dtc: import latest upstream dtc

[Mitch Bradley]

On 10/10/2012 8:45 AM, Stephen Warren wrote:
> On 10/10/2012 12:23 PM, Mitch Bradley wrote:
>> On 10/10/2012 7:09 AM, Rob Herring wrote:
>>> On 10/09/2012 04:16 PM, Stephen Warren wrote:
>>>> On 10/01/2012 12:39 PM, Jon Loeliger wrote:
>>>>>>
>>>>>> What more do you think needs discussion re: dtc+cpp?
>>>>>
>>>>> How not to abuse the ever-loving shit out of it? :-)
>>>>
>>>> Perhaps we can just handle this through the regular patch review
>>>> process; I think it may be difficult to define and agree upon exactly
>>>> what "abuse" means ahead of time, but it's probably going to be easy
>>>> enough to recognize it when one sees it?
>>>
>>> Rather than repeating things over and over in reviews, we should
>>> document at least rules we can easily agree on and then add to it when
>>> people get "creative." Also, I can't keep up with every single binding
>>> review as is, and this could just add another level of complexity to the
>>> review. A few off the top of my head and from the thread discussion:
>>>
>>> - Headers must be self contained with no outside (i.e. libc, kernel,
>>> etc.) header dependencies.
>>> - No kernel kconfig option usage
>>> - No gcc built-in define usage
>>> - No unused items (i.e. externs, structs, etc.)
>>> - No macro concatenation
>>> - No macros for strings or property names
>>
>> Instead of making a bunch of rules about how you can only use a small
>> subset of cpp, why not just add a "define name value" command to DTC?
> 
> I implemented a patch to do exactly that, and it was rejected because it
> only solved part of the problem (named constants) and not the reset (a
> completely generic macro language/... within dtc). The argument was that
> defining just the named constant syntax on its own without knowing what
> the unspecified future macro language will look like might result in the
> named constant syntax not fitting into it.
> 
> That all said, I now think that using cpp is actually a much better
> solution that adding yet more dtc-specific syntax. The *huge* benefit
> here is that it allows you to share .h files between *.dts and C code,
> so you don't have to write out the same set of #defines once in dtc
> syntax and once in cpp syntax.

... and it imposes an equally *huge* restriction that you have to
restrict the .h file to avoid avoid C constructs.  That can be done, but
I've personally experienced a lot of headaches when trying to share .h
files between different languages.

>