Date: Wed, 10 Oct 2012 11:09:53 -0500
From: Scott Wood <scottwood@freescale.com>
Subject: Re: dtc: import latest upstream dtc
To: Stephen Warren <swarren@wwwdotorg.org>
CC: Mitch Bradley <wmb@firmworks.com>, Michal Marek <mmarek@suse.cz>,
        Stephen Warren <swarren@nvidia.com>,
        <devicetree-discuss@lists.ozlabs.org>, <linux-kernel@vger.kernel.org>
References: <1349827466.26044.16@snotra> <50759105.2000406@wwwdotorg.org>
In-Reply-To: <50759105.2000406@wwwdotorg.org> (from swarren@wwwdotorg.org on
	Wed Oct 10 10:15:17 2012)
Message-ID: <1349885393.21493.2@snotra>
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On 10/10/2012 10:15:17 AM, Stephen Warren wrote:
> On 10/09/2012 06:04 PM, Scott Wood wrote:
> > On 10/09/2012 06:20:53 PM, Mitch Bradley wrote:
> >> On 10/9/2012 11:16 AM, 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?
> >>
> >>
> >> One of the ways it could get out of hand would be via "include
> >> dependency hell".  People will be tempted to reuse existing .h  
> files
> >> containing pin definitions, which, if history is a guide, will end  
> up
> >> depending on all sorts of other .h files.
> >>
> >> Another problem I often face with symbolic names is the difficulty  
> of
> >> figuring out what the numerical values really are (for debugging),
> >> especially when .h files are in different subtrees from the files  
> that
> >> use the definitions, and when they use multiple macro levels and  
> fancy
> >> features like concatenation.  Sometimes I think it's clearer just  
> to
> >> write the number and use a comment to say what it is.
> >
> > Both comments apply just as well to ordinary C code, and I don't  
> think
> > anyone would seriously suggest just using comments instead for C  
> code.
> >
> > Is there a way to ask CPP to evaluate a macro in the context of the
> > input file, rather than produce normal output?  If not, I guess you
> > could make a tool that creates a wrapper file that includes the main
> > file and then evaluates the symbol you want.
> 
> I'm not sure what "evaluate a macro in the context of the input file"
> means. Macros are obviously already evaluated based on the current set
> of macros defined by the file that's been processed or those it
> included. Do you mean only allowing the use of macros in the current
> file and not included files? What exactly would the wrapper you
> mentioned do?

I just meant a way for a developer to quickly ask the preprocessor what  
a particular macro expands to, rather than try to figure it out  
manually.  I was not suggesting any change to normal operation.

-Scott
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