file includes a C
> header, the contents of that header become part of the Device Tree ABI.
> If someone changes that file (ie. to renumber a series of #defines) then
> that will break the binding. We need a way to protect against that.
> Someone changing a .h file may make the assumption that it is only
> kernel internal and won't realize that it has external implications.
> 
> I'm thinking that any dts includes need to be treated in the same way as
> userspace headers. We could put them into include/uapi and piggy back on
> the protection already afforded by that directory, or come up with
> something new. Any thoughts?

Yes, that's true.

What protection is provided by include/uapi - something programmatic or
simply stricter review?

I wondered if we shouldn't put the headers into the .dts directory, then
update the kernel to include them too. That would also make it obvious
they were part of the DT ABI.